Lithium-ion rechargeable battery

Abstract

The present invention provides a means to reduce the likelihood of internal short circuits occurring in lithium deposition type lithium secondary batteries. [Solution] A lithium secondary battery comprising a power generation element having 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 from 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, and a negative electrode intermediate layer interposed between the solid electrolyte layer and the negative electrode current collector and containing a lithium-reactive material selected from the group consisting of a carbon material capable of adsorbing lithium during charging and a metallic material capable of alloying with lithium, wherein at least a part of the outer peripheral edge of the negative electrode intermediate layer is provided with a low porosity portion having a smaller porosity than the central portion of the negative electrode intermediate layer.

Description

[Technical Field]

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

[0002] In recent years, research and development on lithium-ion secondary batteries using oxide-based or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of ion conduction in a solid state. Generally, using high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials can significantly improve the power density and energy density of the battery.

[0003] As one type of lithium secondary battery using a solid electrolyte, for example, Patent Document 1 proposes a technique in which a negative electrode active material layer (negative electrode intermediate layer) made of a metal-carbon composite is placed between the solid electrolyte layer and the negative electrode current collector. According to Patent Document 1, this configuration can prevent the aggregation phenomenon of metal particles and make the current distribution within the negative electrode layer uniform. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-98487 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, our investigations have revealed that in the lithium secondary batteries described in the above-mentioned literature, it may not be possible to prevent internal short circuits from occurring.

[0006] Therefore, the present invention aims to provide a means for making internal short circuits less likely to occur in lithium deposition type lithium secondary batteries. [Means for solving the problem]

[0007] The inventors of the present invention conducted diligent research to solve the above problems. As a result, they found that the above problems can be solved by providing a low porosity portion with a smaller porosity than the central portion at the outer edge of the negative electrode intermediate layer containing a lithium-reactive material in a lithium deposition type lithium secondary battery, and thus completed the present invention.

[0008] In other words, one embodiment of the present invention relates to a lithium secondary battery comprising a power generation element having 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 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, and a negative electrode intermediate layer interposed between the solid electrolyte layer and the negative electrode current collector and containing a lithium-reactive material selected from the group consisting of a carbon material capable of adsorbing lithium during charging and a metallic material capable of alloying with lithium. The lithium secondary battery is characterized in that at least a part of the outer peripheral edge of the negative electrode intermediate layer is provided with a low porosity portion, which has a smaller porosity than the central portion of the negative electrode intermediate layer. [Effects of the Invention]

[0009] According to the present invention, it is possible to make it less likely for internal short circuits to occur in a lithium deposition type lithium secondary battery. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) lithium secondary battery (stacked secondary battery), which is one embodiment of the present invention. [Figure 2] Figure 2 is an enlarged cross-sectional view of the single cell layers constituting the stacked secondary battery of the embodiment shown in Figure 1. [Modes for carrying out the invention]

[0011] One embodiment of the present invention is a lithium secondary battery comprising a power generation element having 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 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, and a negative electrode intermediate layer interposed between the solid electrolyte layer and the negative electrode current collector and containing a lithium-reactive material selected from the group consisting of a carbon material capable of adsorbing lithium during charging and a metallic material capable of alloying with lithium, wherein at least a part of the outer edge of the negative electrode intermediate layer is provided with a low porosity portion having a smaller porosity than the central portion of the negative electrode intermediate layer. The lithium secondary battery according to this embodiment has the effect of being less prone to generating internal resistance.

[0012] Embodiments of the present invention will be described below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0013] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery") which is one embodiment of the present invention. Figure 1 shows a cross-section of the stacked secondary battery during charging. The stacked secondary battery 10a shown in Figure 1 has a structure in which a substantially rectangular power generation element 21, in which the charge and discharge reaction actually proceeds, is sealed inside a laminate film 29 which is the battery casing. Here, the power generation element 21 has a structure in which a negative electrode, a 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 arranged so as to be in contact with the negative electrode active material layer 13 and the solid electrolyte layer 17, respectively. In this embodiment, a low porosity portion 14a is provided around the entire circumference of the outer edge of the negative electrode intermediate layer 14. This low-porosity portion 14a is a region with a smaller porosity than the central portion 14b of the negative electrode intermediate layer 14. The low-porosity portion 14a and the central portion 14b that constitute the negative electrode intermediate layer 14 contain a lithium-reactive material consisting of a carbon material (acetylene black) capable of absorbing lithium during charging and a metallic material (silver nanoparticles) capable of alloying with lithium, and further contain a binder (polyvinylidene fluoride (PVDF)).

[0014] The positive electrode has a structure in which a positive electrode active material layer 15 is arranged on the surface of the positive electrode current collector 11''. As a result, the negative electrode current collector 11'', the negative electrode active material layer 13, the negative electrode intermediate layer 14, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11'' constitute a single cell layer 19. Therefore, the stacked secondary battery 10a shown in Figure 1 can also be said to have a configuration in which multiple single cell layers 19 are stacked and electrically connected in parallel. The negative electrode current collector 11' and the positive electrode current collector 11'' are each fitted with a negative electrode current collector plate 25 and a positive electrode current collector plate 27, which are electrically connected to the respective electrodes (negative and positive electrodes), and have a structure that allows them to be led out of the laminate film 29 by being sandwiched between the edges of the laminate film 29. In the stacked secondary battery 10a, a restraining pressure is applied in the stacking direction of the power generation elements 21 by a pressurizing member (not shown). Therefore, the volume of the power generation elements 21 is kept constant.

[0015] Figure 2 is an enlarged cross-sectional view of a single cell layer constituting the laminated secondary battery of the embodiment shown in Figure 1. As shown in Figure 2, the single cell layer 19 constituting the laminated 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 its surface. Further, on the surface of the positive electrode active material layer 15 opposite to the positive electrode current collector 11", a solid electrolyte layer 17 containing a solid electrolyte is disposed. Here, in the embodiment shown in Figure 2, the outer peripheral edge portion of the solid electrolyte layer 17 extends to the side surface of the positive electrode active material layer 15 over its entire circumference. As a result, the positive electrode active material layer 15 is configured to be slightly smaller than the solid electrolyte layer 17. By adopting such a configuration, even if the lithium metal constituting the negative electrode active material layer 13 is extruded from the outer peripheral end of the solid electrolyte layer 17 toward the positive electrode active material layer 15 by the restraining pressure of the pressing member, it is difficult for the lithium metal to contact the side surface of the positive electrode active material layer 15. As a result, the effect of preventing short circuit becomes even higher. Note that the "side surface of the positive electrode active material layer" means the surface of the positive electrode active material layer that does not contact the positive electrode current collector and does not face the negative electrode current collector. Note that the outer peripheral edge portion of the solid electrolyte layer 17 does not necessarily have to extend to the side surface of the positive electrode active material layer 15.

[0016] Also, in the embodiment shown in Figure 2, a negative electrode intermediate layer 14 is disposed on the surface of the solid electrolyte layer 17 opposite to the positive electrode active material layer 15. In this negative electrode intermediate layer 14, as described with reference to Figure 1, a low porosity portion 14a is provided over the entire circumference of its outer peripheral edge portion, and the porosity of this low porosity portion 14a is smaller than the porosity of the central portion 14b. By providing such a low porosity portion 14a, the precipitation of lithium metal from the side surface of the negative electrode intermediate layer 14 is effectively prevented, and as a result, the short circuit of the battery is less likely to occur.

[0017] Hereinafter, the main constituent members of the lithium secondary battery according to this embodiment will be described.

[0018] <​​​​The current collectors (negative electrode current collector, positive electrode current collector) have the function of mediating the movement of electrons from the electrode active material layers (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the materials that make up the current collectors. For example, metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, or conductive resins can be used as constituent materials for the current collectors. There are also no particular restrictions on the thickness of the current collectors, but one example is 10 to 100 μm.

[0019] [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 made of lithium metal deposited during this charging process is the negative electrode active material layer of the lithium secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during complete discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be present during complete discharge. Furthermore, there are no particular restrictions on the thickness of the negative electrode active material layer (lithium metal layer) during complete charge, but it is usually 0.1 to 1000 μm.

[0020] [Negative electrode intermediate layer] The negative electrode intermediate layer is a layer interposed between the negative electrode current collector and the solid electrolyte layer, and contains a lithium-reactive material selected from the group consisting of carbon materials capable of adsorbing lithium during charging and metallic materials capable of alloying with lithium. By containing such a lithium-reactive material, the negative electrode intermediate layer exhibits the function of allowing lithium metal to be deposited more uniformly on the negative electrode (for example, on the negative electrode current collector).

[0021] The volume resistivity of the negative electrode intermediate layer is not particularly limited, but is preferably 10. 2 The resistivity is Ω·cm or less, and more preferably 10Ω·cm or less. In this specification, the volume resistivity of the negative electrode intermediate layer is the value measured using an electrode resistance measurement system (HIOKI E.E. CORPORATION, product name: RM2610).

[0022] Lithium-reactive materials can be carbon materials capable of absorbing lithium during charging. Specific examples of such carbon materials include carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal black, thermal lamp black, etc.), graphitized carbon black (derived from these), carbon nanotubes (CNTs), graphite, and hard carbon. Among these, carbon black is preferred, more preferably at least one selected from the group consisting of acetylene black, Ketjenblack®, furnace black, channel black, thermal black, and thermal lamp black, and particularly preferably acetylene black.

[0023] When the carbon material described above is in the form of particles, its average particle diameter (average primary particle diameter) is, for example, 10 nm to 200 nm, preferably 15 nm to 150 nm, more preferably 20 nm to 100 nm, and even more preferably 20 nm to 70 μm. In this specification, the average particle diameter of the carbon material is the 50% cumulative diameter (D) of the particle diameter of the particles observed in several to tens of fields of view when a cross-section of the layer containing the particles is observed with a scanning electron microscope (SEM) (the maximum distance between any two points on the contour line of the observed particles). 50 ) refers to.

[0024] Furthermore, the lithium-reactive material may include, in addition to or instead of, the carbon material described above, a metallic material that can alloy with lithium during charging. Examples of metallic materials that can alloy with lithium include In, Al, Si, Sn, Mg, Au, Ag, and Zn. Among these, In, Si, Sn, and Ag are preferred, and Ag is more preferred. The low-porosity portion and the central portion may each contain only one of the above-mentioned carbon material or metallic material. However, it is preferable that the low-porosity portion and the central portion each contain both the above-mentioned carbon material and the above-mentioned metallic material.

[0025] In a preferred embodiment, the lithium-reactive material is a combination of the carbon material described above and a metal that can alloy with lithium. That is, according to a preferred embodiment of the present invention, the lithium-reactive material includes a carbon material capable of intercalating lithium during charging and a metal material capable of alloying with lithium during charging. This ensures sufficient mechanical strength and lithium ion conductivity of the negative electrode intermediate layer. Furthermore, it can further suppress the occurrence of short circuits.

[0026] When the above metal material is in the form of particles, its average particle diameter is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and particularly preferably 100 nm or less. The lower limit of the average particle diameter of the metal particles is not particularly limited, but is preferably 20 nm or more. In this specification, the average particle diameter of the metal particles is the 50% cumulative diameter (D) of the particle diameter of the particles observed in several to tens of fields of view when a cross-section of the layer containing the particles is observed with a scanning electron microscope (SEM) (the maximum distance between any two points on the contour line of the observed particles). 50 ) refers to.

[0027] The negative electrode intermediate layer may consist solely of lithium-reactive material if a self-supporting film can be fabricated using only lithium-reactive material, but may also contain a binder as needed. Here, only the low-porosity portion and the central portion may contain a binder, but it is preferable that both contain a binder. The type of binder is not particularly limited, and any known in the art can be used as appropriate. Examples include fluororesins such as polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements) and polytetrafluoroethylene (PTFE), as well as styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC). Among these, the binder of the negative electrode intermediate layer preferably contains a fluororesin, and more preferably contains PVDF. It is even more preferable that it consists solely of VDF.

[0028] When the negative electrode intermediate layer contains a binder, the binder content is preferably more than 10 parts by mass, and more preferably 15 parts by mass or more, relative to 100 parts by mass of the total of the carbon material, lithium, and alloyable metal. When the binder content is within the above range, the strength of the negative electrode intermediate layer is sufficiently ensured, and cracks can be suppressed. There is no particular upper limit to the binder content, but from the viewpoint of suppressing resistance increase, it is preferably 35 parts by mass or less, relative to 100 parts by mass of the total of the carbon material, lithium, and alloyable metal.

[0029] The ratio of the total mass of the carbon material, the metal material, and the binder to the total mass of the negative electrode intermediate layer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass.

[0030] As described above, the lithium secondary battery according to this embodiment is characterized in that at least a portion of the outer edge of the negative electrode intermediate layer is provided with a low porosity portion, which has a smaller porosity than the central portion of the negative electrode intermediate layer. Here, the "porosity" of the low porosity portion and the central portion of the negative electrode intermediate layer is a value calculated from the low porosity portion and the central portion of the negative electrode intermediate layer in the discharged state after the lithium secondary battery has been completely discharged, the cell constraints have been released, and the outer casing has been removed, and this value was calculated using the "3D-SEM" described in the Examples section below.

[0031] The low porosity portion is a region with a lower porosity than the central portion of the negative electrode intermediate layer, and it is sufficient if it is provided in at least a part of the outer edge of the negative electrode intermediate layer. In the embodiments shown in Figures 1 and 2, the low porosity portion 14a is provided around the entire circumference of the outer edge of the negative electrode intermediate layer 14. This makes it more difficult for the battery to short-circuit.

[0032] The porosity value of the low-porosity section is not particularly limited as long as it is smaller than the porosity of the central section, but is preferably 40% or less, more preferably 30% or less, more preferably 25% or less, even more preferably 20% or less, and particularly preferably 15% or less. If the porosity value of the low-porosity section is within these ranges, the effect of making it less likely for the battery to short-circuit will be higher. In addition, the porosity value of the low-porosity section may be, for example, 29% or less, 28% or less, 27% or less, 26% or less, 25% or less, 24% or less, 23% or less, 22% or less, 21% or less, 20% or less, 19% or less, 18% or less, 17% or less, 16% or less, or 15% or less.

[0033] Furthermore, there are no particular restrictions on the value of the void ratio in the central part, as long as it is greater than the void ratio in the low-void ratio part, but for example, it should be greater than 40%, preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more. If the value of the void ratio in the central part is within these ranges, the effect of making it less likely for the battery to short-circuit will be greater. In addition, the value of the void ratio in the central part may be, for example, 51% or more, 52% or more, 53% or more, 54% or more, 55% or more, 56% or more, 57% or more, 58% or more, 59% or more, or 60% or more.

[0034] As described above, there are no particular limitations on the means of achieving low-porosity regions and central regions with different porosities, and various methods can be employed. One example is to use different types and compositions of materials that make up the low-porosity regions and central regions. Regarding the composition of the carbon material, metal material, and binder that make up the low-porosity regions and central regions, the porosity of those regions tends to increase as the proportion of carbon material and binder increases. Also, the porosity of those regions tends to decrease as the proportion of metal material increases. Furthermore, if the carbon material is amorphous carbon such as acetylene black, the DBP absorption value of the carbon material is Using smaller particles tends to reduce the porosity of that area. "DBP absorption" is the value expressed as the amount of DBP (dibutyl phthalate) absorbed per 100g of carbon black (mL / 100g), and is considered an indicator of the degree of development of the structure (connection between particles) of the carbon material. In this specification, the value of "DBP absorption" shall be the value calculated according to JIS K 6217-4:2017 "Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption (including compressed samples)". Furthermore, when two or more materials are used as carbon materials, the weighted average value obtained by weighting the DBP absorption of each material by its mass ratio shall be used as the DBP absorption of the carbon material. To change the DBP absorption value of the carbon material, the manufacturing conditions during production of the carbon material should be changed; details can be found in the common technical knowledge in this field. The DBP absorption value can also be changed by using two or more materials with different DBP absorption values ​​and adjusting the blending ratio of each material. In a preferred embodiment, the DBP absorption of the carbon material in the low-porosity portion is less than 200 [mL / 100g], and the DBP absorption of the carbon material in the central portion is 200 [mL / 100g] or more. In a more preferred embodiment, the DBP absorption of the carbon material in the low-porosity portion is 180 [mL / 100g] or less, and the DBP absorption of the carbon material in the central portion is 220 [mL / 100g] or more. The inventors also attempted to change the porosity by varying the pressing conditions (pressure and time) between the low-porosity portion and the central portion of the negative electrode intermediate layer. However, they confirmed that this method does not allow the porosity to be varied to the desired extent between the low-porosity portion and the central portion.

[0035] Furthermore, in a preferred embodiment, the content ratio (by mass) of the lithium-reactive material in the low porosity portion is greater than the content ratio (by mass) of the lithium-reactive material in the central portion. This configuration provides a greater effect in reducing the likelihood of short circuits in the battery. Here, the content ratio of the lithium-reactive material in the low porosity portion is preferably more than 75% by mass, more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more, based on 100% by mass of the total amount of material constituting the low porosity portion. On the other hand, the content ratio of the lithium-reactive material in the central portion is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 65% ​​by mass or less, based on 100% by mass of the total amount of material constituting the central portion. In the low-porosity region and the central region, if the lithium-reactive material includes both a carbon material capable of absorbing lithium during charging and a metal material capable of alloying with lithium during charging, the mixing ratio (mass ratio) of these materials is not particularly limited. However, in the central region, the carbon material:metal material (mass ratio) is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1. Within this range, battery performance is superior. In the low-porosity region, the carbon material:metal material (mass ratio) is preferably 1:1 to 1:5, and more preferably 1:2 to 1:3. Within this range, the porosity of the low-porosity region can be reliably kept small. In this case, the mass of the carbon material is the total mass of multiple types of carbon materials. Furthermore, if multiple types of metals capable of alloying with lithium are included, the mass is the total amount of the multiple types of metals capable of alloying with lithium.

[0036] In the embodiment shown in Figure 2, the thickness of the low porosity portion 14a is smaller than the thickness of the central portion 14b. This results in higher adhesion between the negative electrode intermediate layer 14 and the solid electrolyte layer 17 in the central portion 14b. As a result, the deposition of lithium metal via the lithium-reactive material present in the central portion 14b proceeds more easily, and the occurrence of short circuits at the edges is more effectively prevented. Here, the thickness of the central portion is not particularly limited, but is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, and particularly preferably 6 μm or less.

[0037] Furthermore, the thickness of the low porosity portion is not particularly limited, but is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 7 μm or less, and most preferably 5 μm or less. Moreover, the difference between the thickness of the low porosity portion and the thickness of the central portion is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, most preferably 4 μm or more, and most preferably 5 μm or more. The lower limit of the thickness of the negative electrode intermediate layer is not particularly limited, but from the viewpoint of ensuring the strength of the negative electrode intermediate layer, it is preferably 1.5 μm or more, more preferably 2 μm or more, and more preferably 4 μm or more.

[0038] Furthermore, in the embodiment shown in Figure 2, when the power generation element 21 is viewed from above (i.e., when the single cell layer 19 is viewed from above), each layer is arranged such that the outer edge of the solid electrolyte layer 17 is located outside the outer edge of the negative electrode intermediate layer 14 (i.e., the outer edge of the low porosity portion 14a) along its entire circumference. This ensures that the restraining pressure in the stacking direction applied by the pressurizing member is reliably applied to the outer edge of the negative electrode intermediate layer 14 (the outer edge of the low porosity portion 14a). As a result, the occurrence of short circuits at the ends is more effectively prevented. The above effect can be achieved if at least a portion of the outer edge of the solid electrolyte layer 17 is located outside the outer edge of the negative electrode intermediate layer 14 (the outer edge of the low porosity portion 14a), but as shown in Figure 2, it is preferable for the outer edge of the solid electrolyte layer 17 to be located outside the outer edge of the negative electrode intermediate layer 14 along its entire circumference, as this is more effective.

[0039] Furthermore, in the embodiment shown in Figure 2, when the power generation element 21 is viewed from above (i.e., when the single cell layer 19 is viewed from above), each layer is arranged such that the inner edge of the low porosity portion 14a coincides with the outer edge of the positive electrode active material layer 15 over its entire circumference. However, when the power generation element 21 is viewed from above, at least a portion of the inner edge of the low porosity portion 14a may be located outside the outer edge of the positive electrode active material layer 15. With this configuration, the deposition of lithium metal on the low porosity portion 14a located at the outer edge of the negative electrode intermediate layer 14 is suppressed. As a result, the occurrence of short circuits at the ends is more effectively prevented. The above effect is achieved if at least a portion of the inner edge of the low porosity portion 14a is located outside the outer edge of the positive electrode active material layer 15, but it is preferable for the inner edge of the low porosity portion 14a to be located outside the outer edge of the positive electrode active material layer 15 over its entire circumference, as this is more effective.

[0040] The method for manufacturing the negative electrode intermediate layer in the lithium secondary battery according to this embodiment is not particularly limited. For example, the negative electrode intermediate layer constituting the lithium secondary battery according to this embodiment can be manufactured by separately manufacturing a component that constitutes the central part of the negative electrode intermediate layer (for example, a square or rectangular shape) and a component that constitutes the low porosity part of the negative electrode intermediate layer (for example, a frame shape), and combining these. In this case, each part can be manufactured by preparing a slurry according to the composition of each part, and then coating and drying the slurry. Alternatively, the negative electrode intermediate layer constituting the lithium secondary battery according to this embodiment can also be manufactured by sequentially coating and drying the same slurry on the surface of a substrate (for example, a negative electrode current collector).

[0041] [Solid electrolyte layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as the main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any known in the art can be used as appropriate. Examples include LPS (Li2S-P2S5), Li6PS5X (where X is Cl, Br, or I), and Li7P3S 11 Li3.2 P 0.96 Examples of sulfide solid electrolytes include s and Li3PS4. These sulfide solid electrolytes are preferred because they have excellent lithium-ion conductivity and a low bulk modulus, allowing them to follow the volume changes of the electrode active material during charging and discharging. These solid electrolytes may be used individually or in combination of two or more. Of course, other solid electrolytes may also be used.

[0042] The ionic conductivity of a solid electrolyte at room temperature (25°C) (for example, the Li ion conductivity) is, for example, 1 × 10⁻⁶. -5 Preferably, S / cm or higher, 1 × 10 -4 A value of S / cm or higher is more preferable. The ionic conductivity of the solid electrolyte can be measured by the AC impedance method.

[0043] Examples of solid electrolyte shapes include spherical, ellipsoidal, and other particulate forms, as well as thin films. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 0.01 μm to 40 μm, more preferably 0.1 μm to 20 μm, and even more preferably 0.5 μm to 10 μm.

[0044] The solid electrolyte content in the solid electrolyte layer is preferably 50% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99% by mass.

[0045] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder that can be used in the solid electrolyte layer is the same as that described for the negative electrode intermediate layer.

[0046] The thickness of the solid electrolyte layer varies depending on the configuration of the intended all-solid-state lithium secondary battery, but is usually between 0.1 μm and 1000 μm, and preferably between 10 μm and 40 μm.

[0047] [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 / or a conductive assistant as required. The positive electrode active material layer is typically arranged on the surface of the positive electrode current collector as shown in FIG. 1. However, when the positive electrode active material layer 15 itself has a certain conductivity, it is also possible to form the positive electrode with the positive electrode active material layer itself without using the positive electrode current collector.

[0048] The type of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but a lithium-containing metal oxide is preferable. That is, according to a preferred embodiment of the present invention, the positive electrode active material contains at least one selected from lithium-containing metal oxides. According to a more preferred embodiment of the present invention, the positive electrode active material is composed of only at least one selected from lithium-containing metal oxides. Specific examples of the lithium-containing metal oxide include layered rock salt type active materials such as LiCoO2, LiMnO2, LiNiO2, Li(Ni-Mn-Co)O2, spinel type active materials such as LiMn2O4, LiNi 0.5 Mn 1.5 O4, olivine type active materials such as LiFePO4, LiMnPO4, Si-containing active materials such as Li2FeSiO4, Li2MnSiO4, etc. Further, examples of the oxide active material other than the above include, for example, Li4Ti5O 12 , LiVO2. Among them, Li(Ni-Mn-Co)O2 and those in which a part of these transition metals is substituted by other elements (NMC composite oxide) are preferably used as the positive electrode active material. These positive electrode active materials may be used alone or in combination of two or more.

[0049] In addition, it is also one of the preferred embodiments that a sulfur-based positive electrode active material is used. Examples of the sulfur-based positive electrode active material include particles or thin films of an organic sulfur compound or an inorganic sulfur compound, and any material that can utilize the oxidation-reduction reaction of sulfur to release lithium ions during charging and occlude lithium ions during discharging may be used.

[0050] The shape of the positive electrode active material can be, for example, particulate (spherical, fibrous), thin film, etc. If the positive electrode active material is in particulate form, its average particle diameter (D 50 ) is preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm. More preferably, the particle size is 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 (D) of the positive electrode active material is used. 50 The value of ) can be measured by laser diffraction scattering.

[0051] The content of the positive electrode active material is not particularly limited, but from the viewpoint of energy density, it is preferably, for example, 50% to 99% by mass, 70% to 99% by mass, more preferably 80% to 99% by mass, even more preferably 83% to 97% by mass, and particularly preferably 83% to 95% by mass, relative to the total mass of the positive electrode active material layer.

[0052] The positive electrode active material layer may further contain a solid electrolyte, a binder, and / or a conductive additive in addition to the positive electrode active material. Here, the solid electrolyte that can be used in the positive electrode active material layer is the same as that described for the solid electrolyte layer. The binder that can be used in the positive electrode active material layer is the same as that described for the negative electrode intermediate layer. Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNTs), and carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.). Furthermore, particulate ceramic materials or resin materials coated with the above metal materials by plating or the like can also be used as conductive additives.

[0053] The thickness of the positive electrode active material layer varies depending on the configuration of the intended all-solid-state lithium secondary battery, but is, for example, 0.1 μm to 1000 μm, preferably 30 μm to 300 μm, more preferably 50 μm to 200 μm, and even more preferably 70 μm to 150 μm.

[0054] [Positive electrode current collector plate and negative electrode current collector plate] The materials constituting the current collector plates (25, 27) are not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Preferred materials for the current collector plates are metallic materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. From the viewpoint of lightness, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0055] [Positive lead and negative lead] Furthermore, although not shown in the diagram, the current collectors (11”, 11') and the current collector plates (27, 25) may be electrically connected via positive and negative leads. The materials used for the positive and negative leads can be the same as those used in known lithium-ion batteries. It is preferable to cover the parts exposed from the casing with heat-resistant, heat-shrinkable tubing or the like to prevent leakage current from contacting peripheral equipment or wiring and affecting the product (e.g., automotive parts, especially electronic equipment).

[0056] [Battery casing material] As the battery casing material, known metal can cases can be used, or, as shown in Figure 1, a bag-shaped case made of an aluminum-containing laminate film 29 that can cover the power generation element can be used. For example, a three-layer laminate film made by laminating PP, aluminum, and nylon in that order can be used, but there is no limit to these. It offers high output and excellent cooling performance, and is suitable for EVs and HEVs. From the viewpoint of being suitable for use in batteries for large-scale equipment, laminate film is preferable. Furthermore, since the group pressure applied to the power generation elements from the outside can be easily adjusted, laminate film containing aluminum is more preferable as the outer material.

[0057] The all-solid-state lithium secondary battery according to this embodiment has a configuration in which multiple single cell layers are connected in parallel, resulting in high capacity and excellent cycle durability. Therefore, the all-solid-state lithium secondary battery according to this embodiment is suitable for use as a power source for EVs and HEVs.

[0058] 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-mentioned embodiment, and can be modified as appropriate based on the description of the claims.

[0059] For example, one type of battery to which the lithium secondary battery according to the present invention is applied is a bipolar battery that includes a bipolar electrode having a positive electrode active material layer electrically coupled to one side of a current collector and a negative electrode active material layer electrically coupled to the opposite side of the current collector.

[0060] Furthermore, the lithium secondary battery according to this embodiment does not have to be all-solid type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There are no particular restrictions on the amount of liquid electrolyte (electrolyte) 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 (electrolyte) does not occur.

[0061] Furthermore, the following items are also included within the scope of the present invention: Item 1: A positive electrode having a positive electrode active material layer containing a positive electrode active material, The negative electrode has a current collector, and lithium metal is deposited during charging. A solid electrolyte layer containing a solid electrolyte is interposed between the positive electrode and the negative electrode, A negative electrode intermediate layer is interposed between the solid electrolyte layer and the negative electrode current collector and contains a lithium-reactive material selected from the group consisting of a carbon material capable of absorbing lithium during charging and a metallic material capable of alloying with lithium, Equipped with a power generation element having, A lithium secondary battery in which at least a portion of the outer edge of the negative electrode intermediate layer is provided with a low porosity portion that has a smaller porosity than the central portion of the negative electrode intermediate layer; Item 2: The lithium secondary battery according to Item 1, wherein the low porosity portion is provided around the entire circumference of the outer edge of the negative electrode intermediate layer; Item 3: A lithium secondary battery according to item 1 or 2, wherein the lithium reactive material comprises carbon black (preferably acetylene black) as the carbon material; Item 4: A lithium secondary battery according to any one of items 1 to 3, wherein the lithium reactive material comprises In, Si, Sn, or Ag (preferably Ag) as the metallic material; Item 5: A lithium secondary battery according to any one of items 1 to 4, wherein the content ratio of the lithium-reactive material in the low porosity portion is greater than the content ratio of the lithium-reactive material in the central portion; Item 6: A lithium secondary battery according to any one of items 1 to 5, wherein both the low porosity portion and the central portion include a binder; Item 7: The lithium secondary battery according to Item 6, wherein the binder comprises a fluororesin (preferably PVDF); Item 8: A lithium secondary battery according to any one of items 1 to 7, wherein the sum of the masses of the carbon material, the metal material, and the binder, relative to the total mass of the negative electrode intermediate layer, is 90% by mass or more (preferably 100% by mass); Item 9: A lithium secondary battery according to any one of items 1 to 8, wherein the porosity in the low porosity portion is 30% or less (preferably 20% or less, more preferably 15% or less); Item 10: A lithium secondary battery according to any one of items 1 to 9, wherein the void ratio in the central portion is 50% or more (preferably 55% or more, more preferably 60% or more); Item 11: A lithium secondary battery according to any one of items 1 to 10, wherein in the low porosity portion and the central portion, the lithium reactive material contains the carbon material, the DBP absorption amount of the carbon material contained in the low porosity portion is less than 200 [mL / 100g], and the DBP absorption amount of the carbon material contained in the central portion is 200 [mL / 100g] or more; Item 12: The lithium secondary battery according to Item 11, wherein the DBP absorption amount of the carbon material contained in the low porosity portion is 180 [mL / 100g] or less, and the DBP absorption amount of the carbon material contained in the central portion is 220 [mL / 100g] or more; Item 13: A lithium secondary battery according to any one of items 1 to 12, wherein the content of the lithium-reactive material in the low porosity portion is more than 75% by mass (preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more) relative to 100% by mass of the total amount of material constituting the low porosity portion, and the content of the lithium-reactive material in the central portion is preferably 75% by mass or less (preferably 70% by mass or less, more preferably 65% ​​by mass or less) relative to 100% by mass of the total amount of material constituting the central portion; Item 14: A lithium secondary battery according to any one of items 1 to 13, wherein in the low porosity portion and the central portion, the lithium reactive material comprises both the carbon material and the metal material; Item 15: The lithium secondary battery according to Item 14, wherein in the central portion, the carbon material:metal material (mass ratio) is 10:1 to 1:1 (preferably 5:1 to 2:1); Item 16: A lithium secondary battery according to item 14 or 15, wherein in the low porosity portion, the carbon material:metal material (mass ratio) is 1:1 to 1:5 (preferably 1:2 to 1:3); Item 17: A lithium secondary battery according to any one of items 1 to 16, wherein, when the power generation element is viewed in plan, at least a portion of the outer peripheral edge of the solid electrolyte layer is located outside the outer peripheral edge of the negative electrode intermediate layer; Item 18: The lithium secondary battery according to item 17, wherein the outer peripheral edge of the solid electrolyte layer is located outside the outer peripheral edge of the negative electrode intermediate layer over its entire circumference; Item 19: A lithium secondary battery according to any one of items 1 to 18, wherein, when the power generation element is viewed from above, at least a portion of the inner circumferential edge of the low porosity portion is located outside the outer circumferential edge of the positive electrode active material layer; Item 20: The lithium secondary battery according to item 19, wherein the inner circumferential end of the low porosity portion is located outside the outer circumferential end of the positive electrode active material layer over its entire circumference; Item 21: A lithium secondary battery according to any one of items 1 to 20, wherein the thickness of the low porosity portion is less than the thickness of the central portion; Item 22: The lithium secondary battery according to Item 21, wherein the difference between the thickness of the low porosity portion and the thickness of the central portion is 1 μm or more (preferably 2 μm or more, more preferably 3 μm or more, even more preferably 4 μm or more, and particularly preferably 5 μm or more). [Examples]

[0062] 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 a dew point of -68°C or lower. Furthermore, the instruments and equipment used in the glove box were thoroughly dried beforehand.

[0063] <Example of creating evaluation cells> [Example 1] (Fabrication of the positive electrode) NMC composite oxide (LiNi) as positive electrode active material 0.8 Mn 0.1 Co 0.1 O2), carbon fiber as a conductive additive, and argyrodite-type sulfide solid electrolyte (Li6PS5Cl) as a solid electrolyte were weighed in a mass ratio of 85:15:5. After mixing using a mortar and pestle, the mixture was further stirred and mixed using a planetary ball mill. To 100 parts by mass of the resulting mixed powder, 2 parts by mass of polytetrafluoroethylene (PTFE) as a binder were added and mixed. The resulting mixture was layered with aluminum foil as a positive electrode current collector and subjected to a pressing process to obtain a positive electrode having a positive electrode active material layer (100 μm thick, outer dimensions 23 mm × 23 mm) on the surface of the positive electrode current collector.

[0064] (Preparation of a solid electrolyte layer) Algyrodite-type sulfide solid electrolyte as a solid electrolyte (Li6PS5Cl, average particle size (D 50 A solid electrolyte slurry was prepared by adding 2 parts by mass of styrene-butadiene rubber (SBR) as a binder to 100 parts by mass of (0.8 μm) material, and then adding and mixing with mesitylene as a solvent. A solid electrolyte layer (40 μm thick, 25 mm x 25 mm outer dimensions) was obtained by coating the solid electrolyte slurry onto the surface of a polyethylene terephthalate (PET) sheet used as a support and drying it.

[0065] (Fabrication of the negative electrode intermediate layer) Silver nanoparticles (average primary particle size: 60 nm), a metallic material that can alloy with lithium during charging, and acetylene black (average primary particle size: 200 nm, DBP absorption 175 mL / 100 g), a carbon material capable of absorbing lithium during charging, were weighed (Ag:C = 60:30 (mass ratio)) and mixed. To 90 parts by mass of the resulting mixture, 10 parts by mass of polyvinylidene fluoride (PVDF) as a binder was added, and N-methyl-2-pyrrolidone (NMP) was added as a solvent and mixed to prepare a negative electrode intermediate layer slurry (1) (for forming a low porosity region). On the other hand, silver nanoparticles (average primary particle size: 60 nm) and acetylene black (average primary particle size: 200 nm, DBP absorption 228 mL / 100 g) were weighed (Ag:C = 25:50 (mass ratio)) and mixed. To 75 parts by mass of the obtained mixture, 25 parts by mass of polyvinylidene fluoride (PVDF) as a binder was added, and N-methyl-2-pyrrolidone (NMP) was added as a solvent and mixed to prepare a negative electrode intermediate layer slurry (2) (for forming the central part).

[0066] Subsequently, the negative electrode intermediate layer slurry (2) obtained above was coated in a square shape onto the surface of the stainless steel foil used as the negative electrode current collector and dried to create the central part of the negative electrode intermediate layer (a 20 mm x 20 mm square). Furthermore, the negative electrode intermediate layer slurry (1) obtained above was coated in a 1.5 mm width around the outer circumference of the central part and dried to create the low porosity section of the negative electrode intermediate layer (a frame-shaped section with outer dimensions of 23 mm x 23 mm and inner dimensions of 20 mm x 20 mm). At this time, the size of the negative electrode intermediate layer was adjusted so that, when the power generation element is viewed in plan, the outer edge of the solid electrolyte layer is located outside the outer edge of the low porosity section that constitutes the negative electrode intermediate layer along its entire circumference, and the inner edge of the low porosity section is located outside the outer edge of the positive electrode active material layer along its entire circumference. In addition, the amount of each negative electrode intermediate layer slurry coated was adjusted so that the thickness of the low porosity section of the negative electrode intermediate layer was smaller than the thickness of the central part.

[0067] (Creation of evaluation cells) A positive electrode active material layer formed on the surface of an aluminum foil (positive electrode current collector) and a solid electrolyte layer formed on the surface of a PET sheet were placed on top of each other so that the exposed surfaces of the positive electrode active material layer and the exposed surfaces of the solid electrolyte layer faced each other, and pressed at 700 MPa for 1 minute using a cold isostatic press (CIP). This transferred the solid electrolyte layer to the exposed surface of the positive electrode active material layer. After peeling off the PET sheet adjacent to the solid electrolyte layer, the solid electrolyte layer and the negative electrode intermediate layer formed on the surface of a stainless steel foil (negative electrode current collector) were placed on top of each other so that the exposed surfaces of the solid electrolyte layer and the exposed surfaces of the negative electrode intermediate layer faced each other, and pressed at 500 MPa for 1 minute using a cold isostatic press (CIP). This transferred the negative electrode intermediate layer to the exposed surface of the solid electrolyte layer. Finally, an aluminum positive electrode tab and a nickel negative electrode tab were joined to the aluminum foil (positive electrode current collector) and stainless steel foil (negative electrode current collector), respectively, using an ultrasonic welding machine, and the resulting laminate was aluminum laminated. An evaluation cell for this embodiment, which is a lithium deposition type lithium secondary battery, was fabricated by placing it inside a film and vacuum sealing it.

[0068] [Example 2] An evaluation cell for this example was prepared using the same method as in Example 1 described above, except that the mass ratio of silver nanoparticles:acetylene black:PVDF contained in the negative electrode intermediate layer slurry (1) for forming the low porosity region was changed from 60:30:10 to 50:25:25.

[0069] [Comparative Example 1] The evaluation cell for this comparative example was prepared using the same method as in Example 1 described above, except that the acetylene black contained in the negative electrode intermediate layer slurry (1) for forming the low porosity region was changed to acetylene black (average primary particle size: 200 nm, DBP absorption amount 228 mL / 100 g), and the mass ratio of silver nanoparticles:acetylene black:PVDF contained in the negative electrode intermediate layer slurry (1) for forming the low porosity region was changed from 60:30:10 to 25:50:25.

[0070] [Comparative Example 2] An evaluation cell for this comparative example was prepared using the same method as in Comparative Example 1 described above, except that the mass ratio of silver nanoparticles:acetylene black:PVDF contained in the negative electrode intermediate layer slurry (1) for forming the low porosity region was changed from 25:50:25 to 20:70:10.

[0071] [Comparative Example 3] The evaluation cell for this comparative example was prepared using the same method as in Example 1 described above, except that the acetylene black contained in the negative electrode intermediate layer slurry (2) for central region formation was changed to acetylene black (average primary particle size: 200 nm, DBP absorption amount: 175 mL / 100 g), and the mass ratio of silver nanoparticles:acetylene black:PVDF contained in the negative electrode intermediate layer slurry (2) for central region formation was changed from 25:50:25 to 60:30:10.

[0072] <Measurement of the thickness of the negative electrode intermediate layer> For each of the evaluation cells prepared in the above-described examples and comparative examples, the thickness of the low-porosity portion and the central portion constituting the negative electrode intermediate layer was measured. Here, the thickness of the negative electrode intermediate layer was calculated from the negative electrode intermediate layer in the discharged state after the cell constraints were released and the outer casing was removed following the complete discharge of the lithium secondary battery. Specifically, the power generation element was removed from the evaluation cell after complete discharge, and a cross section perpendicular to the surface direction (laminated cross section) was exposed by ion milling. The above cross section was then observed by SEM, and the thickness was measured at several to several dozen different locations in both the low-porosity portion and the central portion of the negative electrode intermediate layer, and the arithmetic mean of these measurements was taken as the thickness of the negative electrode intermediate layer. As a result, for all evaluation cells, the thickness of the low-porosity portion was 7 μm, and the thickness of the central portion was 10 μm. Note that, in this study, the thickness of the negative electrode intermediate layer was measured after complete discharge for the evaluation cells after the charge-discharge test described later, but similar values ​​for the thickness of the negative electrode intermediate layer were obtained for the evaluation cells before the initial charge.

[0073] <Measurement of porosity in the negative electrode intermediate layer> For each of the evaluation cells prepared in the above-described examples and comparative examples, the porosity of the low-porosity portion and the central portion constituting the negative electrode intermediate layer was measured using the following method.

[0074] First, the power generation elements were removed from the lithium secondary battery after complete discharge, and the cross-sections perpendicular to the surface direction (stacked cross-sections) were exposed in the low porosity region and the central region, respectively, by ion milling. Next, Hitachi High-Tech Science Co., Ltd. focused ion beam processing - Using a Focused Ion Beam Scanning Electron Microscope (FIB-SEM), SEM images (5 μm × 5 μm size) were taken of the front view of the stacked cross-section of the power generation element, specifically of the surface portions of the low-porosity region and the central region. Subsequently, the surfaces of the low-porosity region and the central region were irradiated with an ion beam to excavate them, and images of the surfaces were taken again. The excavation and imaging of the surfaces by ion beam irradiation were repeated to obtain a set of 2D images of the surface. Then, each 2D region of the obtained set of 2D images was identified, the area of ​​voids in that 2D region was calculated, the volume of voids in the 3D region was calculated by integrating this area, and the porosity was calculated by calculating the volume of voids relative to the total volume of the 3D region. Note that during the calculation of porosity, the lithium metal present in the negative electrode intermediate layer was considered as voids in the measurement. Here, lithium metal was identified using high-sensitivity EDS, and its area was calculated based on the contrast of the identified lithium metal. The porosity values ​​of the low-porosity and central regions measured in this way are shown in Table 1 below.

[0075] <Charge / Discharge Test> The evaluation cells (before initial charging) prepared as described above were subjected to charging and discharging according to the following charge / discharge test conditions. During this process, a constraining pressure of 3 MPa was applied to the stacking direction of the evaluation cells using a pressurizing member while performing the following charge / discharge tests.

[0076] (Charge / discharge test conditions) Evaluation temperature: 333K (60℃) Voltage range: 2.5~4.3V Charging process: CCCV (cutoff at 0.1mA) Charging rate: 0.01C Discharge process:CC Discharge rate: 0.5C After charging and discharging, let it rest for 30 minutes.

[0077] The evaluation cells were subjected to charge-discharge testing using a charge-discharge tester in a constant temperature chamber set to the evaluation temperature described above. During the charging process (deposition of lithium metal on the negative electrode current collector), the constant current-constant voltage (CCCV) mode was used. The cells were charged to 4.3V with a constant current of 0.01C, and then charged at a constant voltage until the current dropped to 0.1mA. Subsequently, during the discharge process (dissolution of lithium metal on the negative electrode current collector), the constant current (CC) mode was used, and the cells were discharged to 2.5V at 0.5C. Here, 1C is the current value at which the battery is fully charged (100% charged) after charging for one hour. The above charge-discharge was considered the first charge-discharge cycle. A 200-cycle charge-discharge test was performed on 240 evaluation cells for each experimental example and comparative example. The percentage of cells that short-circuited during the 200 charge-discharge cycles was calculated as the short-circuit rate [%]. The results are shown in Table 1 below.

[0078] [Table 1]

[0079] The results shown in Table 1 indicate that lithium deposition type lithium secondary batteries, such as the evaluation cells in Examples 1 and 2, which have a low porosity region at the outer edge of the negative electrode intermediate layer, are less prone to internal short circuits. [Explanation of Symbols]

[0080] 10A stacked secondary battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 14. Negative electrode intermediate layer, 14a Low porosity part, 14b central part, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layers, 21 Power generation elements, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29. Laminating film.

Claims

1. A positive electrode having a positive electrode active material layer containing positive electrode active material, The negative electrode has a current collector, and lithium metal is deposited during charging. A solid electrolyte layer containing a solid electrolyte is interposed between the positive electrode and the negative electrode, A negative electrode intermediate layer is interposed between the solid electrolyte layer and the negative electrode current collector and contains a lithium-reactive material selected from the group consisting of a carbon material capable of absorbing lithium during charging and a metallic material capable of alloying with lithium, Equipped with a power generation element having, A lithium secondary battery wherein at least a portion of the outer peripheral edge of the negative electrode intermediate layer is provided with a low porosity portion that has a smaller porosity than the central portion of the negative electrode intermediate layer.

2. The lithium secondary battery according to claim 1, wherein the content ratio of the lithium-reactive material in the low porosity portion is greater than the content ratio of the lithium-reactive material in the central portion.

3. The lithium secondary battery according to claim 1 or 2, wherein the porosity in the low porosity portion is 30% or less.

4. The lithium secondary battery according to claim 1 or 2, wherein the void ratio in the central portion is 50% or more.

5. The lithium secondary battery according to claim 1 or 2, wherein, when the power generation element is viewed in plan, at least a portion of the outer peripheral edge of the solid electrolyte layer is located outside the outer peripheral edge of the negative electrode intermediate layer.

6. The lithium secondary battery according to claim 1 or 2, wherein, when the power generation element is viewed in plan, at least a portion of the inner circumferential end of the low porosity portion is located outside the outer circumferential end of the positive electrode active material layer.

7. The lithium secondary battery according to claim 1 or 2, wherein the thickness of the low porosity portion is smaller than the thickness of the central portion.

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