Lithium secondary battery

Abstract

The purpose of the present invention is to provide a means, in a lithium deposition-type lithium secondary battery, for realizing rate characteristics that support quick charging. An embodiment of the present invention relates to a lithium secondary battery that is provided with an electric power generation element comprising: a positive electrode that is constituted by a positive electrode active material layer, which contains a positive electrode active material capable of storing and releasing lithium ions, being disposed on the surface of a positive electrode current collector; a negative electrode that has a negative electrode current collector on which lithium metal is deposited during charging; and a solid electrolyte layer that is interposed between the positive electrode and the negative electrode, and that contains a solid electrolyte. This lithium secondary battery is characterized in that, in at least a portion of a region of a main surface of the negative electrode current collector facing the solid electrolyte layer, where the positive electrode active material layer faces the negative electrode current collector, there is disposed a carbon particle layer including carbon particles that have an intensity ratio R(IG / ID) of 7 or more of a G-band peak intensity (IG) and a D-band peak intensity (ID) measured by Raman spectroscopy.

Description

Lithium secondary battery

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

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. In the automotive industry, there is growing hope for a reduction in carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and non-aqueous electrolyte secondary batteries, such as secondary batteries for driving motors, which hold the key to their practical application, have been actively developed.

[0003] Secondary batteries for driving motors are required to have extremely high output characteristics and high energy compared to consumer lithium-ion secondary batteries used in mobile phones, laptops, etc. Therefore, lithium-ion secondary batteries, which have the highest theoretical energy of all practical batteries, have attracted attention and are currently being rapidly developed.

[0004] Currently widely used lithium-ion secondary batteries use flammable organic electrolytes, and these liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, overcharging, and other issues than other batteries.

[0005] Therefore, in recent years, research and development on all-solid-state lithium secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively conducted. Solid electrolytes are materials composed primarily of ionic conductors that can conduct ions in a solid state. Therefore, all-solid-state lithium secondary batteries do not, in principle, encounter the various problems associated with flammable organic electrolytes that occur in conventional liquid-based lithium-ion secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the output density and energy density of the battery.

[0006] Conventionally, one type of all-solid-state lithium secondary battery known is a so-called lithium deposition type, in which lithium metal is deposited on a negative electrode current collector during charging. During charging of such a lithium deposition type all-solid-state lithium secondary battery, lithium metal is deposited between the solid electrolyte layer and the negative electrode current collector.

[0007] Conventionally, as a technique for improving charge-discharge characteristics such as discharge capacity density and cycle characteristics of all-solid-state lithium secondary batteries, Japanese Patent Application Laid-Open No. 2014-93156 discloses a sheet-like electrode in which an electrode active material layer containing a particulate electrode active material, a conductive resin layer, and a current collector layer are laminated, and an example of the same document discloses that the sheet-like electrode is used as the positive electrode of a lithium deposition-type all-solid-state lithium secondary battery.

[0008] The present inventors have also investigated the techniques described in the above-mentioned documents while developing technologies for improving the rapid charging characteristics of lithium secondary batteries. However, the inventors' investigations have revealed that even when the techniques described in the above-mentioned documents are used, sufficient rapid charging characteristics may not be achieved in some cases.

[0009] Therefore, an object of the present invention is to provide a means for enabling a lithium deposition type lithium secondary battery to exhibit rate characteristics that are compatible with rapid charging.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, it has been discovered that in a lithium deposition type lithium secondary battery, a conductive layer is disposed on the main surface of a negative electrode current collector that faces a solid electrolyte layer, and that the G-band peak intensity (I Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ The present inventors have found that the above problems can be solved by incorporating carbon particles having a specific value or more in the conductive layer, and have completed the present invention.

[0011] That is, one aspect of the present invention relates to a lithium secondary battery including a power generating element including a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions and disposed on the surface of a positive electrode current collector, a negative electrode including a negative electrode current collector and in which lithium metal is deposited on the negative electrode current collector during charging, and a solid electrolyte layer containing a solid electrolyte interposed between the positive electrode and the negative electrode. In the lithium secondary battery, a G-band peak intensity (I) measured by Raman scattering spectroscopy is present in at least a part of a region of the main surface of the negative electrode current collector facing the solid electrolyte layer, where the positive electrode active material layer faces the negative electrode current collector. Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ The carbon particle layer is characterized in that it contains carbon particles having a saturation coefficient of 7 or more.

[0012] Fig. 1 is a perspective view showing the appearance of a flat stacked type all-solid-state lithium secondary battery according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 shown in Fig. 1. Fig. 2 shows a cross-sectional view of the stacked secondary battery during charging. Fig. 3 is an enlarged cross-sectional view of a single cell layer of the stacked secondary battery according to one embodiment of the present invention.

[0013] One aspect of the present invention provides a power generating element including a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions, disposed on the surface of a positive electrode current collector; a negative electrode having a negative electrode current collector and in which lithium metal is deposited on the negative electrode current collector during charging; and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein a G-band peak intensity (I) measured by Raman scattering spectroscopy is detected in at least a part of a region of the main surface of the negative electrode current collector facing the solid electrolyte layer, where the positive electrode active material layer faces the negative electrode current collector. Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ The present invention provides a lithium secondary battery having a carbon particle layer including carbon particles having a ρ of 7 or more. According to the present invention, a lithium deposition type lithium secondary battery can exhibit rate characteristics that can accommodate rapid charging.

[0014] The present embodiment will be described below with reference to the drawings, but the technical scope of the present invention should be determined based on the description of the claims and is not limited to the following embodiment. Note that the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0015] Fig. 1 is a perspective view showing the appearance of a flat stacked-type all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 shown in Fig. 1. Fig. 2 shows a cross-sectional view of the stacked-type secondary battery during charging.

[0016] As shown in Fig. 1, the stacked secondary battery 10a has a flat rectangular shape, with a negative current collector 25 and a positive current collector 27 extending from both sides for extracting power. The power generating element 21 is wrapped in the battery exterior material (laminate film 29) of the stacked secondary battery 10a, and the periphery is heat-sealed, sealing the power generating element 21 with the negative current collector 25 and the positive current collector 27 extending to the outside. Note that the current collectors (25, 27) shown in Fig. 1 may be configured so that the negative current collector 25 and the positive current collector 27 extend from the same side, or the negative current collector 25 and the positive current collector 27 may each be divided into multiple plates and extended from each side.

[0017] As shown in FIG. 2 , during charging, the power generating element 21 of the stacked secondary battery 10 a of this embodiment has a configuration in which a negative electrode in which a negative electrode active material layer 13 containing lithium metal is disposed on both sides of a negative electrode current collector 11′, a solid electrolyte layer 17, and a positive electrode in which a positive electrode active material layer 15 containing a lithium transition metal composite oxide is disposed on both sides of a positive electrode current collector 11″ are laminated. Specifically, the negative electrode, solid electrolyte layer, and positive electrode are laminated in this order such that one negative electrode active material layer 13 and an adjacent positive electrode active material layer 15 face each other with the solid electrolyte layer 17 interposed therebetween. As a result, adjacent negative electrode, solid electrolyte layer, and positive electrode constitute one unit cell layer 19. Therefore, the stacked secondary battery 10 a shown in FIG. 2 can also be said to have a configuration in which a plurality of unit cell layers 19 are laminated and electrically connected in parallel.

[0018] A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative and positive electrodes) are attached to the negative electrode current collector 11′ and the positive electrode current collector 11″, respectively, and are configured to be sandwiched between the ends of the laminate film 29 and led out of the laminate film 29. The negative electrode current collector 25 and the positive electrode current collector 27 may be attached to the negative electrode current collector 11′ and the positive electrode current collector 11″ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via a negative electrode terminal lead and a positive electrode terminal lead (not shown), respectively, as necessary.

[0019] FIG. 3 is an enlarged cross-sectional view of a cell layer 19 of a stacked secondary battery according to one embodiment of the present invention. As shown in FIG. 3 , the cell layer 19 constituting the stacked secondary battery 10 a according to this embodiment has a positive electrode composed of a positive electrode current collector 11″ and a positive electrode active material layer 15 disposed on the surface thereof. A solid electrolyte layer 17 containing a solid electrolyte is disposed on the surface of the positive electrode active material layer 15 opposite the positive electrode current collector 11″. In the embodiment shown in FIG. 3 , the outer peripheral edge of the solid electrolyte layer 17 extends all the way to the side surface of the positive electrode active material layer 15. As a result, the positive electrode active material layer 15 is configured to be slightly smaller than the solid electrolyte layer 17. In other words, when the power generating element 21 is viewed from above, the entire outer periphery of the positive electrode active material layer 15 is positioned inside the outer periphery of the solid electrolyte layer 17. With this configuration, even if the lithium metal constituting the negative electrode active material layer 13 is pushed out from the outer peripheral edge of the solid electrolyte layer 17 toward the positive electrode active material layer 15 due to the restraining pressure of the pressure member, the lithium metal is less likely to come into contact with the side surface of the positive electrode active material layer 15. As a result, the effect of preventing short circuits is further enhanced. Note that the "side surface of the positive electrode active material layer" refers to the surface of the positive electrode active material layer that is not in contact with the positive electrode current collector and does not face the negative electrode current collector.

[0020] In the embodiment shown in FIG. 3, the intensity ratio R(I Ｇ / I ＤA graphene layer 18 (carbon particle layer) containing graphene particles with a relatively large intensity ratio R is provided (details of the intensity ratio R will be described later). The presence of this graphene layer 18 (carbon particle layer) on the surface of the negative electrode current collector 11′ improves the contact between the lithium metal serving as the negative electrode active material layer 13 and the negative electrode current collector 11′ and the diffusibility of lithium ions in the surface direction. As a result, even during a high-rate charging process such as rapid charging, uniform deposition of the lithium metal serving as the negative electrode active material layer 13 is possible, and sufficient battery performance can be maintained. Therefore, it can be said that the graphene layer 18 (carbon particle layer) functions as a lithium diffusion layer.

[0021] Furthermore, a carbon black layer 22 containing carbon black nanoparticles is provided on the entire main surface of the solid electrolyte layer 17 facing the negative electrode current collector 11′ and on the entire side surface of the solid electrolyte layer 17. The carbon black constituting this carbon black layer 22 has lithium ion conductivity, and therefore the carbon black layer 22 can conduct lithium ions. Therefore, the provision of the carbon black layer 22 does not impede the progress of the battery reaction. The carbon black layer 22 also functions to suppress the reaction between the lithium metal (negative electrode active material layer 13) deposited on the negative electrode current collector 11′ and the solid electrolyte contained in the solid electrolyte layer 17 during charging. Therefore, the carbon black layer 22 can be said to function as an ion-conductive reaction suppression layer. Note that the "side surface of the solid electrolyte layer" refers to the surface of the solid electrolyte layer that does not face either the positive electrode active material layer or the negative electrode current collector during discharging when the negative electrode active material layer 13 made of lithium metal is not present. By disposing such carbon black layer 22 also on the side surface of solid electrolyte layer 17, even when lithium metal deposited on the surface of negative electrode current collector 11′ during charging is pushed out from the outer peripheral edge of solid electrolyte layer 17 by the restraining pressure of the pressing member, contact between solid electrolyte layer 17 and negative electrode active material layer 13 is prevented. In addition, the effective area of ​​lithium metal facing positive electrode active material layer 15 via carbon black layer 22 and solid electrolyte layer 17 becomes larger, which has the advantage of further improving charge / discharge efficiency.

[0022] In the embodiment shown in FIG. 3 , a magnesium layer 23 containing a magnesium salt is provided on the entire main surface of the carbon black layer 22 facing the negative electrode current collector 11′. The presence of this magnesium layer 23 has the advantage of further improving high-rate characteristics (resistance to rapid charging). This is thought to be because the magnesium layer 23 interposed between the carbon black layer 22 and the negative electrode current collector 11′ can reduce the energy required for lithium ions to precipitate as lithium metal during the charging process, thereby enabling charge and discharge at a higher current density. Therefore, it can be said that the magnesium layer 23 functions as a lithium deposition energy reducing layer.

[0023] In the stacked secondary battery 10a according to this embodiment, the power generating element 21 sealed in the laminate film 29 shown in FIG. 1 is preferably sandwiched between two plate-shaped members and further fastened using a fastening member. As a result, the plate-shaped members and fastening members function as pressure members that pressurize (restrain) the power generating element 21 in the stacking direction. Examples of the plate-shaped members include metal plates and resin plates. Examples of the fastening members include bolts and nuts. However, the pressure members are not particularly limited as long as they can pressurize the power generating element 21 in the stacking direction. A typical pressure member is a combination of a plate made of a rigid material, like the plate-shaped members, and the fastening members described above. Furthermore, the fastening members may be not only bolts and nuts, but also tension plates or the like that secure the ends of the plate-shaped members so as to restrain the power generating element 21 in the stacking direction. The lower limit of the load applied to the power generating element 21 (constraint pressure in the stacking direction of the power generating element) is, for example, 0.1 MPa or more, preferably 1 MPa or more, more preferably 3 MPa or more, and even more preferably 5 MPa or more. The upper limit of the constraint pressure in the stacking direction of the power generating element is, for example, 100 MPa or less, preferably 70 MPa or less, more preferably 40 MPa or less, and even more preferably 10 MPa or less.

[0024] The main components of the stacked secondary battery 10a will be described below.

[0025] [Positive Electrode Current Collector] The positive electrode current collector is a conductive member that functions as a flow path for electrons that are released from the positive electrode toward an external load or flow from a power source toward the positive electrode as the battery reaction (charge / discharge reaction) progresses. There are no particular limitations on the material that constitutes the positive electrode current collector. For example, metals and conductive resins can be used as the material for the positive electrode current collector. There are no particular limitations on the thickness of the positive electrode current collector, but an example is 10 to 100 μm.

[0026] [Positive Electrode Active Material Layer] The positive electrode constituting the lithium secondary battery according to this embodiment has a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions.

[0027] The positive electrode active material is not particularly limited as long as it can release lithium ions during the charging process of the secondary battery and can absorb lithium ions during the discharging process. ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ Among these, a composite oxide containing lithium and nickel is preferably used, and Li(Ni—Mn—Co)O is more preferably used. ２Also, those in which some of these transition metals have been replaced with other elements (hereinafter also simply referred to as "NMC composite oxides") are used. NMC composite oxides have a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co) atomic layers (orderly arranged) are alternately stacked with oxygen atomic layers interposed therebetween, and contain one Li atom per transition metal M atom, so that the amount of Li that can be extracted is twice that of spinel lithium manganese oxides, i.e., the supply capacity is doubled, and high capacity can be achieved.

[0028] As described above, the NMC composite oxide also includes composite oxides in which a portion of the transition metal element is substituted with another metal element. In this case, the other element may be Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, or Zn, preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, or Cr, more preferably Ti, Zr, P, Al, Mg, or Cr, and even more preferably Ti, Zr, Al, Mg, or Cr from the viewpoint of improving cycle characteristics.

[0029] Furthermore, in one preferred embodiment, a sulfur-based positive electrode active material is used. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0030] In some cases, two or more positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used.

[0031] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle size (D50) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even 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 average particle size (D50) can be measured by a laser diffraction scattering method.

[0032] 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 30 to 99 mass %, more preferably in the range of 40 to 90 mass %, and even more preferably in the range of 45 to 80 mass %.

[0033] In the lithium secondary battery according to this embodiment, the positive electrode active material layer 15 preferably further contains a solid electrolyte. Examples of the solid electrolyte include a sulfide solid electrolyte, a resin solid electrolyte, and an oxide solid electrolyte. In this specification, the term "solid electrolyte" refers to a material mainly composed of an ion conductor capable of conducting ions in a solid state, and in particular, a material having a lithium ion conductivity of 1×10 at room temperature (25° C.). −５ S / cm or more, and this lithium ion conductivity is preferably 1×10 −４ The ionic conductivity is 200 S / cm or more. Here, the value of the ionic conductivity can be measured by an AC impedance method.

[0034] In another preferred embodiment of the secondary battery according to the present aspect, the solid electrolyte is preferably a sulfide solid electrolyte containing an S element, from the viewpoint of exhibiting excellent lithium ion conductivity and being able to better follow the volume change of the electrode active material that accompanies charge and discharge, more preferably a sulfide solid electrolyte containing a Li element, an M element, and an S element, wherein the M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I, and even more preferably a sulfide solid electrolyte containing an S element, a Li element, and a P element.

[0035] The sulfide solid electrolyte is Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a framework include LiI-Li ３ P.S. ４, LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ In addition, Li ４ P ２ S ７ Examples of sulfide solid electrolytes having a skeleton include Li-P-S solid electrolytes called LPS. （４−ｘ） Ge （１−ｘ） P ｘ S ４ (x satisfies 0<x<1) or the like. More specifically, for example, LPS (Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S., Li. ３．２５ Ge ０．２５ P ０．７５ S ４ , Li １０ GeP ２ S １２ , or Li ６ P.S. ５ X (wherein X is Cl, Br or I). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions. Among them, the sulfide solid electrolyte is preferably LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (wherein X is Cl, Br or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li ３P.S. ４ is selected from the group consisting of:

[0036] The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but is preferably in the range of 1 to 70 mass %, more preferably in the range of 10 to 60 mass %, and even more preferably in the range of 20 to 55 mass %.

[0037] The positive electrode active material layer may further contain at least one of a conductive additive and a binder in addition to the positive electrode active material and the solid electrolyte. The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is preferably within a range of 0.1 to 1000 μm, and more preferably 40 to 100 μm.

[0038] [Solid Electrolyte Layer] The solid electrolyte layer is a layer interposed between the positive electrode active material layer and the negative electrode current collector, and contains a solid electrolyte (usually as a main component). The specific form of the solid electrolyte contained in the solid electrolyte layer is the same as that described above, and therefore detailed description thereof will be omitted here.

[0039] The content of the solid electrolyte in the solid electrolyte layer is, for example, preferably in the range of 10 to 100 mass%, more preferably in the range of 50 to 100 mass%, and even more preferably in the range of 90 to 100 mass%, relative to the total mass of the solid electrolyte layer.

[0040] The solid electrolyte layer may further contain a binder in addition to the above-mentioned solid electrolyte.

[0041] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is preferably within the range of 0.1 to 1000 μm, and more preferably 10 to 40 μm.

[0042] [Negative electrode current collector] The negative electrode current collector is a conductive member that functions as a flow path for electrons that are released from the negative electrode toward the power source as the battery reaction (charge / discharge reaction) progresses, or that flow from an external load toward the negative electrode. There are no particular limitations on the material that constitutes the negative electrode current collector. For example, metals and conductive resins can be used as the material that constitutes the negative electrode current collector. There are no particular limitations on the thickness of the negative electrode current collector, but an example is 10 to 100 μm.

[0043] [Negative Electrode Active Material Layer] The lithium secondary battery according to this embodiment is a so-called lithium deposition type in which lithium metal is deposited on the negative electrode current collector during the charging process. The layer of lithium metal deposited on the negative electrode current collector during this charging process is the negative electrode active material layer of the lithium secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. Although the negative electrode active material layer does not need to be present during full discharge, in some cases, a negative electrode active material layer composed of a certain amount of lithium metal may be present during full discharge. Furthermore, the thickness of the negative electrode active material layer (lithium metal layer) during full charge is not particularly limited, but is typically 0.1 to 1000 μm.

[0044] [Carbon Particle Layer] In the lithium secondary battery according to this embodiment, a carbon particle layer containing carbon particles is disposed on at least a part of the region of the main surface of the negative electrode current collector facing the solid electrolyte layer, where the positive electrode active material layer faces the negative electrode current collector. Here, the carbon particle layer has a G-band peak intensity (I Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ ) is 7 or more.

[0045] Generally, when carbon materials are analyzed by Raman spectroscopy, the −１ Near and 1582 cm −１ Highly crystalline carbon materials such as graphene and graphite have a peak at 1582 cm −１On the other hand, as the crystallinity decreases (the number of crystal structure defects increases), a strong peak appears around 1350 cm −１ This peak is usually called the "D band" (the diamond peak is strictly at 1333 cm −１ and is distinguished from the D band.) G band peak intensity (I Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ ) is used as an index of the degree of crystallinity of the carbon material. Ｇ / I Ｄ The intensity ratio R can be calculated by measuring the Raman spectrum of the carbon particles contained in the carbon particle layer using a micro-Raman spectrometer. When the carbon particle layer contains carbon particles with different intensity ratios R, the intensity ratio R can be calculated as a weighted average of the intensity ratios R weighted by the mass of each type of carbon particle.

[0046] As described above, in this embodiment, it is essential that the intensity ratio R of the carbon particles contained in the carbon particle layer is 7 or more. In a preferred embodiment, the intensity ratio R of the carbon particles contained in the carbon particle layer is 25 or more, more preferably 50 or more, even more preferably 500 or more, still more preferably 2000 or more, particularly preferably 5000 or more, and most preferably 8000 or more. There is no particular restriction on the upper limit of the intensity ratio R, but it is usually 100,000 or less.

[0047] The carbon material constituting the carbon particles contained in the carbon particle layer can be used without any particular limitation as long as it exhibits the intensity ratio R described above. Among these, carbon materials that exhibit a particularly high intensity ratio R include carbon materials formed of graphene layers. While there are no particular limitations on the number of stacked graphene layers constituting these carbon materials, in this specification, a scaly carbon material having up to 10 stacked graphene layers will be referred to as "graphene." Furthermore, graphene having one stacked graphene layer will be referred to as "single-layer graphene," and graphene having 2 to 10 stacked graphene layers will be referred to as "multilayer graphene." Furthermore, a scaly carbon material having 11 or more stacked graphene layers will be referred to as "graphite." Here, as an example, the number of stacked graphene layers constituting the carbon material is preferably 1 to 100 layers, more preferably 2 to 50 layers, even more preferably 3 to 20 layers, and particularly preferably 4 to 10 layers. Therefore, the carbon particles contained in the carbon particle layer according to this embodiment preferably contain graphene or graphite, and more preferably contain graphene. Graphene or graphite (particularly graphene) is a highly crystalline carbon material, as indicated by a high intensity ratio R. Therefore, it can effectively contribute to improving the contact between the lithium metal serving as the negative electrode active material layer and the negative electrode current collector, and the in-plane diffusion of lithium ions. The carbon particles contained in the carbon particle layer may be of one type alone or two or more types in combination. Other carbon materials include, for example, carbon black, diamond (e.g., boron-doped), fullerene, carbon nanotube, carbon nanofiber (vapor-grown carbon fiber (VGCF), etc.), carbon nanohorn, carbon microcoil, and carbon nanocoil. Commercially available carbon particles, processed products of commercially available products, or homemade carbon particles may be used. The manufacturing methods for the above-described multilayer graphene and graphite are widely known, and therefore will not be described in detail here. However, as an example, the intensity ratio R can be controlled by changing the calcination temperature of graphite, which is the precursor used to prepare the carbon particles.

[0048] The content of carbon particles in the carbon particle layer is not particularly limited, but is preferably 50 to 100% by mass, more preferably 80 to 99% by mass, and even more preferably 90 to 98% by mass, relative to 100% by mass of the total amount of the constituent components of the carbon particle layer.

[0049] The carbon particle layer according to this embodiment may contain a binder in addition to the carbon particles. Examples of the binder include 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, 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 product, styrene-isoprene-styrene block copolymer and its hydrogenated product, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PC), and the like. fluororesins such as vinylidene fluoride-hexafluoropropylene-based fluororubbers (VDF-HFP-based fluororubbers), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-HFP-TFE-based fluororubbers), vinylidene fluoride-pentafluoropropylene-based fluororubbers (VDF-PFP-based fluororubbers), Examples of the fluororubber include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubbers (VDF-PFP-TFE-based fluororubbers), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubbers (VDF-PFMVE-TFE-based fluororubbers), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers), and epoxy resins.Among these, polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferably used.

[0050] The content of the binder in the carbon particle layer is not particularly limited, but is preferably 50% by mass or less, more preferably 1 to 20% by mass, and even more preferably 2 to 10% by mass, relative to 100% by mass of the total amount of the constituent components of the carbon particle layer.

[0051] There are no particular limitations on the average thickness of the carbon particle layer, as long as it is disposed at a thickness that allows the above-mentioned functions to be exhibited. As an example, the average thickness of the carbon particle layer is preferably 10 nm to 10 μm, more preferably 50 nm to 6 μm, and even more preferably 1 to 4 μm. The "average thickness" of the carbon particle layer refers to a value calculated as the arithmetic mean value of thickness measurements taken at several to several dozen different locations on the carbon particle layer.

[0052] Of the carbon particles contained in the carbon particle layer, the proportion of particles whose major axes are oriented in the plane direction of the carbon particle layer is preferably 80% or more, more preferably 85% or more, particularly preferably 90% or more, and most preferably 95% or more (the upper limit is 100%). Such plane-oriented carbon particle orientation can further improve the plane-direction diffusivity of lithium ions. The above proportion is calculated by the method described in the Examples section below (observation of cross-sectional images using a scanning electron microscope (SEM)).

[0053] Furthermore, the surface roughness (maximum height defined in JIS B 0601-2001; Rz) of the main surface of the carbon particle layer facing the solid electrolyte layer is preferably 15 μm or less, more preferably 12 μm or less, particularly preferably 10 μm or less, and most preferably 8 μm or less. When the maximum height (Rz) of the surface of the carbon particle layer is within this range, local current concentration is less likely to occur during charge and discharge. As a result, the contact between the lithium metal as the negative electrode active material layer and the negative electrode current collector can be further improved.

[0054] Furthermore, the peel strength of the carbon particle layer with the negative electrode current collector is preferably 5 N / m or more, more preferably 10 N / m or more, and even more preferably 15 N / m or more. When the peel strength of the carbon particle layer with the negative electrode current collector is within this range, lithium metal is less likely to deposit at the interface between the carbon particle layer and the negative electrode current collector during charging, and lithium metal can be reliably deposited at the interface between the carbon particle layer and the solid electrolyte layer, thereby further enhancing the effect of improving rapid charging characteristics.

[0055] The carbon particle layer may be disposed on the entire surface of the negative electrode current collector as shown in Fig. 3, or may be disposed on a part of the surface of the negative electrode current collector. Even if the size of the current collector becomes larger than that shown in Fig. 3 depending on the design of the current collector structure, the carbon particle layer can be efficiently utilized by providing the carbon particle layer only in the area where lithium metal is desired to be deposited (part of the surface of the negative electrode current collector).

[0056] When the power generating element is viewed in a plane in the stacking direction, the relationship between the size of the carbon particle layer and the size of the solid electrolyte layer is not particularly limited. However, as shown in Fig. 3 , when the power generating element is viewed in a plane, the outer peripheral edge of the carbon particle layer (graphene layer 18) is preferably located inside the outer peripheral edge of the solid electrolyte layer 17. This configuration effectively prevents lithium metal deposited during charging from bypassing the outer peripheral edge of the solid electrolyte layer and short-circuiting with the positive electrode active material layer.

[0057] The method for forming the carbon particle layer on the surface of the negative electrode current collector is not particularly limited. For example, a method can be used in which a slurry prepared by dispersing the carbon particles and, if necessary, a binder in an appropriate solvent is applied to the surface of the negative electrode current collector, and the solvent is then dried. Alternatively, the slurry can be applied to the surface of a support such as stainless steel foil, the solvent is dried, and the resulting coating is bonded to the surface of the negative electrode current collector using a method such as hydrostatic pressing, and then the support is peeled off. To control the in-plane orientation, surface roughness (maximum height Rz), and peel strength of the carbon particle layer within the ranges of the preferred embodiment, it is effective to form the carbon particle layer on the surface of the negative electrode current collector using the above-described method, and then subject the resulting laminate to a rolling process using a roll press. Details of the rolling process using a roll press are omitted, but the various parameters described above can be appropriately controlled by adjusting the pressing pressure (linear pressure), the number of times the process is performed, and the compounding ratio of the carbon particles to the binder during the rolling process.

[0058] [Ion-Conductive Reaction-Inhibiting Layer] In the lithium secondary battery according to this embodiment, as shown in FIG. 3 , an ion-conductive reaction-inhibiting layer (carbon black layer 22) is preferably provided on at least a portion of the region of the main surface of the solid electrolyte layer 17 facing the negative electrode current collector 11′, where the positive electrode active material layer 15 faces the negative electrode current collector 11′. This ion-conductive reaction-inhibiting layer has lithium ion conductivity and inhibits the reaction between lithium metal (negative electrode active material layer) and the solid electrolyte. Therefore, by providing the ion-conductive reaction-inhibiting layer, it is possible to prevent degradation of the solid electrolyte and a decrease in battery capacity caused by the reaction between lithium metal (negative electrode active material layer) and the solid electrolyte without impeding the progress of the battery reaction.

[0059] Here, a material "has lithium ion conductivity" means that the lithium ion conductivity of the material at 25°C is 1×10 −４ On the other hand, when a material "does not have lithium ion conductivity," it means that the lithium ion conductivity of the material at 25°C is 1 × 10 −４In the lithium secondary battery according to the present embodiment, the lithium ion conductivity of the constituent material of the ion-conductive reaction suppression layer at 25° C. is less than 1×10 −４ [S / cm] or more, preferably 1.5 × 10 −４ [S / cm] or more, more preferably 2.0 × 10 −４ [S / cm] or more, and more preferably 2.5 × 10 −４ [S / cm] or more, and particularly preferably 3.0 × 10 −４ [S / cm] or more.

[0060] The constituent material of the ion-conductive reaction suppression layer is not particularly limited, and various materials capable of exhibiting the above-mentioned functions can be employed. One example of a constituent material of the ion-conductive reaction suppression layer is nanoparticles having lithium ion conductivity (herein, nanoparticles as a constituent material of the ion-conductive reaction suppression layer are also simply referred to as "first nanoparticles"). By including the first nanoparticles in the ion-conductive reaction suppression layer, a lithium secondary battery with particularly excellent ion-conductive reaction suppression layer functionality can be provided. Here, "nanoparticles" refers to particles having an average particle diameter on the nanometer (nm) scale. The "average particle diameter" of nanoparticles refers to the 50% cumulative diameter (D50) of the particle diameter (the maximum distance between any two points on the outline of the observed particle) measured by observing the cross section of a layer containing the nanoparticles with a scanning electron microscope (SEM). The average particle diameter of the first nanoparticles is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 150 nm or less, particularly preferably 100 nm or less, and most preferably 60 nm or less. In particular, when the average particle size of the first nanoparticles is 60 nm or less, a lithium secondary battery having a particularly excellent dendrite growth suppression effect can be provided. Note that there is no particular limit on the lower limit of the average particle size of the first nanoparticles, but it is usually 10 nm or more, and preferably 20 nm or more.

[0061] From the viewpoint of particularly excellent function as an ion-conductive reaction suppression layer, such first nanoparticles preferably contain one or more elements selected from the group consisting of carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, and more preferably comprise one or more of these elements as simple substances or alloys. Furthermore, the first nanoparticles preferably contain carbon, and more preferably comprise simple carbon. Examples of such materials comprised of simple carbon include acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen Black (registered trademark), carbon nanotubes, carbon nanohorns, carbon nanoballoons, and fullerenes. When the ion-conductive reaction suppression layer contains such nanoparticles, the layer may further contain a binder.

[0062] There are no particular limitations on the method for forming the ion-conductive reaction suppression layer containing the first nanoparticles described above on the surface of the solid electrolyte layer facing the negative electrode current collector. For example, a method can be used in which a slurry containing the nanoparticles and, if necessary, a binder dispersed in an appropriate solvent is applied to the surface of the solid electrolyte layer facing the negative electrode current collector, and the solvent is then dried. Alternatively, the slurry can be applied to the surface of a support such as stainless steel foil, the solvent is dried, and the resulting coating is bonded to the surface of the solid electrolyte layer facing the negative electrode current collector using a method such as a hydrostatic press, and the support is then peeled off to form the ion-conductive reaction suppression layer. In some cases, the ion-conductive reaction suppression layer can be formed by forming a continuous layer containing any of the above-mentioned materials by a method such as sputtering, rather than in the form of nanoparticles.

[0063] The first nanoparticles as the constituent material of the ion-conductive reaction-suppressing layer have been described above, but the ion-conductive reaction-suppressing layer containing the first nanoparticles described above usually has electronic conductivity. If the ion-conductive reaction-suppressing layer has electronic conductivity, it is preferable because it can further improve the resistance to rapid charging.

[0064] However, it is also a preferred embodiment that the ion-conductive reaction suppression layer is electronically insulating. When the ion-conductive reaction suppression layer is electronically insulating, it has high stability at lower potentials, and therefore can more reliably prevent side reactions between the solid electrolyte layer and lithium metal compared to when the ion-conductive layer is electronically conductive, which can effectively contribute to improving the durability of the cell. Examples of electronically insulating constituent materials for the ion-conductive reaction suppression layer include lithium halides (lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI)), composite metal oxides represented by Li-M-O (wherein M is one or more metal elements selected from the group consisting of Mg, Au, Al, Sn, and Zn), and Li-Ba-TiO ３ Examples of suitable lithium-containing compounds include one or more lithium-containing compounds selected from the group consisting of composite oxides. All of these materials are more stable than solid electrolytes with respect to reductive decomposition upon contact with lithium metal. That is, when comparing the tendency of the solid electrolyte constituting the solid electrolyte layer to undergo reductive decomposition upon contact with lithium metal with the tendency of the lithium-containing compound constituting the ion-conductive reaction suppression layer to undergo reductive decomposition upon contact with lithium metal, the latter tendency is smaller. Therefore, the lithium-containing compound can also function as an ion-conductive reaction suppression layer. There are no particular limitations on the method for forming the ion-conductive reaction suppression layer containing such a lithium-containing compound. For example, the ion-conductive reaction suppression layer can be formed by forming a continuous layer containing the lithium-containing compound by a method such as sputtering.

[0065] The average thickness of the ion-conductive reaction suppression layer is not particularly limited, as long as it is disposed at a thickness that allows the above-described functions to be exhibited. For example, when the ion-conductive reaction suppression layer is a layer containing first nanoparticles, the average thickness is preferably 300 nm to 20 μm, more preferably 500 nm to 15 μm, and even more preferably 1 to 10 μm. Furthermore, when the layer is a continuous layer made of a lithium-containing compound formed by a technique such as sputtering, the average thickness is preferably 0.5 to 20 nm. The "average thickness" of the ion-conductive reaction suppression layer refers to the value calculated as the arithmetic mean value of thickness measurements taken at several to several dozen different locations on the ion-conductive reaction suppression layer constituting a lithium secondary battery.

[0066] The Young's modulus of the ion-conductive reaction suppression layer is preferably 2 GPa or more, more preferably 5 GPa or more, particularly preferably 8 GPa or more, and particularly preferably 10 GPa or more. When the ion-conductive reaction suppression layer exhibits such a high Young's modulus, even if dendrites are generated from lithium metal precipitated during rapid charging, the occurrence of an internal short circuit due to the dendrites penetrating the solid electrolyte layer and reaching the positive electrode active material layer can be effectively prevented. The Young's modulus value of the ion-conductive reaction suppression layer is a value measured in accordance with JIS K 7161-1:2014.

[0067] [Lithium Deposition Energy Reduction Layer] In the lithium secondary battery according to this embodiment, as shown in FIG. 3 , a lithium deposition energy reduction layer (magnesium layer 23) containing an element capable of alloying with lithium or a compound containing such an element is preferably further provided on at least a portion (preferably the entire surface) of the principal surface of the ion-conductive reaction suppression layer (carbon black layer 22) facing the negative electrode current collector 11′. With this configuration, when lithium metal precipitates as the negative electrode active material layer during charging of the lithium secondary battery, the constituent material of the lithium deposition energy reduction layer alloys with lithium, thereby reducing the energy required for lithium metal to precipitate as the negative electrode active material layer, enabling charge / discharge at a higher current density. As a result, the charge capacity can be further improved even during rapid charging. Here, the element capable of alloying with lithium contained in the lithium deposition energy reduction layer can be at least one selected from the group consisting of gold, silver, zinc, magnesium, aluminum, platinum, silicon, tin, bismuth, indium, and palladium. The lithium deposition energy reducing layer may be composed of these elements alone or compounds containing these elements. Examples of such compounds include salts such as chlorides, sulfates, carbonates, and nitrates, as well as SiO ｘ and SnO ｘ and alloys containing transition metal elements such as Ni-Si alloys, Ti-Si alloys, Mg-Sn alloys, Fe-Sn alloys, etc. Among these, it is preferable to contain the above elements as simple substances or salts of the elements, and it is more preferable to contain silver, zinc, or magnesium as simple substances or salts of the elements.

[0068] The average thickness of the lithium precipitation energy reduction layer is not particularly limited, as long as it is disposed at a thickness that allows the above-mentioned functions to be exhibited. As an example, the average thickness of the lithium precipitation energy reduction layer is preferably 10 nm to 10 μm, more preferably 50 nm to 6 μm, and even more preferably 1 to 4 μm. The "average thickness" of the lithium precipitation energy reduction layer refers to a value calculated as the arithmetic average of thicknesses measured at several to several dozen different locations on the lithium precipitation energy reduction layer.

[0069] Although the above description has been given using an example in which the secondary battery according to the present embodiment is an all-solid-state lithium secondary battery, the lithium secondary battery according to the present 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 (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount be such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur. Note that the liquid electrolyte (electrolytic solution) is a solution in the form of a conventionally known lithium salt dissolved in a conventionally known organic solvent. The liquid electrolyte (electrolytic solution) may further contain additives other than the organic solvent and the lithium salt. These additives may be used alone or in combination of two or more. Furthermore, when an additive is used in the electrolyte solution, the amount used can be adjusted as appropriate.

[0070] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the following operations were carried out in a glove box with an argon atmosphere at a dew point of −68° C. or less. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0071] <Examples of Preparation of Evaluation Cell> [Example 1] (Preparation of Positive Electrode Active Material Layer) As a constituent material of the positive electrode active material layer, NMC composite oxide (LiNi ０．８ Mn ０．１ Co ０．１ O ２, average particle size (D50): 3 μm) and an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ The following materials were prepared: carbon nanofiber (CNF) (VGCF (registered trademark), aspect ratio: 60, average fiber diameter: approximately 150 nm, average fiber length: approximately 9 μm, manufactured by Showa Denko K.K.) as a conductive additive; and polytetrafluoroethylene (PTFE) as a binder. In a glove box with an argon atmosphere and a dew point of −68°C or lower, the positive electrode active material, solid electrolyte, conductive additive, and binder were weighed out to a mass ratio of 79:16:3:2 and kneaded in an agate mortar. After confirming that the binder had fibrillated, the resulting mixture was formed into a sheet using a hand roller and then punched into a 19 mm square to obtain a 100 μm-thick positive electrode active material layer.

[0072] (Preparation of solid electrolyte layer) Argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ A solid electrolyte slurry was prepared by mixing 95 parts by mass of styrene-butadiene rubber (SBR) as a binder with 5 parts by mass of mesitylene as a solvent. The obtained solid electrolyte slurry was applied to the surface of a stainless steel foil as a support using an applicator, dried, and then punched out into a 25 mm square to obtain a 30 μm-thick solid electrolyte layer.

[0073] (Preparation of Negative Electrode) 95 parts by mass of graphene as carbon particles and a binder solution (5 parts by mass of polyvinylidene fluoride (PVdF) as a binder dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent) were mixed to prepare a carbon particle slurry (solid content 5% by mass). The obtained carbon particle slurry was applied to the surface of stainless steel foil (thickness 10 μm) as a negative electrode current collector using an applicator and dried to obtain a laminate. Thereafter, the obtained laminate was rolled using a roll press to form the laminate into a sheet, which was punched into a square of 21 mm square, to obtain a negative electrode in which a carbon particle layer was laminated on the surface of the negative electrode current collector. In this example, the conditions for the roll press were set so that the thickness of the carbon particle layer was 100 nm. Furthermore, the G-band peak intensity (I Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ Specifically, first, the Raman spectrum of the carbon particles was measured using a microscopic Raman spectrometer. −１ (1582 cm −１ The peak intensity (I Ｇ ) and 1300-1400 cm −１ (1350 cm −１ The peak intensity (I Ｄ ) and the peak area ratio (I Ｇ / I Ｄ ) was calculated and designated as the intensity ratio R (the same applies below). As a result, the intensity ratio R of the carbon particles was 8223.

[0074] (Preparation of Evaluation Cell) The positive electrode active material layer and the solid electrolyte layer prepared above were sequentially stacked on an aluminum foil (19 mm square, 20 μm thick) serving as a positive electrode current collector. The stainless steel foil supporting the solid electrolyte layer was peeled off, and the stack was pressed by cold isostatic pressing (CIP) to obtain a laminate consisting of a positive electrode current collector / positive electrode active material layer / solid electrolyte layer. The pressing pressure during the CIP treatment was controlled so that the outer peripheral edge of the solid electrolyte layer extended partway along the side of the positive electrode active material layer. Next, an ion-conductive reaction suppression layer (100 nm thick) made of lithium chloride (LiCl) was formed on the exposed surface of the solid electrolyte layer by sputtering, thereby obtaining a laminate consisting of a positive electrode current collector / positive electrode active material layer / solid electrolyte layer / ion-conductive reaction suppression layer. The sputtering conditions were controlled so that the outer peripheral edge of the ion-conductive reaction suppression layer extended partway along the side of the solid electrolyte layer. The Young's modulus of the resulting ion-conductive reaction suppression layer (LiCl layer) was measured by spherical nanoindentation measurement and found to be 30 GPa.

[0075] Thereafter, the negative electrode prepared above was stacked on the ion-conductive reaction-suppressing layer so that the exposed surface of the carbon particle layer faced the ion-conductive reaction-suppressing layer, and the stack was pressed by cold isostatic pressing (CIP) to prepare an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery).

[0076] [Example 2] Except for using graphite (intensity ratio R = 26) instead of graphene as the carbon particles constituting the carbon particle layer, an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) of this example was fabricated in the same manner as in Example 1. In this example, the conditions for the roll press were set so that the thickness of the carbon particle layer would be 3 μm.

[0077] [Example 3] Except for using graphite (intensity ratio R = 7) instead of graphene as the carbon particles constituting the carbon particle layer, an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) of this example was produced in the same manner as in Example 1. In this example, the conditions for the roll press were set so that the thickness of the carbon particle layer would be 3 μm.

[0078] Example 4: In Example 1, a carbon black layer was used as the ion-conductive reaction suppression layer instead of the lithium chloride sputtering layer. Specifically, 90 parts by mass of carbon black was mixed with a binder solution (10 parts by mass of polyvinylidene fluoride (PVdF) as a binder dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent) to prepare a carbon black slurry (solid content: 5% by mass). The resulting carbon black slurry was applied to the surface of a stainless steel foil support using an applicator, dried, and then punched out into a 21 mm square to obtain a 10 μm-thick carbon black layer formed on the support. The Young's modulus of the resulting ion-conductive reaction suppression layer (carbon black layer) was measured by spherical nanoindentation measurement and found to be 2 GPa. The positive electrode active material layer and the exposed surface of the solid electrolyte layer were then sequentially stacked on an aluminum foil (19 mm square) serving as a positive electrode current collector. The stainless steel foil supporting the solid electrolyte layer was then peeled off. The exposed surface of the carbon black layer was then stacked on top of the stack. The stainless steel foil supporting the carbon black layer was then peeled off. The stack was then pressed by cold isostatic pressing (CIP) to obtain a laminate consisting of the positive electrode current collector, the positive electrode active material layer, the solid electrolyte layer, and the ion-conductive reaction-suppressing layer. The pressing pressure during the CIP process was controlled so that the outer peripheral edge of the solid electrolyte layer extended partway along the side surface of the positive electrode active material layer, and so that the outer peripheral edge of the ion-conductive reaction-suppressing layer extended partway along the side surface of the solid electrolyte layer. Except for this, the evaluation cell of this example (lithium deposition-type all-solid-state lithium secondary battery) was fabricated using the same method as in Example 1 described above.

[0079] Example 5 Before bonding the negative electrode to the ion-conductive reaction-suppressing layer, a dispersion of magnesium chloride powder dispersed in an appropriate amount of ethanol was spray-coated onto the exposed surface of the carbon black layer and dried to form a lithium deposition energy reduction layer (thickness 10 nm). The negative electrode and the ion-conductive reaction-suppressing layer were then stacked so that the exposed surface of the lithium deposition energy reduction layer faced the ion-conductive reaction-suppressing layer, and the two were pressed together by cold isostatic pressing (CIP) to produce an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery). Except for this, the evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) of this example was produced using the same method as in Example 1 described above.

[0080] [Comparative Example 1] Except for using graphite (intensity ratio R = 4) instead of graphene as the carbon particles constituting the carbon particle layer, an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) for this comparative example was produced in the same manner as in Example 1. In this comparative example, the conditions for the roll press were set so that the thickness of the carbon particle layer would be 3 μm.

[0081] [Comparative Example 2] An evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) for this comparative example was produced in the same manner as in Comparative Example 1, except that the rolling process using a roll press was not performed when producing the carbon particle layer. The thickness of the obtained carbon particle layer was 7 μm.

[0082] [Comparative Example 3] Except for using carbon black (intensity ratio R = 0.9) instead of graphene as the carbon particles constituting the carbon particle layer, an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) for this comparative example was produced in the same manner as in the above-described comparative example 1. In this comparative example, the conditions for the roll press machine were set so that the thickness of the carbon particle layer would be 7 μm.

[0083] [Evaluation of Negative Electrode] The carbon particle layers of the negative electrodes prepared in the above Examples and Comparative Examples were observed in cross sections in the lamination direction using a scanning electron microscope (SEM). The percentage of carbon particles contained in the carbon particle layer whose major axis was oriented in the plane direction of the carbon particle layer (i.e., whose major axis formed an angle of 45° or less with respect to the plane direction) was measured. The "major axis of the particle" refers to the direction of the line segment that indicates the maximum distance between two parallel lines when the outline of the carbon particle in the SEM cross-sectional image is sandwiched between the lines. As a result, it was confirmed that 80% or more of the carbon particles in the carbon particle layers of Examples 1 to 5 and Comparative Example 1 were oriented in the plane direction. Meanwhile, in the carbon particle layer of Comparative Example 2, although some orientation of the carbon particles in the plane direction was observed, the percentage of carbon particles with an orientation of 45° or less was less than 80%. Furthermore, in the carbon particle layer of Comparative Example 3, the carbon particles were randomly oriented, and no particular orientation was observed.

[0084] Furthermore, the carbon particle layer of the negative electrode prepared above was measured for Rz (maximum height) as defined in JIS B 0601-2001. The results are shown in Table 1 below. Furthermore, the peel strength between the carbon particle layer and the negative electrode current collector was measured for the negative electrode prepared above. Specifically, the negative electrode prepared above was cut into 10 mm wide samples, and the surface on the carbon particle layer side was fixed to a table using double-sided tape. Next, a 90° peel test was performed at a peel rate of 100 mm / min, and the peel strength when the interface between the carbon particle layer and the negative electrode current collector peeled was measured. The results are shown in Table 1 below.

[0085] [Evaluation of Evaluation Cell (Measurement of Charge / Discharge Efficiency)] A positive electrode lead and a negative electrode lead were connected to the positive electrode current collector and the negative electrode current collector of the evaluation cell prepared above, respectively, and charge / discharge was performed at a charge / discharge rate of 0.1 C or 3.5 C according to the following charge / discharge test conditions. During this test, the following charge / discharge test was performed while applying a restraining pressure of 3 MPa in the stacking direction of the evaluation cell using a pressure member.

[0086] (Charge / discharge test conditions) 1) Charging / discharging conditions [Voltage range] 3.0 to 4.3 V [Charging process] CCCV (0.01 C cutoff) [Discharging process] CC [Charge / discharge rate] 0.1 C or 3.5 C (30-minute rest after each charging / discharging) 2) Evaluation temperature: 333 K (60°C).

[0087] The evaluation cell was charged in a constant current / constant voltage (CCCV) mode at the above-mentioned rate from 3.0 V to 4.3 V (0.01 C cutoff) in a thermostatic chamber set at the above-mentioned evaluation temperature using a charge / discharge tester. During the charge process (lithium metal deposition on the negative electrode current collector), the test cell was charged in constant current (CCCV) mode at the above-mentioned rate from 3.0 V to 4.3 V (0.01 C cutoff). During the discharge process (lithium metal dissolution on the negative electrode current collector), the test cell was discharged in constant current (CC) mode at the above-mentioned rate from 4.3 V to 3.0 V. Here, 1 C refers to the current value at which the battery is fully charged (100% charged) after one hour of charging. The charge capacity ratio was calculated as the ratio of the charge capacity at 3.5 C to the charge capacity at 0.1 C as an index of rapid charge characteristics. The results are shown in Table 1 below. After the charge / discharge test, the evaluation cell was visually observed for the location of lithium metal deposition. The results are also shown in Table 1 below.

[0088]

[0089] From the results shown in Table 1, the intensity ratio R(I Ｇ / I Ｄ It can be seen that the 3.5C / 0.1C charge capacity ratio is significantly improved by providing a carbon particle layer having a ρ of 7 or more on the surface of the negative electrode current collector. This demonstrates that the present invention makes it possible to achieve rate characteristics that are compatible with rapid charging in a lithium deposition-type lithium secondary battery.

[0090] Furthermore, a comparison between Example 1, Example 2, and Example 3 reveals that the charge capacity ratio can be significantly improved by using carbon particles having a higher intensity ratio R as the material constituting the carbon particle layer (for example, by using graphene rather than graphite).

[0091] Furthermore, a comparison between Example 1 and Example 4 reveals that the charge capacity ratio can be further improved by using an electronically conductive ion-conductive reaction suppression layer rather than an electronically insulating one.

[0092] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 18 graphene layer (carbon particle layer), 19 unit cell layer, 20 insulating layer, 21 power generating element, 22 carbon black layer (ion conductive reaction suppression layer), 23 magnesium layer (lithium deposition energy reduction layer), 25 negative electrode current collector (negative electrode tab), 27 positive electrode current collector (cathode tab), 29 laminate film.

Claims

a positive electrode including a positive electrode active material layer disposed on a surface of a positive electrode current collector, the positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions; a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; a power generating element having A G-band peak intensity (I) measured by Raman scattering spectroscopy is measured in at least a part of a region of the main surface of the negative electrode current collector that faces the solid electrolyte layer, where the positive electrode active material layer faces the negative electrode current collector. Ｇ ) and D band peak intensity (I Ｄ ) and the intensity ratio R(I Ｇ / I Ｄ ) is 7 or more.

2. The lithium secondary battery according to claim 1, wherein the carbon particle layer contains carbon particles having an intensity ratio R of 50 or more. 　 The lithium secondary battery according to claim 1 or 2, wherein the carbon particles contain graphene.

3. The lithium secondary battery according to claim 1, wherein the ratio of the carbon particles contained in the carbon particle layer whose major axes are oriented in the plane direction of the carbon particle layer is 80% or more.

3. The lithium secondary battery according to claim 1, wherein the surface roughness (maximum height: Rz) of the main surface of the carbon particle layer facing the solid electrolyte layer is 15 μm or less.

3. The lithium secondary battery according to claim 1, wherein the carbon particle layer has a peel strength of 5 N / m or more with respect to the negative electrode current collector.

3. The lithium secondary battery according to claim 1, wherein the carbon particle layer is disposed on a portion of the surface of the negative electrode current collector.

3. The lithium secondary battery according to claim 1, wherein, in a plan view of the power generating element, an outer peripheral edge of the carbon particle layer is located inside an outer peripheral edge of the solid electrolyte layer.

3. The lithium secondary battery according to claim 1, wherein an ion-conductive reaction-suppressing layer having lithium ion conductivity and suppressing a reaction between the lithium metal and the solid electrolyte is provided on at least a part of a region of the main surface of the solid electrolyte layer facing the negative electrode current collector, the region being where the positive electrode active material layer faces the negative electrode current collector. 　 The lithium secondary battery according to claim 9 , wherein the ion-conductive reaction suppression layer has electronic conductivity. 　 The lithium secondary battery according to claim 9 , wherein the ion-conductive reaction suppression layer has electronic insulation properties.

10. The lithium secondary battery according to claim 9, wherein the ion-conductive reaction suppression layer has a Young's modulus of 2 GPa or more.

10. The lithium secondary battery according to claim 9, further comprising a lithium deposition energy reduction layer, the lithium deposition energy reduction layer including an element capable of being alloyed with lithium, or a compound or salt containing the element, on at least a part of a main surface of the ion-conductive reaction-suppressing layer facing the negative electrode current collector.