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

[Technical Field]

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

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to combat global warming. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will help reduce carbon dioxide emissions, and there has been active development of non-aqueous electrolyte secondary batteries, such as secondary batteries for driving motors, which hold the key to putting these vehicles into practical use.

[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, there has been active research and development into all-solid-state lithium secondary batteries that use oxide- or sulfide-based solid electrolytes. Solid electrolytes are materials primarily composed of ionic conductors that allow ionic conduction in a solid state. For this reason, 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 technology 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. Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, in a lithium deposition type lithium secondary battery, a conductive layer is disposed on the main surface of a negative electrode current collector facing a solid electrolyte layer, and a G-band peak intensity (I G ) and D-band peak intensity (I D ) and the intensity ratio R(I G / I DThe 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 having 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 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 containing a solid electrolyte interposed between the positive electrode and the negative electrode. In this lithium secondary battery, a G-band peak intensity (I) measured by Raman scattering spectroscopy is present in at least a portion 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. G ) and D-band peak intensity (I D ) and the intensity ratio R(I G / I D ) is 7 or more. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing the appearance of a flat laminated type all-solid-state lithium secondary battery according to one embodiment of the present invention. [Figure 2] 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. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE 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 ) is 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 laminated type all-solid-state lithium secondary battery (hereinafter also simply referred to as a "laminated 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 laminated 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 to extract 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, 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 such 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 pieces and extended from each side.

[0017] As shown in FIG. 2, during charging, power generating element 21 of stacked secondary battery 10a of this embodiment has a configuration in which a negative electrode in which negative electrode active material layers 13 containing lithium metal are arranged on both sides of negative electrode current collector 11′, a solid electrolyte layer 17, and a positive electrode in which positive electrode active material layers 15 containing lithium transition metal composite oxide are arranged on both sides of positive electrode current collector 11″ are stacked. Specifically, the negative electrode, solid electrolyte layer, and positive electrode are stacked 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 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, stacked secondary battery 10a shown in FIG. 2 can also be said to have a configuration in which a plurality of unit cell layers 19 are stacked 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 extended to the outside 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 10a according to this embodiment has a positive electrode constituted by 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 to the positive electrode current collector 11". Here, in the embodiment shown in FIG. 3, the outer peripheral edge portion of the solid electrolyte layer 17 extends over its entire periphery 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 periphery of the outer peripheral edge of the positive electrode active material layer 15 is configured to be located inside the outer peripheral edge 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 D A 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, so 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 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-like members and further fastened using a fastening member. As a result, the plate-like members and fastening members function as pressure members that pressurize (restrain) the power generating element 21 in the stacking direction. Examples of the plate-like 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-like members, and the fastening members described above. The fastening members may be not only bolts and nuts, but also tension plates that fix the ends of the plate-like 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 (restraint 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 restraint 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 above-described 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 that constitutes 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] [Cathode 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 absorb lithium ions during the discharging process. The type of positive electrode active material is not particularly limited, but layered rock salt active materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, and Li(Ni-Mn-Co)O2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples of oxide active materials include spinel-type active materials such as LiFePO4 and LiMnPO4, olivine-type active materials such as LiFeSiO4 and LiMnSiO4, and Si-containing active materials such as LiFeSiO4 and LiMnSiO4. 12Among these, composite oxides containing lithium and nickel are preferably used, and more preferably Li(Ni-Mn-Co)O2 and those in which some of the transition metals have been replaced with other elements (hereinafter simply referred to as "NMC composite oxides"). NMC composite oxides have a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co) atomic layers are alternately stacked with oxygen atomic layers interposed between them, and contain one Li atom per atom of the transition metal M. The amount of Li that can be extracted is twice that of spinel-based lithium manganese oxides, i.e., the supply capacity is doubled, resulting in high capacity.

[0028] As described above, the NMC composite oxide also includes composite oxides in which a portion of the transition metal element is replaced with another metal element, such as Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, or Zn. Among these, Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, or Cr is preferred, Ti, Zr, P, Al, Mg, or Cr is more preferred, and Ti, Zr, Al, Mg, or Cr is even more preferred 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 sulfide solid electrolytes, resin solid electrolytes, and oxide solid electrolytes. 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 100 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 invention, 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 may have a Li3PS4 skeleton, a Li4P2S7 skeleton, or a Li4P2S6 skeleton. Examples of the sulfide solid electrolyte having a Li3PS4 skeleton include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Further, examples of the sulfide solid electrolyte having a Li4P2S7 skeleton include a Li-P-S-based solid electrolyte called LPS. Further, as the sulfide solid electrolyte, for example, LGPS represented by Li (4-x) Ge (1-x) P x S4 (where x satisfies 0 < x < 1) such as LGPS may be used. More specifically, for example, LPS (Li2S-P2S5), Li7P3S 11 、Li 3.2 P 0.96 S、Li 3.25 Ge 0.25 P 0.75 S4、Li 10 GeP2S 12 or Li6PS5X (where X is Cl, Br, or I), etc. are exemplified. Note that the description of "Li2S-P2S5" means a sulfide solid electrolyte formed using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions. Among them, the sulfide solid electrolyte is preferably LPS (Li2S-P2S5), Li6PS5X (where X is Cl, Br, or I), Li7P3S 11 、Li 3.2 P 0.96 S and Li3PS4, 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 for example, it is preferably within the range of 1 to 70% by mass, more preferably within the range of 10 to 60% by mass, and even more preferably within the range of 20 to 55% by 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, for example, 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 a 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 configuration of the intended lithium secondary battery, but is preferably within the range of 0.1 to 1000 μm, and more preferably 10 to 40 μm, for example.

[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 materials for 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 the present embodiment is a so-called lithium deposition type in which lithium metal is deposited on the negative electrode current collector during charging. The layer of lithium metal deposited on the negative electrode current collector during charging is the negative electrode active material layer of the lithium secondary battery according to the present embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during full discharge, but in some cases, a negative electrode active material layer consisting of a certain amount of lithium metal may be present during full discharge. 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 peak at 1350 cm -1 Near and 1582cm -1 Highly crystalline carbon materials such as graphene and graphite have a peak at around 1582 cm -1 This peak is usually called the "G band". On the other hand, as the crystallinity decreases (the number of crystal structure defects increases), the peak at 1350 cm -1 This peak is usually called the "D band" (the diamond peak is actually at 1333 cm -1 and is distinguished from the D band mentioned above). G band peak intensity (I G ) and D-band peak intensity (I D ) and the intensity ratio R(IG / I D ) is used as an index of the degree of crystallinity of the carbon material. G / I D ) is 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, it 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 upper limit to 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 any carbon material that exhibits the above-described intensity ratio R. 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, for 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 carbon material with high crystallinity, 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, as well as the in-plane diffusion of lithium ions. The carbon particles contained in the carbon particle layer may be of one type, or two or more types may be used 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)), carbon nanohorn, carbon microcoil, and carbon nanocoil. Commercially available carbon particles, processed versions of commercially available carbon particles, or homemade carbon particles may be used. The manufacturing methods for the multilayer graphene and graphite described above 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, the precursor used to prepare the carbon particles.

[0048] There are no particular restrictions on the content of carbon particles in the carbon particle layer, but it is preferably 50 to 100 mass%, more preferably 80 to 99 mass%, and even more preferably 90 to 98 mass%, relative to 100 mass% of the total amount of the constituent components of the carbon particle layer.

[0049] The carbon particle layer according to the present 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 hydrogenated products thereof, styrene-isoprene-styrene block copolymer and hydrogenated products thereof, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), and polychlorotrifluoroethylene (PC). Examples of the fluororesin include 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-perfluoromethylvinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), and vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), 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] There are no particular restrictions on the binder content in the carbon particle layer, but it 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%). By orienting the carbon particles in the plane direction in this way, the diffusibility of lithium ions in the plane direction can be further improved. 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 improving the 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 portion 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 structural design of the current collector, 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 (a portion 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 periphery of the carbon particle layer (graphene layer 18) is preferably located inside the outer periphery of the solid electrolyte layer 17. This configuration effectively prevents lithium metal deposited during charging from bypassing the outer periphery 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 carbon particle layer can be formed by applying the slurry to the surface of a support such as stainless steel foil, drying the solvent, and then laminating the resulting coating to the surface of the negative electrode current collector using a hydrostatic press or other method, followed by peeling off the support. To control the in-plane orientation of the carbon particles, surface roughness (maximum height Rz), peel strength, and other properties 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 suppression layer] In the lithium secondary battery according to this embodiment, as shown in Fig. 3, an ion-conductive reaction-suppressing 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-suppressing layer has lithium ion conductivity and suppresses the reaction between lithium metal (negative electrode active material layer) and the solid electrolyte. Therefore, by providing the ion-conductive reaction-suppressing 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 -4On the other hand, a material "does not have lithium ion conductivity" means that the lithium ion conductivity of the material at 25°C is 1 x 10 -4 In 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 used. One example of a constituent material of the ion-conductive reaction suppression layer is nanoparticles with 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 with 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. Although there is no particular lower limit for the average particle size of the first nanoparticles, it is usually 10 nm or more, and preferably 20 nm or more.

[0061] From the viewpoint of achieving particularly excellent functionality as an ion-conductive reaction suppression layer, the 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. 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 fullerene. 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 hydrostatic pressing, 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 that are the constituent material of the ion-conductive reaction inhibition layer have been described above, but the ion-conductive reaction inhibition layer containing the first nanoparticles described above usually has electronic conductivity. If the ion-conductive reaction inhibition layer has electronic conductivity, it is preferable because it can further improve the resistance to rapid charging.

[0064] However, an electronically insulating ion-conductive reaction suppression layer is also a preferred embodiment. An electronically insulating ion-conductive reaction suppression layer is more stable at lower potentials than an electronically conductive layer, thereby more reliably preventing side reactions between the solid electrolyte layer and lithium metal, and effectively improving the durability of the cell. Examples of electronically insulating materials for the ion-conductive reaction suppression layer include one or more lithium-containing compounds selected from the group consisting of lithium halides (lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI)), composite metal oxides represented by Li-MO (where M is one or more metal elements selected from the group consisting of Mg, Au, Al, Sn, and Zn), and Li-Ba-TiO composite oxides. All of these materials are more stable than solid electrolytes with respect to reductive decomposition upon contact with lithium metal. In other words, 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 above-mentioned 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-mentioned 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 that constitutes 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 dendrites can effectively prevent the occurrence of an internal short circuit caused by the dendrites penetrating the solid electrolyte layer and reaching the positive electrode active material layer. The Young's modulus of the ion-conductive reaction suppression layer is 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 a simple substance of 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 main 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 deposits 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 deposit 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. The lithium-alloyable element contained in the lithium deposition energy reduction layer may 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 reduction layer may be composed of these simple substances or compounds containing these substances. The 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, and Fe-Sn alloys. Among these, it is preferable to contain the above elements alone or salts of the elements, and it is more preferable to contain silver, zinc, or magnesium alone or salts of the elements.

[0068] There are no particular limitations on the average thickness of the lithium deposition energy reduction 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 lithium deposition 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 deposition energy reduction layer refers to a value calculated as the arithmetic mean value of thickness measurements taken at several to several dozen different locations on the lithium deposition energy reduction layer.

[0069] Although the above description has been given taking the case where the secondary battery according to the present embodiment is an all-solid-state lithium secondary battery as an example, 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 is 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, as the liquid electrolyte (electrolytic solution), a solution in the form of a conventionally known lithium salt dissolved in a conventionally known organic solvent is used. 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 appropriately adjusted. [Example]

[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. In the following, the 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] <Example of evaluation cell production> [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 0.1The following materials were prepared: a cathode active material (CNF) (manufactured by Showa Denko K.K., VGCF®, aspect ratio: 60, average fiber diameter: approximately 150 nm, average fiber length: approximately 9 μm), an argyrodite-type sulfide solid electrolyte (LiPSCl, average particle diameter (D50): 0.2 μm), a conductive additive (CNF), and polytetrafluoroethylene (PTFE) as a binder. In a glove box with an argon atmosphere and a dew point of −68°C or lower, the cathode active material, solid electrolyte, conductive additive, and binder were weighed out in 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 cathode active material layer.

[0072] (Preparation of solid electrolyte layer) A solid electrolyte slurry was prepared by mixing 95 parts by mass of an argyrodite-type sulfide solid electrolyte (Li6PS5Cl) as the solid electrolyte with a binder solution (5 parts by mass of styrene-butadiene rubber (SBR) as the binder dissolved in mesitylene as the solvent). The obtained solid electrolyte slurry was applied to the surface of a stainless steel foil 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. The obtained laminate was then rolled using a roll press to form the laminate into a sheet, which was then punched out into a square with a side length of 21 mm 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 micro-Raman spectrometer. -1 (1582cm -1 The peak intensity (I G ) and 1300-1400cm -1 (1350cm -1 The peak intensity (I D ) and the peak area ratio (I G / I D ) was calculated and used 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 cells) 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 process 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, resulting in 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. Furthermore, 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 top of the ion-conductive reaction-suppressing layer with the exposed surface of the carbon particle layer facing the ion-conductive reaction-suppressing layer, and 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 produced in the same manner as in Example 1. In this example, the conditions for the roll press machine 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 machine were set so that the thickness of the carbon particle layer would be 3 μm.

[0078] [Example 4] In Example 1 described above, 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 obtained 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 obtained ion-conductive reaction suppression layer (carbon black layer) was measured by spherical nanoindentation measurement and found to be 2 GPa. The cathode active material layer and the exposed surface of the solid electrolyte layer were then stacked on an aluminum foil (19 mm square) serving as a cathode 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 cathode active material layer and 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 cathode current collector, the cathode active material layer, the solid electrolyte layer, and the ion-conductive reaction-suppressing layer. The pressure during the CIP process was controlled so that the outer peripheral edge of the solid electrolyte layer extended partway along the side of the cathode active material layer, and so that the outer peripheral edge of the ion-conductive reaction-suppressing layer extended partway along the side of the solid electrolyte layer. The evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) of this example 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 suppression layer, a dispersion of magnesium chloride powder in an appropriate amount of ethanol was added to the carbon particle A lithium deposition energy reduction layer (10 nm thick) was formed by spray coating on the exposed surface of the layer and drying. The exposed surface of the lithium deposition energy reduction layer in the negative electrode was then placed on the ion-conductive reaction-suppressing layer so that it faced the ion-conductive reaction-suppressing layer, and the two were pressed by cold isostatic pressing (CIP) to produce an evaluation cell (a lithium deposition-type all-solid-state lithium secondary battery). Except for this, the evaluation cell (a lithium deposition-type all-solid-state lithium secondary battery) of this example was produced by 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) of this comparative example was produced in the same manner as in 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 3 μm.

[0081] Comparative Example 2 Except for not performing the rolling process using a roll press when preparing the carbon particle layer, an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) of this comparative example was prepared in the same manner as in the above-described comparative example 1. The thickness of the obtained carbon particle layer was 7 μm.

[0082] The carbon particles constituting the carbon particle layer are: graphite Except for using carbon black (intensity ratio R = 0.9) instead of the carbon black, 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-mentioned 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 a particle" refers to the direction of the line segment that indicates the maximum distance between two parallel lines when the outline of a carbon particle in an 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. On the other hand, 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 of the carbon particle layer was fixed to a stand 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 the 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 negative electrode current collector of the evaluation cell prepared above, respectively, and charging and discharging were 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) Charge / discharge conditions [Voltage range] 3.0~4.3V [Charging process] CCCV (0.01C cutoff) [Discharge process]CC [Charge / Discharge Rate] 0.1C or 3.5C (After charging and discharging, rest for 30 minutes each time) 2) Evaluation temperature: 333K (60℃).

[0087] The evaluation cells were charged in a constant current / constant voltage (CCCV) mode in a thermostatic chamber set to the evaluation temperature. The charging process (to deposit lithium metal on the negative electrode current collector) was performed in CCCV mode at the above-mentioned rate from 3.0 V to 4.3 V (0.01 C cutoff). The discharging process (to dissolve lithium metal on the negative electrode current collector) was then performed in 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 charging characteristics. The results are shown in Table 1 below. After the charge / discharge test, the evaluation cells were visually inspected for the location of lithium metal deposition. The results are also shown in Table 1 below.

[0088] [Table 1]

[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 charge-discharge ratio (V) 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. [Explanation of symbols]

[0092] 10a stacked 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 layers (carbon particle layers), 19 cell layer, 20 insulating layer, 21 power generation elements, 22 carbon black layer (ion-conductive reaction suppression layer), 23 Magnesium layer (lithium deposition energy reduction layer) 25 negative electrode current collector plate (negative electrode tab), 27 Positive current collector plate (positive tab), 29 Laminating film.

Claims

1. 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 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 ) is 7 or more.

2. 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.

3. The lithium secondary battery according to claim 1 or 2, wherein the carbon particles contain graphene.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. The lithium secondary battery according to claim 9 , wherein the ion-conductive reaction suppression layer has electronic conductivity.

11. The lithium secondary battery according to claim 9 , wherein the ion-conductive reaction suppression layer has electronic insulation properties.

12. 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.

13. 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.

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