Lithium secondary battery

Abstract

To provide a means capable of suppressing short circuit in a lithium deposition type lithium secondary battery.SOLUTION: A power generation element including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging, a first solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and a negative electrode intermediate layer disposed between the solid electrolyte layer and the negative electrode current collector so as to be adjacent thereto, the negative electrode intermediate layer includes a central portion disposed at a position facing the positive electrode active material layer, and an outer peripheral portion disposed on at least a part of an outer periphery of the central portion so as to be separated from the first solid electrolyte layer and electrically connected to the central portion via the current collector, and a reaction potential of the outer peripheral portion is higher than a reaction potential of the central portion.SELECTED DRAWING: Figure 1

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 pinning its hopes on reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and there has been active development of secondary batteries, such as those 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 secondary batteries used in mobile phones, laptops, etc. Therefore, lithium 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 secondary batteries use flammable organic electrolytes, and these liquid-based lithium 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 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. Therefore, lithium secondary batteries that use solid electrolytes do not, in principle, encounter the various problems associated with flammable organic electrolytes that occur in conventional liquid-based lithium 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 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 (see, for example, Patent Document 1). During charging of such lithium deposition type lithium secondary batteries, lithium metal is deposited between a solid electrolyte layer and a negative electrode current collector. Patent Document 1 discloses a technique in which a fine particle layer (negative electrode intermediate layer) containing fine particles such as amorphous carbon (e.g., carbon black) is disposed between the negative electrode current collector and the solid electrolyte layer, which constitute the power generating element of the lithium secondary battery. According to Patent Document 1, with this configuration, when lithium metal is deposited between the fine particle layer and the negative electrode current collector during charging, the fine particle layer acts as a protective layer for the lithium metal layer and suppresses the growth of dendrites from the lithium metal layer, thereby preventing short circuits in the lithium secondary battery and the resulting decrease in capacity. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2012 / 060349 Summary of the Invention [Problem to be solved by the invention]

[0008] However, according to the study by the present inventors, it has been found that even if the technique described in Patent Document 1 is used, there are cases where it is not possible to prevent a short circuit when the charging rate is increased.

[0009] Therefore, an object of the present invention is to provide a means for improving the charge rate of a lithium deposition type secondary battery without causing a short circuit. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by providing a region with a high reaction potential on the outer periphery of a negative electrode intermediate layer disposed between a negative electrode current collector and a solid electrolyte layer, thereby completing 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 having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging, a first solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and a negative electrode intermediate layer disposed adjacent to the solid electrolyte layer and the negative electrode current collector. In the lithium secondary battery, the negative electrode intermediate layer includes a central portion disposed opposite the positive electrode active material layer, and an outer peripheral portion disposed on at least a part of the outer periphery of the central portion, spaced from the first solid electrolyte layer and electrically connected to the central portion via the current collector, and the reaction potential of the outer peripheral portion is higher than the reaction potential of the central portion. [Effects of the Invention]

[0012] According to the present invention, it is possible to improve the charge rate at which a short circuit does not occur in a lithium deposition type secondary battery. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view that schematically illustrates the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention. [Figure 2] 2 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to one embodiment of the present invention. FIG. [Figure 3] FIG. 4 is an enlarged cross-sectional view of a unit cell layer of a stacked secondary battery according to another embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing a modification of the embodiment shown in FIG. [Figure 5]FIG. 10 is an enlarged cross-sectional view of a unit cell layer of a stacked secondary battery according to still another embodiment of the present invention. [Figure 6] FIG. 10 is an enlarged cross-sectional view of a unit cell layer of a stacked secondary battery according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A lithium secondary battery according to one embodiment of the present invention includes a power generating element including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging, a first solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and a negative electrode intermediate layer disposed adjacent to the solid electrolyte layer and the negative electrode current collector. In the lithium secondary battery, the negative electrode intermediate layer includes a central portion facing the positive electrode active material layer, and an outer peripheral portion disposed on at least a portion of the outer periphery of the central portion, spaced apart from the first solid electrolyte layer and electrically connected to the central portion via the current collector, wherein the reaction potential of the outer peripheral portion is higher than the reaction potential of the central portion.

[0015] Hereinafter, a secondary battery according to the present embodiment will be described with reference to the accompanying drawings. The technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. In the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted. In addition, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0016] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. FIG. 1 shows a cross section of the stacked-type secondary battery during charging. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior. The power generating element 21 has a structure in which a negative electrode, a first solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11′ and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11′ are stacked. A negative electrode intermediate layer 14 is disposed adjacent to the surface of the negative electrode active material layer 13 facing the first solid electrolyte layer 17. The positive electrode has a structure in which a positive electrode active material layer 15 is disposed on the surface of a positive electrode current collector 11". The negative electrode, first solid electrolyte layer 17, and positive electrode are laminated in this order, with the negative electrode intermediate layer 14 and the positive electrode active material layer 15 facing each other with the first solid electrolyte layer 17 interposed therebetween. As a result, adjacent negative electrodes, first solid electrolyte layers 17, and positive electrodes constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a structure in which a plurality of unit cell layers 19 are laminated and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27, which are electrically connected to the respective electrodes (negative electrode and positive electrode), are attached to the negative electrode current collector 11' and the positive electrode current collector 11", respectively, and are structured to be sandwiched between the ends of the laminate film 29 and led out of the laminate film 29. A pressure member (not shown) applies a restraining pressure to the stacked secondary battery 10a in the stacking direction of the power generating element 21. Therefore, the volume of the power generating element 21 is kept constant.

[0017] FIG. 2 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to one embodiment of the present invention. As shown in FIG. 2, a cell layer 19 constituting a stacked secondary battery 10a 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 first 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. 2, a negative electrode intermediate layer central portion 14a is provided on the main surface of the first solid electrolyte layer 17 facing the negative electrode current collector 11′. A material having lithium ion conductivity is selected as the material constituting this negative electrode intermediate layer central portion 14a, and the negative electrode intermediate layer central portion 14a can conduct lithium ions. Therefore, the provision of the negative electrode intermediate layer central portion 14a does not impede the progress of the battery reaction. Furthermore, this negative electrode intermediate layer central portion 14a also has the function of suppressing a reaction between the lithium metal (negative electrode active material layer 13) deposited on the negative electrode current collector 11′ during charging and the solid electrolyte contained in the first solid electrolyte layer 17. Therefore, it can be said that this negative electrode intermediate layer central portion 14a functions as an ion-conductive reaction suppression layer.

[0018] 2, in the cell layer 19 constituting the stacked secondary battery 10a according to this embodiment, a negative electrode intermediate layer peripheral portion 14b is provided around the entire periphery of the negative electrode intermediate layer central portion 14a. The material constituting this peripheral portion 14b is also a material that has lithium ion conductivity. Therefore, lithium ions can permeate from the negative electrode intermediate layer central portion 14a to the peripheral portion 14b.

[0019] In the embodiment shown in FIG. 2, when the power generating element 21 is viewed from above, the outer peripheral edges of the positive electrode active material layer 15 and the first solid electrolyte layer 17 coincide with the outer peripheral edge of the central portion 14a. Furthermore, these outer peripheral edges are all positioned inside the outer peripheral edge of the outer peripheral portion 14b along the entire periphery and coincide with the inner peripheral edge of the outer peripheral portion 14b. In FIG. 2(a), the thickness of the outer peripheral portion 14b in the stacking direction is smaller than the thickness of the central portion 14a in the stacking direction. In FIG. 2(b), the thickness of the outer peripheral portion 14b in the stacking direction is the same as the thickness of the central portion 14a in the stacking direction. In both the configurations shown in FIGS. 2(a) and 2(b), the first solid electrolyte layer 17 and the outer peripheral portion 14b are spaced apart from each other. This configuration prevents lithium ions from diffusing directly from the first solid electrolyte layer 17 to the outer peripheral portion 14b during charging. As a result, lithium ions are uniformly distributed between the central portion 14a and the peripheral portion 14b, which has the advantage of suppressing the growth of lithium dendrites in the central portion 14a and more effectively preventing short circuits due to contact between the dendrites and the first solid electrolyte layer 17 and / or the positive electrode active material layer 15.

[0020] Fig. 3 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to another embodiment of the present invention, and Fig. 4 is a diagram showing a modification of the embodiment shown in Fig. 3.

[0021] In the embodiment shown in FIG. 3, when the power generating element 21 is viewed from above, the outer peripheral edge of the first solid electrolyte layer 17 is located inside the outer peripheral edge of the central portion 14a. Specifically, in FIG. 3(a), the outer peripheral edge of the central portion 14a coincides with the outer peripheral edge of the positive electrode active material layer 15. However, as shown in FIG. 3(b), the outer peripheral edge of the central portion 14a may be located inside the outer peripheral edge of the positive electrode active material layer 15. Furthermore, as shown in FIG. 4, the outer peripheral edge of the positive electrode active material layer 15 may be located inside the outer peripheral edge of the central portion 14a. In the case of the shape shown in FIGS. 3 and 4, even if the thickness of the outer peripheral portion 14b is increased, the outer peripheral portion 14b does not come into contact with the first solid electrolyte layer 17 (and further the positive electrode active material layer 15), which has the advantage of allowing the volume of the outer peripheral portion 14b to be increased and more lithium ions to be absorbed.

[0022] FIG. 5 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to yet another embodiment of the present invention. In the embodiment shown in FIG. 5, the outer peripheral edge of the central portion 14a is located inside the outer peripheral edge of the first solid electrolyte layer 17. This structure prevents lithium dendrites from growing from the negative electrode side along the side surface of the first solid electrolyte layer 17 to reach the positive electrode side, a phenomenon known as wraparound growth. Furthermore, in order to prevent contact between the outer peripheral portion 14b and the first solid electrolyte layer 17, the ratio of the thickness of the outer peripheral portion 14b in the stacking direction to the thickness of the central portion 14a in the stacking direction (thickness of the central portion 14a / thickness of the outer peripheral portion 14b) needs to be less than 1.0.

[0023] Fig. 6 is an enlarged cross-sectional view of a cell layer of a stacked secondary battery according to still another embodiment of the present invention. In the embodiment shown in Fig. 6, a second solid electrolyte layer 17' containing a solid electrolyte is provided between the outer peripheral portion 14b and the central portion 14a. This shape has the advantage of more reliably preventing the so-called wraparound growth described above.

[0024] 2 to 6, each layer has a rectangular parallelepiped shape (i.e., a rectangular shape in cross section), but is not limited thereto. For example, in the cross section in the stacking direction of FIG. 2, the outer peripheral portion 14b may have a trapezoid shape with the long side facing the negative electrode current collector.

[0025] The main components of the lithium secondary battery according to this embodiment will be described below.

[0026] [Current collector] The current collectors (negative electrode current collector, positive electrode current collector) function to mediate the transfer of electrons from the electrode active material layers (negative electrode active material layer, positive electrode active material layer). There are no particular limitations on the material that constitutes the current collectors. Examples of materials that can be used for the current collectors include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular limitations on the thickness of the current collectors, but an example is 10 to 100 μm.

[0027] [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 during the charging process. The layer composed of the lithium metal deposited during the 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.

[0028] [Negative electrode intermediate layer] The negative electrode intermediate layer is a layer adjacent to the surface of the first solid electrolyte layer facing the negative electrode current collector. It includes a central portion (also referred to herein as the "negative electrode intermediate layer central portion" or simply "central portion") facing the positive electrode active material layer, and an outer peripheral portion (also referred to herein as the "negative electrode intermediate layer outer peripheral portion" or simply "outer peripheral portion") located at least partly around the periphery of the central portion, spaced apart from the first solid electrolyte layer and electrically connected to the central portion via the current collector. The negative electrode intermediate layer is preferably electrically conductive as a whole. In this specification, the volume resistivity of the negative electrode intermediate layer is measured using an electrode resistance measurement system (manufactured by Hioki E.E. Corporation, product name: RM2610).

[0029] (Center of negative electrode intermediate layer) The central portion may contain a carbon material. By containing a carbon material, the central portion can absorb lithium, which can contribute to suppressing the generation and growth of dendrites. The carbon material is not particularly limited, but examples include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, it is preferable to contain at least one of carbon black, graphite, and hard carbon, and graphite or hard carbon is more preferable. The use of such a carbon material further improves the performance of absorbing and desorbing lithium ions.

[0030] The content of the carbon material is, for example, 99% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less, relative to 100% by mass of the total amount of the central portion. There is no particular lower limit to the content of the carbon material, but it is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, relative to 100% by mass of the total amount of the central portion. When the content of the carbon material is within the above range, the generation and growth of dendrites can be suppressed.

[0031] The central portion may additionally contain a metal material. Examples of the metal material include, but are not limited to, indium (In), aluminum (Al), silicon (Si), tin (Sn), magnesium (Mg), gold (Au), silver (Ag), and zinc (Zn). When the central portion contains a metal material, lithium metal can be deposited more uniformly on the current collector surface. Among these, it is preferable to contain at least one of indium (In), silicon (Si), tin (Sn), and silver (Ag), and it is more preferable to contain silver (Ag). The content of the metal material is, but is not limited to, for example, 0 to 50% by mass, and preferably 20 to 45% by mass, of the total mass of the central portion.

[0032] When a carbon material and a metal material are used in combination in the central portion, the compounding ratio (mass ratio) of these is not particularly limited, but the carbon material:metal material ratio is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1.

[0033] The central portion may contain a binder, if necessary. The type of binder is not particularly limited, and any binder known in the art may be used as appropriate. Examples include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose. The central portion may not contain a binder, and may contain, for example, only a carbon material and a metal material.

[0034] The binder content in the central portion is not particularly limited, but is preferably in the range of 1 to 20% by mass, and more preferably in the range of 1 to 15% by mass, relative to 100% by mass of the total amount of the central portion. If the binder content is 1% by mass or more, a central portion with sufficient strength can be formed. If the binder content is 20% by mass or less, a decrease in energy density can be suppressed.

[0035] The central portion may be a porous body, for example, a porous body containing a carbon material and a metal material, or, for example, a porous body made only of a carbon material and a metal material. When the central portion has such a configuration, the central portion has even better lithium ion absorption and desorption capabilities.

[0036] The thickness of the central portion is not particularly limited, but is preferably in the range of 1 to 50 μm, more preferably in the range of 5 to 40 μm, and even more preferably in the range of 8 to 20 μm. When the thickness of the central portion is 1 μm or more, the function as a protective layer can be sufficiently exhibited. When the thickness of the central portion is 50 μm or less, a decrease in energy density can be suppressed.

[0037] (Outer periphery of negative electrode intermediate layer) The outer periphery may contain one or more selected from the group consisting of silicon, alloys, lithium-containing composite oxides, sulfur, transition metal oxides, and transition metal sulfides. For example, the outer periphery may contain silicon, alloys, lithium titanate (LiTiO), 12 ), sulfur, a transition metal oxide, and a transition metal sulfide. In one embodiment, the outer periphery may contain one or more selected from the group consisting of silicon, tin, an alloy, lithium titanate, sulfur, a transition metal oxide, and a transition metal sulfide. In one embodiment, the outer periphery contains one or more selected from the group consisting of silicon, tin, an alloy, and lithium titanate, for example, one or more selected from the group consisting of silicon and lithium titanate.

[0038] The alloy is not particularly limited as long as it is an alloy that can be alloyed with lithium, and examples thereof include Li-Ag alloys, Li-Sn alloys, Li-Si alloys, and Si multi-component alloys, etc. Examples of Si multi-component alloys include the multi-component alloys described in JP-A-2009-517850.

[0039] In addition to the lithium titanate, examples of lithium-containing composite oxides include lithium manganese oxide (LiMn2O4), lithium cobalt oxide (LiCoO2), lithium cobalt nickel manganese oxide (Li(Co,Ni,Mn)O2), and lithium nickel oxide (LiNiO2).

[0040] Examples of transition metal oxides include titanium oxide (TiO2), niobium oxide (Nb2O3), tungsten oxide (WO3), vanadium pentoxide (V2O5), and iron oxide (FeO X ), manganese dioxide (MnO2), etc.

[0041] Examples of transition metal sulfides include titanium sulfide (TiS2) and molybdenum sulfide (MoS2).

[0042] The outer periphery may further contain a binder as needed. The binder is not particularly limited, and known binders can be used as appropriate. For example, the binders described above for the central portion can be similarly used. The content of the binder in the outer periphery is not particularly limited, and is, for example, 0 to 20 mass %.

[0043] The thickness of the outer periphery is not particularly limited, but is preferably within the range of 0.5 to 200 μm, more preferably within the range of 5 to 40 μm, and even more preferably within the range of 10 to 30 μm.

[0044] The ratio of the thickness of the outer periphery in the stacking direction to the thickness of the central portion in the stacking direction (thickness of outer periphery / thickness of central portion) is not particularly limited as long as the first solid electrolyte layer and the outer periphery do not come into contact with each other, but may be, for example, 0.1 to 10, preferably 0.5 to 4.0. When the outer periphery edge of the first solid electrolyte layer and the outer periphery edge of the central portion are aligned in a planar view of the power generating element, the ratio of the thickness of the outer periphery in the stacking direction to the thickness of the central portion in the stacking direction may be 0.1 to 1.0, preferably 0.5 to 1.0, and more preferably 1.0. Since the amount of lithium ions occluded in the outer periphery increases as the volume of the outer periphery increases, the thickness of the outer periphery is preferably larger as long as it does not come into contact with the first solid electrolyte layer. When the outer periphery of the first solid electrolyte layer is located inside the outer periphery of the central portion in a planar view of the power generating element, the ratio of the thickness of the outer periphery in the stacking direction to the thickness of the central portion in the stacking direction may be 0.1 to 10, preferably greater than 1.0 but not greater than 10.

[0045] The ratio of the perimeter of the outer part to the perimeter of the center part (perimeter of the outer part / center part) The ratio of the length between the outer circumferential edge and the inner circumferential edge of the outer circumferential portion to the outer circumferential length of the central portion (length between the outer circumferential edge and the inner circumferential edge of the outer circumferential portion / outer circumferential length of the central portion) may be, for example, 0.5 / 80 to 1.5 / 80, or 0.8 / 80 to 1.2 / 80.

[0046] (reaction potential) As described above, one of the features of the lithium secondary battery according to this embodiment is that the reaction potential at the outer periphery is higher than the reaction potential at the center. In this specification, the "reaction potential" (unit: V vs. Li / Li + ) is the ratio of Li in the electrode made of the constituent materials based on the lithium ion deposition reaction. + The reaction potential can be measured by the method described in the Examples. The reaction potential in the central region is, for example, −0.5 to 0.5 [V vs. Li / Li +], and preferably −0.1 to 0.1 [V vs. Li / Li + The reaction potential of the outer periphery is not particularly limited as long as it is higher than the reaction potential of the central portion, and is, for example, 0.1 to 2.0 [V vs. Li / Li + ], and preferably 0.3 to 1.8 [V vs. Li / Li + ] can be.

[0047] Although the detailed mechanism by which the charge rate at which a short circuit occurs can be improved by the reaction potential of the peripheral portion of the negative electrode intermediate layer being higher than that of the central portion is unclear, the following reason is presumed. Note that the following mechanism is merely speculation, and the technical scope of the present invention is not limited thereby. In a lithium secondary battery according to one embodiment of the present invention, during charging, lithium metal deposition first progresses between the central portion of the negative electrode intermediate layer and the negative electrode current collector. Then, lithium absorption progresses in the central portion of the negative electrode intermediate layer, which is in direct contact with the first solid electrolyte. This phenomenon proceeds more preferentially than in the peripheral portion, which is spaced apart from the first solid electrolyte. Next, when lithium is saturated in the central portion, lithium ions migrate from the central portion to the peripheral portion due to the difference in reaction potential at the interface between the central portion and the peripheral portion. This absorption of lithium ions in the peripheral portion uniformly distributes lithium ions, suppressing localized lithium metal deposition and preventing the occurrence of short circuits due to the growth of lithium dendrites, even during charging at higher charge rates.

[0048] (Second solid electrolyte layer) A second solid electrolyte layer may be disposed between the outer periphery and the central portion. In this specification, the solid electrolyte layer disposed between the outer periphery and the central portion is referred to as the "second solid electrolyte layer," and the solid electrolyte layer disposed between the positive electrode active material layer (described later) and the central portion is referred to as the "first solid electrolyte layer." Therefore, the order of "first" and "second" has no meaning; these terms are merely used to distinguish the locations where the solid electrolyte layers are present. When a second solid electrolyte layer is disposed, the outer periphery and the central portion are disposed spaced apart from each other. The second solid electrolyte layer and the first solid electrolyte layer are also disposed spaced apart from each other. By disposing the second solid electrolyte layer, the conduction of lithium ions from the central portion to the outer periphery can be further promoted.

[0049] The second solid electrolyte layer usually contains a solid electrolyte as a main component. The solid electrolyte contained in the second solid electrolyte layer is not particularly limited, and any known solid electrolyte in the art can be appropriately adopted, including sulfide solid electrolytes and oxide solid electrolytes. From the viewpoint of high ionic conductivity, the solid electrolyte is preferably a sulfide solid electrolyte, more preferably a sulfide solid electrolyte containing Li, M, and S, where 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 S, Li, and P. Examples include LPS (Li2S-P2S5), Li6PS5X (where X is Cl, Br, or I), and Li7P3S 11 , Li 3.2 P 0.96 Examples of sulfide solid electrolytes include sulfide solid electrolytes such as S and Li3PS4. These sulfide solid electrolytes have excellent lithium ion conductivity and are therefore preferably used. The ion conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25°C) is, for example, 1 × 10 -5 S / cm or more is preferable, and 1×10 -4 It is more preferable that the ionic conductivity is S / cm or more. The ionic conductivity value of the solid electrolyte can be measured by an AC impedance method.

[0050] The content of the solid electrolyte in the second solid electrolyte layer is preferably 50 to 100 mass %, and more preferably 90 to 100 mass %.

[0051] The second solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder is not particularly limited, and known binders can be used as appropriate. For example, the binders described above for the negative electrode intermediate layer can be similarly used. The content of the binder in the second solid electrolyte layer is not particularly limited, and is, for example, 1 to 20 mass %.

[0052] [First solid electrolyte layer] The first solid electrolyte layer is a layer that typically contains a solid electrolyte as a main component and is interposed between the negative electrode active material layer and the positive electrode active material layer. The solid electrolyte contained in the first solid electrolyte layer is not particularly limited, and any known solid electrolyte may be used as appropriate. For example, the solid electrolyte described above for the second solid electrolyte layer may be similarly employed.

[0053] The content of the solid electrolyte in the first solid electrolyte layer is preferably 50 to 100 mass %, and more preferably 90 to 100 mass %.

[0054] The first solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder is not particularly limited, and known binders can be used as appropriate. For example, the binders described above for the negative electrode intermediate layer can be similarly employed. The content of the binder in the solid electrolyte layer is not particularly limited, and is, for example, 1 to 20 mass %.

[0055] The thickness of the first solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 100 μm.

[0056] The ratio of the outer periphery of the first solid electrolyte layer to the outer periphery of the central portion (outer periphery of first solid electrolyte layer / outer periphery of central portion) may be, for example, 0.5 or more and less than 1.0. In one embodiment, the ratio of the outer periphery of the first solid electrolyte layer to the outer periphery of the central portion may be 1.0 or more and 1.5 or less, or may be more than 1.0 and 1.3 or less.

[0057] [Cathode active material layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and a conductive additive as needed.

[0058] The type of positive electrode active material contained in the positive electrode active material layer is not particularly limited, but may be 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. 12 Among these, Li(Ni-Mn-Co)O2 and those in which part of the transition metals is replaced with other elements (hereinafter also simply referred to as "NMC composite oxides") are preferably used as the positive electrode active material.

[0059] In another 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 can release lithium ions during charging and absorb lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0060] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is, for example, preferably 30 to 99 mass %, more preferably 40 to 95 mass %, and even more preferably 45 to 90 mass %.

[0061] The positive electrode active material layer preferably further contains a solid electrolyte. Specific forms of the solid electrolyte contained in the positive electrode active material layer may be the same as those described in the section on the second solid electrolyte layer. A sulfide solid electrolyte is preferably used because it has excellent lithium ion conductivity and a low bulk modulus, allowing it to follow the volumetric changes of the positive electrode active material that accompany charge and discharge. The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but is, for example, 1 to 70 mass %, preferably 3 to 60 mass %, and more preferably 5 to 55 mass %.

[0062] The binder used in the positive electrode active material layer is not particularly limited, and known binders can be used as appropriate. For example, the binder described in the center section above can be used. The content of the binder in the positive electrode active material layer is not particularly limited, and is, for example, 1 to 10 mass%.

[0063] The conductive additive used in the positive electrode active material layer is not particularly limited, and may be, for example, carbon such as carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). The content of the conductive additive in the positive electrode active material layer is not particularly limited, and is, for example, 1 to 30 mass%.

[0064] The thickness of the positive electrode active material layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 300 μm.

[0065] The ratio of the outer periphery of the positive electrode active material layer to the outer periphery of the central portion (outer periphery of the positive electrode active material layer / outer periphery of the central portion) may be, for example, 0.5 or more and less than 1.0. In one embodiment, the ratio of the outer periphery of the positive electrode active material layer to the outer periphery of the central portion may be 1.0 or more and 1.5 or less, or may be more than 1.0 and 1.3 or less.

[0066] [Positive and negative current collector plates] The material constituting the current collector plate is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate and the negative electrode current collector plate may be made of the same material or different materials.

[0067] [Positive and negative leads] The current collector and the current collecting plate may be electrically connected via a positive electrode lead or a negative electrode lead. Materials used in known lithium secondary batteries may be used as the constituent materials of the positive electrode and negative electrode leads. It is preferable that the portion removed from the outer casing be covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting the product (e.g., automobile parts, particularly electronic devices).

[0068] Although one embodiment of the lithium secondary battery of the present invention has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0069] The following items are also included within the scope of the present invention: Item 1: A lithium secondary battery comprising a power generating element including: a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging; a first solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a negative electrode intermediate layer disposed between the solid electrolyte layer and the negative electrode current collector so as to be adjacent thereto, wherein the negative electrode intermediate layer includes a central portion disposed in a position facing the positive electrode active material layer, and an outer peripheral portion disposed on at least a part of the outer periphery of the central portion, spaced apart from the first solid electrolyte layer and electrically connected to the central portion via the current collector, and wherein the reaction potential of the outer peripheral portion is higher than the reaction potential of the central portion; Item 2: The lithium secondary battery according to Item 1, wherein the ratio of the thickness of the outer periphery in the stacking direction to the thickness of the central portion in the stacking direction is 0.1 to 1.0 (preferably 0.5 to 1.0, more preferably 1.0); Item 3: The lithium secondary battery according to Item 1, wherein the ratio of the thickness of the outer periphery in the stacking direction to the thickness of the central portion in the stacking direction is 0.1 to 10 (preferably 0.5 to 10, more preferably more than 1.0 and 4.0 or less); Item 4: The lithium secondary battery according to any one of Items 1 to 3, wherein, in a plan view of the power generating element, the outer peripheral edge of the first solid electrolyte layer is located inside the outer peripheral edge of the central portion; Item 5: The lithium secondary battery according to any one of Items 1 to 4, wherein, when the power generating element is viewed from above, the outer peripheral edge of the central portion coincides with or is located inside the outer peripheral edge of the positive electrode active material layer; Item 6: The lithium secondary battery according to any one of Items 1 to 5, wherein, when the power generating element is viewed from above, the outer circumferential edge of the positive electrode active material layer is located inside the outer circumferential edge of the central portion; Item 7: The lithium secondary battery according to Item 1, wherein, in a plan view of the power generating element, the outer peripheral edge of the central portion is located inside the outer peripheral edge of the first solid electrolyte layer, and the ratio of the thickness of the outer peripheral portion in the stacking direction to the thickness of the central portion in the stacking direction is less than 1.0 (preferably 0.1 or more and less than 1.0, more preferably 0.5 or more and less than 1.0, and even more preferably 0.7 or more and less than 1.0); Item 8: The lithium secondary battery according to any one of Items 1 to 7, wherein the outer periphery is spaced apart from the central portion, and a second solid electrolyte layer containing a solid electrolyte is disposed between the outer periphery and the central portion; Item 9: The lithium secondary battery according to any one of Items 1 to 8, wherein the central portion contains a carbon material (preferably at least one of acetylene black, graphite, and hard carbon), and the outer peripheral portion contains one or more selected from the group consisting of a metal (preferably tin or silicon), an alloy, a lithium-containing composite metal (preferably lithium titanate (LTO)), sulfur, a transition metal oxide, and a transition metal sulfide; Item 10: The lithium secondary battery according to Item 9, wherein the carbon material includes graphite or hard carbon; Item 11: The lithium secondary battery according to any one of Items 1 to 10, wherein the central portion is a porous body containing a carbon material and a metal material. [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, operations were carried out in a glove box with 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) First, LiNi as the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2, acetylene black as a conductive additive, and Li6PS5Cl as a solid electrolyte were weighed out in a mass ratio of 90:1:9. These were mixed in an agate mortar and then further stirred and mixed using a planetary ball mill. To 100 parts by mass of the resulting mixed powder, 2 parts by mass of styrene-butadiene rubber (SBR) as a binder and mesitylene as a solvent were added and mixed to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to the surface of an aluminum foil positive electrode current collector, dried, and pressed to obtain a positive electrode with a positive electrode active material layer (20 mm × 20 mm, 200 μm thick) on the surface of the positive electrode current collector.

[0072] (Preparation of a laminate of positive electrode current collector / positive electrode active material layer / first solid electrolyte layer) A solid electrolyte slurry was prepared by adding 2 parts by mass of SBR as a binder to 100 parts by mass of Li6PS5Cl as a solid electrolyte, and adding mesitylene as a solvent and mixing them. The solid electrolyte slurry was applied to the surface of a stainless steel foil support and dried to prepare a first solid electrolyte layer (20 mm × 20 mm, 50 μm thick; hereinafter also referred to as the "first SE layer"). Next, the positive electrode active material layer of the positive electrode prepared above and the first solid electrolyte layer prepared similarly above were overlapped so that they faced each other, and then bonded together by cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute). The stainless steel foil on the first solid electrolyte layer side was peeled off, yielding a laminate of a positive electrode current collector / positive electrode active material layer / first solid electrolyte layer.

[0073] (Preparation of slurry for the central part of the negative electrode intermediate layer) Graphite (average particle size (D50) = 20 μm) and silver nanoparticles (average primary particle size (D50): 60 nm) were weighed and mixed to a mass ratio of graphite (Gr):Ag = 3:1. 14 parts by mass of polyvinylidene fluoride (PVdF) was added to 86 parts by mass of the resulting mixture as a binder, and N-methyl-2-pyrrolidone was added as a solvent and mixed to prepare a slurry for the central portion of the negative electrode intermediate layer.

[0074] (Preparation of Slurry for Outer Portion of Negative Electrode Intermediate Layer) Lithium titanate (LTO) powder, acetylene black as a conductive additive, and Li6PS5Cl as a solid electrolyte were mixed in a mass ratio of 90:1:9, and N-methyl-2-pyrrolidone was added to this solid content as a solvent and mixed to prepare a slurry for the outer periphery of the negative electrode intermediate layer.

[0075] (Preparation of evaluation cells) The surface of a stainless steel foil serving as a negative electrode current collector was masked using masking tape to ensure that the negative electrode intermediate layer peripheral portion formed below was properly formed. The negative electrode intermediate layer peripheral portion slurry prepared above was then applied to the centrally masked stainless steel foil, dried, and then subjected to cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute). The stainless steel foil masking the negative electrode current collector was then peeled off, and a negative electrode intermediate layer peripheral portion (1 mm wide, 5 μm thick) was formed on the peripheral edge of the surface of the negative electrode current collector.

[0076] The surfaces of the negative electrode current collector and the outer peripheral portion of the negative electrode intermediate layer were then masked so that the central portion of the negative electrode intermediate layer formed below had an appropriate shape. Next, the central portion of the exposed surface of the negative electrode current collector on which the outer peripheral portion of the negative electrode intermediate layer was formed was coated with the slurry for the central portion of the negative electrode intermediate layer prepared above and dried. After that, the slurry was subjected to cold isostatic pressing (700 MPa, 25°C, 1 minute). The masking material was then peeled off, and the central portion of the negative electrode intermediate layer (20 mm × 20 mm, 10 μm thick) was formed in the central portion of the negative electrode current collector. Finally, the negative electrode current collector on which the negative electrode intermediate layer central portion and negative electrode intermediate layer peripheral portion obtained above were formed and a laminate of positive electrode current collector / positive electrode active material layer / first solid electrolyte layer were stacked so that the exposed surface of the negative electrode intermediate layer central portion faced the exposed surface of the first solid electrolyte layer, and cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute) was performed to produce an evaluation cell (lithium deposition-type all-solid-state lithium secondary battery) having the configuration shown in FIG. 2.

[0077] [Example 2] The evaluation cell of this example was produced in the same manner as in Example 1, except that in the above (production of evaluation cell), the thickness of the outer peripheral portion of the negative electrode intermediate layer was changed to 10 μm.

[0078] [Example 3] (Preparation of positive electrode) The positive electrode of this example was produced in the same manner as in Example 1.

[0079] (Preparation of a laminate of positive electrode current collector / positive electrode active material layer / first solid electrolyte layer) A laminate of the positive electrode current collector / positive electrode active material layer / first solid electrolyte layer of this example was obtained in the same manner as in Example 1, except that the dimensions of the first solid electrolyte layer were changed to 16 mm × 16 mm.

[0080] (Preparation of slurry for the central part of the negative electrode intermediate layer) In the same manner as in Example 1, a slurry for the central portion of the negative electrode intermediate layer of this example was prepared.

[0081] (Preparation of Slurry for Outer Portion of Negative Electrode Intermediate Layer) In the same manner as in Example 1, a slurry for the outer peripheral portion of the negative electrode intermediate layer of this example was prepared.

[0082] (Preparation of evaluation cells) This example differs from Example 1 in that the central part of the negative electrode intermediate layer is formed first, and the thickness of the peripheral part of the negative electrode intermediate layer is set to 20 μm.

[0083] Specifically, the surface of a stainless steel foil negative electrode current collector was first masked to ensure that the central portion of the negative electrode intermediate layer formed below was properly formed. The masked negative electrode current collector was then coated with the slurry for the central portion of the negative electrode intermediate layer prepared above, dried, and then subjected to cold isostatic pressing (700 MPa, 25°C, 1 minute). The masking material was then peeled off from the negative electrode current collector, and the central portion of the negative electrode intermediate layer (20 mm × 20 mm, 10 μm thick) was formed in the central portion of the surface of the negative electrode current collector.

[0084] The surfaces of the negative electrode current collector and the central part of the negative electrode intermediate layer were then masked so that the negative electrode intermediate layer peripheral part formed below had an appropriate shape. Next, the negative electrode intermediate layer peripheral part slurry prepared above was applied to the peripheral edge part of the exposed surface of the negative electrode current collector on which the negative electrode intermediate layer central part was formed above and dried, and then cold isostatic pressing treatment (700 MPa, 25°C, 1 minute) was performed. The masking material was then peeled off, and the negative electrode intermediate layer peripheral part (1 mm wide, 20 μm thick) was formed on the peripheral part of the negative electrode current collector. Finally, the negative electrode current collector on which the negative electrode intermediate layer central portion and negative electrode intermediate layer peripheral portion obtained above were formed and a laminate of positive electrode current collector / positive electrode active material layer / first solid electrolyte layer were stacked so that the exposed surface of the negative electrode intermediate layer central portion faced the exposed surface of the first solid electrolyte layer, and cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute) was performed to produce an evaluation cell for this example.

[0085] [Example 4] The evaluation cell of this example was produced in the same manner as in Example 3, except that in the above (preparation of positive electrode), the dimensions of the positive electrode active material layer were changed to 16 mm × 16 mm, and in the above (preparation of evaluation cell), the thickness of the outer periphery of the negative electrode intermediate layer was changed to 40 μm.

[0086] [Example 5] An evaluation cell for this example was fabricated in the same manner as in Example 1, except that in the above (Fabrication of the first solid electrolyte layer), the dimensions of the first solid electrolyte layer were changed to 24 mm x 24 mm.

[0087] [Example 6] The evaluation cell of this example was produced in the same manner as in Example 2, except that the operation of (production of evaluation cell) was carried out in the following manner.

[0088] (Preparation of evaluation cells) The operation of this example differs from that of Example 2 in that a second solid electrolyte layer is first provided between the central portion of the negative electrode intermediate layer and the outer peripheral portion of the negative electrode intermediate layer.

[0089] Specifically, the surface of a stainless steel foil negative electrode current collector was first masked to ensure that the negative electrode intermediate layer peripheral portion formed as described below was properly formed. The masked negative electrode current collector was then coated with the negative electrode intermediate layer peripheral portion slurry prepared above, dried, and then subjected to cold isostatic pressing (700 MPa, 25°C, 1 minute). The masking material was then peeled off, and the negative electrode intermediate layer peripheral portion (1 mm wide, 10 μm thick) was formed on the peripheral edge of the surface of the negative electrode current collector.

[0090] The surface of the negative electrode current collector was then masked so that the second solid electrolyte layer formed below would have an appropriate shape. Next, the solid electrolyte slurry prepared above was applied to the exposed surface of the negative electrode current collector on which the outer peripheral portion of the negative electrode intermediate layer had been formed above, dried, and then subjected to cold isostatic pressing (700 MPa, 25°C, 1 minute). The masking material was then peeled off, and a second solid electrolyte layer (1 mm wide, 10 μm thick; hereinafter also referred to as the "second SE layer") was formed inside the outer peripheral portion of the negative electrode intermediate layer.

[0091] Thereafter, the negative electrode intermediate layer central part slurry prepared above was applied to the central part of the exposed surface of the negative electrode current collector on which the second solid electrolyte layer was formed above, and after drying, cold isostatic pressing treatment (700 MPa, 25°C, 1 minute) was performed, and the masking material was peeled off, thereby forming a negative electrode intermediate layer central part (20 mm × 20 mm, thickness 10 μm) in the central part of the negative electrode current collector.

[0092] Finally, the negative electrode current collector on which the above-obtained negative electrode intermediate layer central portion, second solid electrolyte layer, and negative electrode intermediate layer peripheral portion were formed and a laminate of positive electrode current collector / positive electrode active material layer / first solid electrolyte layer were stacked so that the exposed surface of the negative electrode intermediate layer central portion faced the exposed surface of the first solid electrolyte layer, and the resultant was subjected to cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute) to produce an evaluation cell for this example.

[0093] [Example 7] The evaluation cell of this example was produced in the same manner as in Example 1, except that in the above (preparation of the material for the outer periphery of the negative electrode intermediate layer), silicon (Si) powder was used instead of lithium titanate (LTO) powder.

[0094] [Comparative Example 1] An evaluation cell for this comparative example was produced in the same manner as in Example 2, except that in the above (production of evaluation cell), the outer peripheral portion of the negative electrode intermediate layer was not formed.

[0095] Comparative Example 2 An evaluation cell for this comparative example was produced in the same manner as in Example 3, except that in the above (Production of a laminate of a positive electrode current collector / positive electrode active material layer / first solid electrolyte layer), the dimensions of the first solid electrolyte layer were changed to 20 mm × 20 mm, and in the above (Production of an evaluation cell), the thickness of the outer periphery of the negative electrode intermediate layer was changed to 15 μm.

[0096] <Measurement of reaction potential> (Production of LTO anode) The negative electrode intermediate layer outer peripheral part slurry obtained in Example 1 (Preparation of material for the negative electrode intermediate layer outer peripheral part) was applied to a stainless steel foil by a doctor blade method, and excess non-aqueous electrolyte was sucked through an aramid separator to obtain an LTO negative electrode in which a 100 μm-thick negative electrode active material layer was formed on the surface of the stainless steel foil serving as a negative electrode current collector.

[0097] (Fabrication of Si anode) The negative electrode intermediate layer outer peripheral part slurry obtained in Example 7 (Preparation of material for the negative electrode intermediate layer outer peripheral part) was applied to a stainless steel foil by a doctor blade method, and excess non-aqueous electrolyte was sucked through an aramid separator to obtain a Si negative electrode in which a 100 μm-thick negative electrode active material layer was formed on the surface of the stainless steel foil serving as a negative electrode current collector.

[0098] (Measurement of electrode potential) Each negative electrode prepared above was laminated with metallic lithium foil via a separator and sealed with an aluminum laminate film to prepare a test half cell. Charging was evaluated using this cell, and the average potential was calculated. The charging conditions were as follows: the current required to charge the theoretical capacity of each active material for one hour was 1 C, and charging was performed at 0.05 C. The voltage range for the LTO negative electrode was 1.0 V vs. Li / Li. + ], and for the Si anode, it is 0.03 [V vs. Li / Li + As a result, the LTO negative electrode had a voltage of 1.55 [V vs. Li / Li + ], and the Si negative electrode is 0.5 [V vs. Li / Li + ] was.

[0099] <Evaluation of the test cell (presence or absence of short circuits due to dendrites)> The positive and negative electrode leads were connected to the positive and negative current collectors of the test cell, respectively, and the test was performed in a thermostatic chamber at 25°C. The current required for one hour of charging when the capacity of the positive electrode active material was 220 mAh / g was defined as a 1C current. Constant-current charging was performed at several charge rates from 0% SOC to 80% SOC, and the test cell was examined for the presence or absence of short circuits. A voltage drop in the test cell during charging was considered to have occurred; no voltage drop was observed, indicating that a short circuit had not occurred. This test was performed at various current values, and the maximum current value (C) at which a short circuit did not occur was determined. The results are shown in Table 1 below.

[0100] In Table 1 below, "width" corresponds to the length of one side of each layer when the power generating element is viewed in a plane, and indicates the ratio of the length of one side of each layer (length of one side of each layer / length of one side of the central part) when the length of one side of the central part is set to 1.

[0101] [Table 1]

[0102] The results in Table 1 reveal that, in a lithium deposition-type secondary battery, providing a region with a high reaction potential on the outer periphery of the negative electrode intermediate layer disposed between the negative electrode current collector and the solid electrolyte layer can suppress the occurrence of short circuits even during charging at a higher charge rate than in the comparative example. Furthermore, when the interior of the evaluation cell was observed after charging at a current value of 1.3 C in Example 5, no growth of lithium dendrites was observed. This is thought to be due to the fact that the area of ​​the first solid electrolyte layer was larger than that of the middle layer of the negative electrode intermediate layer and the positive electrode layer, thereby increasing the distance that lithium dendrites travel from the center of the negative electrode intermediate layer to reach the positive electrode active material layer. [Explanation of symbols]

[0103] 10a stacked battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 14a: the center of the negative electrode intermediate layer; 14b: the outer periphery of the negative electrode intermediate layer; 15 positive electrode active material layer, 17 first solid electrolyte layer, 17' second solid electrolyte layer; 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film.

Claims

1. a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging; a first solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; a negative electrode intermediate layer disposed adjacent to and between the solid electrolyte layer and the negative electrode current collector; a power generating element having the negative electrode intermediate layer includes a central portion disposed at a position facing the positive electrode active material layer, and an outer peripheral portion disposed at at least a part of the outer periphery of the central portion, the outer peripheral portion being spaced apart from the first solid electrolyte layer and electrically connected to the central portion via the current collector; A lithium secondary battery, wherein the reaction potential of the outer periphery is higher than the reaction potential of the central portion.

2. 3. The lithium secondary battery according to claim 1, wherein a ratio of the thickness of said outer periphery in the stacking direction to the thickness of said central portion in the stacking direction is 0.5 to 1.

0.

3. 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 first solid electrolyte layer is located inside an outer peripheral edge of the central portion.

4. The lithium secondary battery according to claim 3 , wherein, when the power generating element is viewed from above, the outer circumferential edge of the central portion coincides with or is located inside the outer circumferential edge of the positive electrode active material layer.

5. The lithium secondary battery according to claim 3 , wherein, when the power generating element is viewed from above, the outer circumferential edge of the positive electrode active material layer is located inside the outer circumferential edge of the central portion.

6. When the power generating element is viewed from above, an outer peripheral edge of the central portion is located inside an outer peripheral edge of the first solid electrolyte layer, 3. The lithium secondary battery according to claim 1, wherein a ratio of the thickness of said outer peripheral portion in the stacking direction to the thickness of said central portion in the stacking direction is less than 1.

0.

7. 3. The lithium secondary battery according to claim 1, wherein the outer periphery is spaced apart from the central portion, and a second solid electrolyte layer containing a solid electrolyte is disposed between the outer periphery and the central portion.

8. the central portion comprises a carbon material; 3. The lithium secondary battery according to claim 1, wherein the outer periphery contains one or more selected from the group consisting of silicon, an alloy, lithium titanate (LTO), sulfur, a transition metal oxide, and a transition metal sulfide.

9. 9. The lithium secondary battery according to claim 8, wherein the carbon material comprises graphite or hard carbon.

10. 9. The lithium secondary battery according to claim 8, wherein the central portion is a porous body made of a carbon material and a metal material.

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