JP7659991B2 - Lithium secondary battery - Google Patents

Description

The present invention relates to a lithium secondary battery.

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

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

The currently widely used lithium-ion secondary batteries use a flammable organic electrolyte as the electrolyte. These liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, overcharging, etc. than other batteries.

In recent years, therefore, there has been active research and development into all-solid-state lithium secondary batteries that use oxide- or sulfide-based solid electrolytes. A solid electrolyte is a material that is primarily composed of ion conductors that are capable of ion conduction in a solid state. For this reason, in principle, all-solid-state lithium secondary batteries do not encounter the various problems caused by flammable organic electrolytes that occur in conventional liquid-based lithium-ion secondary batteries. In addition, the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials generally leads to a significant improvement in the output density and energy density of the battery.

Conventionally, as one type of all-solid-state lithium secondary battery, a so-called lithium precipitation type battery in which metallic lithium is precipitated on the negative electrode current collector during charging is known (see, for example, Patent Document 1). In the charging process of such a lithium precipitation type all-solid-state lithium secondary battery, metallic lithium is precipitated between the solid electrolyte layer and the negative electrode current collector. Therefore, a space is required between the solid electrolyte layer and the negative electrode current collector for metallic lithium to precipitate. If such a space does not exist sufficiently, there are problems such as the growth of dendrites due to the precipitation of metallic lithium causing an internal short circuit, and problems such as the overvoltage when metallic lithium is precipitated during the charging process becoming large and the charge/discharge rate characteristics deteriorating. Patent Document 1 attempts to prevent the occurrence of such problems by providing a lithium occlusion layer containing carbon and solid electrolyte and having a porosity of 60% or more between the solid electrolyte layer and the negative electrode current collector.

JP 2019-33053 A

However, the inventors' investigations have revealed that even if the technology described in Patent Document 1 is used, there are still cases where sufficient charge/discharge rate characteristics cannot be achieved.

The present invention aims to provide a means for improving the charge/discharge rate characteristics of lithium precipitation type lithium secondary batteries.

The present inventors have conducted extensive research to solve the above problems, and as a result, have found that in a secondary battery including a lithium deposition-type power generating element and a pressing member that presses the power generating element in the stacking direction, the above problems can be solved by controlling the ten-point average roughness (R _zJIS ) of the surface of the negative electrode current collector on the solid electrolyte layer side within a predetermined range, thereby completing the present invention.

That is, one aspect of the present invention relates to a lithium secondary battery including a positive electrode having a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions, a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging, a power generating element having a solid electrolyte layer interposed between the positive electrode and the negative electrode, and a pressing member that presses the power generating element with a predetermined pressure in a stacking direction, and the battery is characterized in that the ten-point average roughness (R _zJIS ) of the surface of the negative electrode current collector on the side of the solid electrolyte layer is 3 to 50 μm.

The present invention can improve the charge/discharge rate characteristics of lithium precipitation type lithium secondary batteries.

1 is a cross-sectional view showing a schematic overall structure of a stacked type (internal parallel connection type) all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a negative electrode current collector of the stacked secondary battery according to one embodiment of the present invention. 1 is a perspective view of a stacked secondary battery according to one embodiment of the present invention; FIG. 4 is a side view seen from a direction A shown in FIG. 3 . 1 is a perspective view showing the appearance of a stacked secondary battery according to one embodiment of the present invention;

One aspect of the present invention is a lithium secondary battery comprising: a positive electrode having a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions; a negative electrode having a negative electrode current collector, on which lithium metal is deposited during charging; a power generating element having a solid electrolyte layer interposed between the positive electrode and the negative electrode; and a pressure member that presses the power generating element with a predetermined pressure in a stacking direction, the surface of the negative electrode current collector on the side of the solid electrolyte layer having a ten-point average roughness (R _zJIS ) of 3 to 50 μm. The lithium secondary battery according to this aspect can improve the charge and discharge rate characteristics in a lithium deposition type lithium secondary battery.

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

Figure 1 is a cross-sectional view showing a schematic overall structure of a stacked type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked type secondary battery") according to one embodiment of the present invention. The stacked type secondary battery 10a shown in Figure 1 has a structure in which a roughly rectangular power generation element 21, where the actual charge/discharge reaction takes place, is sealed inside a laminate film 29, which is the battery exterior. Note that a restraining pressure is applied to the stacked type secondary battery 10a in the stacking direction of the power generation element 21 by a pressure member (not shown). Therefore, the volume of the power generation element 21 is kept constant.

As shown in FIG. 1, the power generating element 21 of the stacked secondary battery 10a of this embodiment has a structure in which a negative electrode in which a carbon layer 13 containing Ketjen Black (registered trademark) and a solid electrolyte is arranged on both sides of a negative electrode collector 11', a solid electrolyte layer 17, and a positive electrode in which a positive electrode active material layer 15 containing a lithium transition metal composite oxide is arranged on both sides of a positive electrode collector 11" are stacked. Specifically, the negative electrode, the solid electrolyte layer, and the positive electrode are stacked in this order so that one carbon layer 13 and the adjacent positive electrode active material layer 15 face each other through the solid electrolyte layer 17. As a result, the adjacent negative electrode, solid electrolyte layer, and positive electrode constitute one single 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 single cell layers 19 are stacked and electrically connected in parallel.

A negative electrode collector 25 and a positive electrode collector 27 that are electrically connected to the electrodes (negative and positive) are attached to the negative electrode collector 11' and the positive electrode collector 11", respectively, and are structured so as to be sandwiched between the ends of the laminate film 29 and led out of the laminate film 29. The negative electrode collector 25 and the positive electrode collector 27 may be attached to the negative electrode collector 11' and the positive electrode collector 11" of each electrode by ultrasonic welding, resistance welding, or the like, via negative electrode terminal leads and positive electrode terminal leads (not shown), respectively, as necessary.

In the above description, an embodiment of an all-solid-state battery according to one aspect of the present invention has been described using a stacked type (internal parallel connection type) all-solid-state lithium secondary battery as an example. However, the type of all-solid-state battery to which the present invention can be applied is not particularly limited, and the present invention can also be applied to bipolar type all-solid-state batteries.

2 is an enlarged cross-sectional view of a negative electrode current collector of a stacked secondary battery according to one embodiment of the present invention. As shown in FIG. 2, in the stacked secondary battery 10a according to this embodiment, the surface of the negative electrode current collector 11' on the side of the solid electrolyte layer 17 is not flat, and a large number of protrusions 11a are present on the surface. Specifically, the surface of the negative electrode current collector 11' on the side of the solid electrolyte layer 17 has irregularities with a ten-point mean roughness (R _zJIS ) in the range of 3 to 50 μm. Here, the "ten-point mean roughness (R _zJIS )" refers to the sum of the average value of the absolute values of the elevations (Yp) of the highest to fifth peaks and the average value of the absolute values of the elevations (Yv) of the lowest to fifth valley bottoms, measured in the longitudinal magnification direction from the average line of the sampled portion, by extracting only a reference length from the roughness curve in the direction of the mean line, and expressing this value in micrometers (μm). This ten-point average roughness ( _RzJIS ) was called Rz in the conventional JIS standard, but has been deleted from the current JIS standard. However, since the measurement method is described in Annex JA of JIS B 0601-2013, the values measured in accordance with this method will be adopted in the present invention.

In the embodiment shown in FIG. 2, a sputtering layer 12 (thickness 30 nm) of tin (Sn), which is a metal that can be alloyed with lithium, is provided on the surface of the negative electrode current collector 11' on the side of the solid electrolyte layer 17 as a lithium alloying metal layer.

Figure 3 is a perspective view of a stacked secondary battery according to one embodiment of the present invention. Figure 4 is a side view seen from direction A shown in Figure 3.

3 and 4, the stacked secondary battery 100 according to this embodiment includes the power generating element 21 sealed in the laminate film 29 shown in FIG. 1, two metal plates 200 that sandwich the power generating element 21 sealed in the laminate film 29, and a bolt 300 and a nut 400 as fastening members. The fastening members (bolt 300 and nut 400) have the function of fixing the power generating element 21 sealed in the laminate film 29 in a sandwiched state between the metal plates 200. As a result, the metal plates 200 and the fastening members (bolt 300 and nut 400) function as pressure members that press (restrain) the power generating element 21 in its stacking direction. The pressure members are not particularly limited as long as they are members that can press the power generating element 21 in its stacking direction. As the pressure members, a combination of a plate made of a material having rigidity such as the metal plate 200 and the above-mentioned fastening members is typically used. As for the fastening members, in addition to the bolts 300 and nuts 400, tension plates or the like that secure the ends of the metal plates 200 so as to restrain the power generating element 21 in the stacking direction may also be used.

The lower limit of the load applied to the power generating element 21 (restraint pressure in the stacking direction of the power generating element) is, for example, 0.1 MPa or more, preferably 1 MPa or more, and more preferably 5 MPa or more. The upper limit of the restraint pressure in the stacking direction of the power generating element is, for example, 100 MPa or less, preferably 90 MPa or less, and more preferably 80 MPa or less.

The main components of the stacked secondary battery 10a described above are described below.

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

Specific examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition to these, clad materials of nickel and aluminum, clad materials of copper and aluminum, etc. may also be used. Also, foils in which the metal surface is coated with aluminum may be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, etc.

The latter conductive resin includes resins in which conductive fillers are added as necessary to non-conductive polymeric materials.

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

A conductive filler can be added to the conductive polymer material or non-conductive polymer material as necessary. In particular, when the resin that serves as the base material of the collector is made of only a non-conductive polymer, a conductive filler is necessarily required to impart conductivity to the resin.

The conductive filler can be used without any particular restriction as long as it is a material having electrical conductivity. For example, metals and conductive carbon can be mentioned as materials having excellent electrical conductivity, potential resistance, or lithium ion blocking properties. There are no particular restrictions on the metal, but it is preferable that it contains at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or an alloy or metal oxide containing these metals. There are also no particular restrictions on the conductive carbon. It is preferable that it contains at least one selected from the group consisting of acetylene black, Vulcan (registered trademark), Black Pearl (registered trademark), carbon nanofiber, Ketjen Black (registered trademark), carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene.

There are no particular restrictions on the amount of conductive filler added, so long as it is an amount that can impart sufficient conductivity to the current collector, and it is generally 5 to 80% by mass relative to the total mass of the current collector (100% by mass).

The current collector may be a single layer structure made of a single material, or may be a laminate structure made of an appropriate combination of layers made of these materials. From the viewpoint of reducing the weight of the current collector, it is preferable that the current collector contains at least a conductive resin layer made of a resin having electrical conductivity. Also, from the viewpoint of blocking the movement of lithium ions between the layers of the single cells, a metal layer may be provided on part of the current collector.

There are no particular limitations on the thickness of the positive electrode current collector, but an example is 10 to 100 μm.

[Positive electrode active material layer]
The positive electrode constituting the lithium secondary battery according to this embodiment has a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions. The positive electrode active material layer 15 is typically disposed on the surface of a positive electrode current collector 11" as shown in FIG. 1, but in cases where the positive electrode active material layer 15 itself has a certain degree of conductivity, it is also possible for the positive electrode active material layer itself to constitute the positive electrode without using a positive electrode current collector.

The positive electrode active material is not particularly limited as long as it is a material that can release lithium ions during the charging process of the secondary battery and absorb lithium ions during the discharging process. An example of such a positive electrode active material includes a material that contains an M1 element and an O element, and the M1 element contains at least one element selected from the group consisting of Li, Mn, Ni, Co, Cr, Fe and P. Examples of such a positive electrode active material include layered rock salt type active materials such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and Li(Ni-Mn-Co)O ₂ , spinel type active materials such as LiMn ₂ O ₄ and LiNi _0.5 Mn _1.5 O ₄ , olivine type active materials such as LiFePO ₄ and LiMnPO ₄ , and Si-containing active materials such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ . Examples of oxide active materials other than those mentioned above include Li ₄ Ti ₅ O ₁₂ and LiVO ₂ .

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

In a preferred embodiment, the positive electrode active material layer 15 constituting the lithium secondary battery according to this embodiment contains, from the viewpoint of output characteristics, a layered rock salt type active material containing lithium and cobalt (for example, Li(Ni--Mn--Co)O ₂ ) as the positive electrode active material.

The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, the average particle size (D ₅₀ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. In this specification, the average particle size (D ₅₀ ) of the positive electrode active material can be measured by a laser diffraction scattering method.

The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 30 to 99 mass%, more preferably within the range of 40 to 90 mass%, and even more preferably within the range of 45 to 80 mass%.

In the lithium secondary battery according to this embodiment, the positive electrode active material layer 15 preferably further contains a solid electrolyte. Examples of the solid electrolyte include a sulfide solid electrolyte, a resin solid electrolyte, and an oxide solid electrolyte. As the solid electrolyte, a material having a desired bulk modulus can be appropriately selected according to the degree of volume expansion accompanying the charge and discharge of the electrode active material used.

In a preferred embodiment of the secondary battery according to the present invention, the solid electrolyte preferably includes a resin solid electrolyte, from the viewpoint of being able to better follow the volume change of the electrode active material accompanying charging and discharging. Examples of such a resin solid electrolyte include fluororesin, polyethylene oxide, polyacrylonitrile, polyacrylate, and derivatives and copolymers thereof.

Examples of fluororesins include those containing vinylidene fluoride (VdF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and derivatives of these as structural units. Specific examples include homopolymers such as polyvinylidene fluoride (PVdF), polyhexafluoropropylene (PHFP), and polytetrafluoroethylene (PTFE), and binary copolymers such as a copolymer of VdF and HFP.

In another preferred embodiment of the secondary battery according to the present invention, the solid electrolyte is preferably a sulfide solid electrolyte containing an S element, from the viewpoint of being more responsive to the volume change of the electrode active material accompanying charging and discharging, more preferably a sulfide solid electrolyte containing Li, M and S, the M element containing 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.

The sulfide solid electrolyte may have a Li ₃ PS ₄ skeleton, a Li ₄ P ₂ S ₇ skeleton, or a Li ₄ P ₂ S ₆ skeleton. Examples of sulfide solid electrolytes having a Li ₃ PS ₄ skeleton include LiI-Li ₃ PS ₄ , LiI-LiBr-Li ₃ PS _{4, and} Li ₃ PS _4. Examples of sulfide solid electrolytes having a Li ₄ P ₂ S ₇ skeleton include Li-P-S solid electrolytes called LPS. Examples of sulfide solid electrolytes include LGPS represented by Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0<x<1). More specifically, examples of the sulfide include LPS (Li ₂ S-P ₂ S ₅ ), Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S, Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP ₂ S ₁₂ , and Li ₆ PS ₅ X (wherein X is Cl, Br, or I). Note that the description "Li ₂ S-P ₂ S ₅ " means a sulfide solid electrolyte obtained by using a raw material composition containing Li ₂ S and P ₂ S ₅ , and the same applies to other descriptions. Among these, the sulfide solid electrolyte is preferably selected from the group consisting of LPS (Li ₂ S-P ₂ S ₅ ), Li ₆ PS ₅ X (wherein X is Cl, Br or I), Li ₇ P ₃ S ₁₁ , Li _3.2 P _0.96 S and Li ₃ PS ₄ , from the viewpoint that it has high ionic conductivity and a low bulk modulus and can therefore follow the volume change of the electrode active material accompanying charge and discharge.

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

(Conductive assistant and binder)
The positive electrode active material layer may further contain at least one of a conductive assistant and a binder in addition to the positive electrode active material and the solid electrolyte. However, in a preferred embodiment, the positive electrode active material layer does not contain a binder, and in a more preferred embodiment, the positive electrode active material layer does not contain a conductive assistant and a binder.

Examples of conductive assistants 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 (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). In addition, particulate ceramic materials and resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive assistants. Among these conductive assistants, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, more preferably to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon, and even more preferably to include at least one carbon. These conductive assistants may be used alone or in combination of two or more.

The conductive assistant is preferably particulate or fibrous. When the conductive assistant is particulate, the shape of the particles is not particularly limited, and may be any shape, such as powder, sphere, rod, needle, plate, column, irregular shape, scale, spindle shape, etc.

When the conductive assistant is particulate, the average particle diameter (primary particle diameter) is not particularly limited, but is preferably 0.01 to 10 μm from the viewpoint of the electrical properties of the battery. In this specification, the "particle diameter of the conductive assistant" means the maximum distance L between any two points on the contour line of the conductive assistant. The value of the "average particle diameter of the conductive assistant" is calculated as the average particle diameter of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

When the positive electrode active material layer contains a conductive assistant, the content of the conductive assistant in the positive electrode active material layer is not particularly limited, but is preferably 0 to 10 mass %, more preferably 2 to 8 mass %, and even more preferably 4 to 7 mass %, relative to the total mass of the positive electrode active material layer. Within such a range, it is possible to form a stronger electron conduction path in the positive electrode active material layer, which can effectively contribute to improving the battery characteristics.

The thickness of the positive electrode active material layer varies depending on the configuration of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

From the viewpoint of improving the energy density of the secondary battery, the porosity of the positive electrode active material layer is preferably 20% or less, more preferably 18% or less, and even more preferably 15% or less. There is no particular lower limit, but a value of 5% or more is preferable.

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

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

The solid electrolyte layer may further contain a binder in addition to the solid electrolyte described above.

The thickness of the solid electrolyte layer varies depending on the configuration of the intended all-solid-state battery, but is preferably within the range of 0.1 to 1000 μm, for example.

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

As described above with reference to FIG. 2, the negative electrode current collector 11′ is characterized in that the surface on the solid electrolyte layer 17 side has a ten-point average roughness (R _zJIS ) of 3 to 50 μm. From the viewpoints that such a roughness can be easily achieved and that the roughness can be maintained for a long period of time even under the restraining pressure applied by the pressure member, it is preferable that the material constituting the negative electrode current collector is a metal. Specific examples of metals include nickel, stainless steel, titanium, and copper. Among them, stainless steel, copper, and nickel are preferable from the viewpoints of electronic conductivity, battery operating potential, and the like.

There is no particular limit to the thickness of the negative electrode current collector, but an example is 10 to 100 μm. The value of the ten-point mean roughness (R _zJIS ) described above may be within the range of 3 to 50 μm, preferably 5 to 40 μm, and more preferably 10 to 30 μm. There is no particular limit to the method for controlling the ten-point mean roughness (R _zJIS ) value on the surface of the negative electrode current collector to a value within such a range, and a conventionally known method for roughening (roughening) the surface of a metal foil can be appropriately adopted. Examples of such roughening (roughening) treatment of the surface of a metal foil include an up method such as a granulation treatment, and a down method such as an etching treatment and a polishing treatment.

Here, according to the lithium secondary battery of this embodiment, in a lithium secondary battery including a so-called lithium precipitation type power generating element and a pressing member for pressing the power generating element with a predetermined pressure in the stacking direction, the ten-point mean roughness ( _RzJIS ) of the surface of the negative electrode current collector on the solid electrolyte layer side is controlled to the above-mentioned predetermined range, thereby making it possible to improve the charge and discharge rate characteristics. Although the mechanism is not completely clear, the above-mentioned ten-point mean roughness ( _RzJIS ) value is relatively large, at 3 μm or more, so that a sufficient space is secured between the negative electrode current collector and the solid electrolyte layer for lithium metal to precipitate during the charging process. As a result, it is considered that the increase in overvoltage during lithium metal precipitation is suppressed, and the charge and discharge rate characteristics are improved. In addition, the above-mentioned space absorbs the volume change of the negative electrode caused by lithium precipitation during the charging process to a certain extent, so that lithium metal can be uniformly precipitated on the negative electrode current collector, which is also considered to contribute to the improvement of the charge and discharge rate characteristics. In other words, it is presumed that the reason why sufficient charge/discharge rate characteristics could not be achieved even by the technology described in the above-mentioned Patent Document 1 is that the volume change of the negative electrode caused by lithium deposition during the charging process could not be sufficiently alleviated. In the lithium secondary battery according to this embodiment, the upper limit value of the above-mentioned ten-point average roughness ( _RzJIS ) is set to 50 μm or less. This is because if the value of _RzJIS exceeds 50 μm, it becomes difficult to achieve uniform deposition of lithium metal on the negative electrode current collector during the charging process.

In the lithium secondary battery according to this embodiment, the negative electrode current collector may be curved. By curving the negative electrode current collector, it may be possible to arrange a larger space for holding the lithium metal that precipitates during the charging process. There is no particular restriction on the direction of the curvature, and the center of the negative electrode current collector may protrude toward the solid electrolyte layer or may be recessed. There is also no particular restriction on the degree of curvature, but the displacement height (the maximum distance of the negative electrode current collector in the stacking direction of the power generating element) may be about 3 to 50 μm.

Furthermore, as described above with reference to FIG. 2, it is preferable that a lithium alloying metal layer (tin (Sn) sputtering layer 12 shown in FIG. 2) containing a metal that can be alloyed with lithium is disposed on the surface of the negative electrode current collector 11' on the side of the solid electrolyte layer 17. Examples of metals that can be alloyed with lithium include aluminum, magnesium, zinc, bismuth, tin, lead, indium, ruthenium, rhodium, iridium, palladium, platinum, silver, gold, cadmium, gallium, thallium, silicon, and germanium. Among these, from the viewpoint of being able to configure a battery with excellent capacity and energy density, it is preferable that the material that can be alloyed with lithium contains at least one metal selected from the group consisting of magnesium, silver, silicon, gold, indium, germanium, tin, lead, aluminum, and zinc, and more preferably contains magnesium, tin, silver, silicon, gold, or indium.

The thickness of the lithium alloying metal layer is not particularly limited, but is preferably about 10 nm to 10 μm. There is also no particular limit to the specific method for disposing the lithium alloying metal layer on the surface of the negative electrode current collector, and examples of the method include dry methods such as sputtering, as well as wet methods in which a slurry containing fine particles of a metal that can be alloyed with lithium is applied and dried.

According to the above-mentioned configuration, when the lithium secondary battery is charged, the lithium ions that reach the negative electrode side through the solid electrolyte layer are alloyed with a metal that can be alloyed with lithium. The lithium-containing alloy is then held in the space present on the surface of the negative electrode current collector. Compared to when metallic lithium is precipitated as a single substance, the precipitation energy is smaller when the lithium-containing alloy is precipitated, so by adopting the above-mentioned configuration, metallic lithium can be precipitated more uniformly. In addition, the interface resistance between the negative electrode current collector and the solid electrolyte layer is also reduced, making it possible to achieve a higher current density. As a result, the charge/discharge rate characteristics can be further improved.

As described above with reference to FIG. 1, it is preferable that a carbon layer containing non-graphite carbon is disposed on the surface of the negative electrode collector 11' on the side of the solid electrolyte layer 17. With this configuration, bulky and highly conductive carbon is disposed between the negative electrode collector and the solid electrolyte layer. As a result, the contact area between the solid electrolyte layer and the negative electrode collector can be increased while minimizing the reduction in space for lithium metal to precipitate during the charging process, thereby reducing the contact resistance at the interface between them, which in turn contributes to further improving the charge/discharge rate characteristics. If highly crystalline graphite is used for the carbon layer, it may be oriented on the negative electrode collector and easily peel off. In contrast, by using non-graphite carbon for the carbon layer, peeling of the carbon layer from the negative electrode collector can be suppressed.

Examples of non-graphite carbon used to form the carbon layer include Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), acetylene black, activated carbon, furnace black, carbon nanotubes (CNT), graphene, etc., among which Ketjen Black (registered trademark) is preferred. In the case of Ketjen Black (registered trademark), lithium ions are unlikely to be inserted between the layers, so charging and discharging is unlikely to proceed at a potential more noble than the deposition and dissolution potential of metallic lithium, which can contribute to improving the energy density of the battery. The average particle size (D50) of the non-graphite carbon is preferably within the range of 10 nm to 10 μm, for example, and more preferably within the range of 15 nm to 5 μm. The value of the average particle size of the non-graphite carbon can be calculated using a laser diffraction particle size distribution meter or measured based on image analysis using an electron microscope such as a SEM.

The carbon layer may further contain the above-mentioned solid electrolyte. The ratio of carbon to solid electrolyte in the carbon layer, in terms of the mass ratio of these two types of materials, is preferably carbon:solid electrolyte = 1:1 to 10:0, and more preferably carbon:solid electrolyte = 2:1 to 10:0. There are also no particular limitations on the method of forming the carbon layer. For example, the method may include a method of wet-coating a mixture obtained by hand mixing using a mortar and pestle, a homogenizer, mechanical milling, or the like, or the mixture may be molded into the shape of the carbon layer by powder compaction in the same manner as the positive electrode active material layer.

In the above-mentioned carbon layer, the surface of the non-graphite carbon constituting the carbon layer is preferably coated with a metal that can be alloyed with lithium. This configuration can further increase the contact area between the solid electrolyte layer and the negative electrode current collector, and can also substantially increase the electrode area, which has the advantage of further improving the charge/discharge rate characteristics. Here, an example of a form in which the "surface of the non-graphite carbon is coated with a metal that can be alloyed with lithium" is a form in which a lithium alloying metal layer containing a metal that can be alloyed with lithium is provided on the surface of the above-mentioned carbon layer on the solid electrolyte layer side. In addition, a form in which the surface of the non-graphite carbon before the carbon layer is formed is coated with a metal that can be alloyed with lithium by plating or the like to form the above-mentioned carbon layer can also be adopted.

[Positive and negative current collector plates]
The material constituting the current collector plate (25, 27) is not particularly limited, and a known highly conductive material conventionally used as a current collector plate for a secondary battery can be used. As the material constituting the current collector plate, for example, a metal material such as aluminum, carbon-coated aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof is preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the negative electrode current collector plate 25 and the positive electrode current collector plate 27, or different materials may be used.

[Positive and negative electrode leads]
Although not shown in the figures, the current collectors (11", 11') and the current collecting plates (27, 25) may be electrically connected via a positive electrode lead and a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium secondary batteries may be similarly adopted. Note that the part removed from the exterior is preferably covered with a heat-resistant insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, causing electric leakage and affecting products (e.g., automobile parts, particularly electronic devices, etc.).

[Battery exterior body]
As the battery exterior body, a known metal can case can be used, and a bag-shaped case using a laminate film 29 containing aluminum, which can cover the power generating element as shown in FIG. 1, can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is preferable from the viewpoint of being excellent in high output and cooling performance and being suitable for use in batteries for large equipment for EVs and HEVs. In addition, a laminate film containing aluminum is more preferable as the exterior body because it can easily adjust the group pressure applied to the power generating element from the outside.

5 is a perspective view showing the appearance of a stacked secondary battery according to one embodiment of the present invention. As shown in FIG. 5, the flat stacked secondary battery 50 has a rectangular flat shape, and a positive electrode tab 58 and a negative electrode tab 59 for extracting power are pulled out from both sides. The power generating element 57 is wrapped in the battery outer casing (laminate film 52) of the stacked secondary battery 50, and the periphery is heat-sealed, and the power generating element 57 is sealed in a state in which the positive electrode tab 58 and the negative electrode tab 59 are pulled out to the outside. Here, the power generating element 57 corresponds to the power generating element 21 of the stacked secondary battery 10a shown in FIG. 1 described above. The power generating element 57 is a stack of multiple single cell layers (single cells) 19 consisting of a positive electrode (positive electrode current collector 11" and positive electrode active material layer 15), a solid electrolyte layer 17, and a negative electrode (negative electrode current collector 11').

The lithium secondary battery according to this embodiment is not limited to a flat shape. A wound-type all-solid-state battery may be cylindrical, or may be a cylindrical shape that has been deformed to have a rectangular flat shape, and is not particularly limited. In the above-mentioned cylindrical shape, a laminate film may be used for the exterior body, or a conventional cylindrical can (metal can) may be used, and is not particularly limited. Preferably, the power generating element is exteriorized with an aluminum laminate film. This form can achieve weight reduction. In addition, there is no particular restriction on the removal of the tabs 58 and 59 shown in FIG. 5. The positive electrode tab 58 and the negative electrode tab 59 may be pulled out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality of tabs and taken out from each side, and are not limited to those shown in FIG. In addition, in a wound-type all-solid-state battery, a cylindrical can (metal can) may be used instead of the tabs to form the terminals.

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

[Battery pack]
A battery pack is a device that consists of multiple batteries connected together. More specifically, it is a device that uses at least two batteries and is connected in series or parallel or both. By connecting them in series or parallel, it is possible to freely adjust the capacity and voltage.

A small, removable battery pack can be formed by connecting multiple batteries in series or in parallel. Then, multiple such small, removable battery packs can be connected in series or in parallel to form a large-capacity, high-output battery pack suitable for vehicle drive power sources and auxiliary power sources that require high volumetric energy density and high volumetric output density. How many batteries are connected to form a battery pack, and how many stages of small battery packs are stacked to form a large-capacity battery pack, can be determined based on the battery capacity and output of the vehicle (electric vehicle) in which it will be installed.

[vehicle]
The lithium secondary battery according to the present embodiment has a high energy density per volume. In vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles, higher capacity and larger size are required compared to electric and portable electronic device applications. Therefore, the all-solid-state battery according to the present embodiment can be suitably used as a power source for vehicles, for example, a power source for driving a vehicle or an auxiliary power source.

Specifically, the battery or a battery pack consisting of a combination of multiple batteries can be mounted on a vehicle. In the present invention, a high-capacity battery with excellent output characteristics can be constructed, and by mounting such a battery, a plug-in hybrid electric vehicle with a long EV driving distance or an electric vehicle with a long driving distance per charge can be constructed. For example, if the battery or a battery pack consisting of a combination of multiple batteries is used in a hybrid vehicle, a fuel cell vehicle, or an electric vehicle (all of which include four-wheeled vehicles (commercial vehicles such as passenger cars, trucks, and buses, and light vehicles, etc.), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles), it can be made into a vehicle with a long driving distance. However, the use is not limited to automobiles, and it can be applied to various power sources for other vehicles, such as mobile bodies such as trains, and can also be used as a mounted power source for uninterruptible power supplies, etc.

The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the operations below were performed in a glove box. Furthermore, the tools and equipment used in the glove box were thoroughly dried beforehand.

<Comparative Example 1>
(Preparation of Positive Electrode Mixture)
A predetermined amount _{of LiNi0.8Mn0.1Co0.1O2} as a positive _electrode active material, LPS ( _Li2S - _P2S5 ) as a solid _electrolyte , and acetylene black as a conductive additive _were weighed out, and beads were further added and mixed with a roller to obtain a positive electrode mixture. The compounding ratio (mass ratio) of each component was positive electrode active material: solid electrolyte: conductive additive = 60:34:6.

(Preparation of evaluation cells)
The positive electrode mixture prepared above and a negative electrode current collector were placed opposite each other with a solid electrolyte layer interposed therebetween to prepare an evaluation cell (lithium precipitation type all-solid-state lithium secondary battery).

Specifically, 100 mg of LPS (Li ₂ S—P ₂ S ₅ ) was weighed out, placed in a ceramic tube, and the surface was smoothed. Then, a pressure of 400 MPa was applied using a fastening jig to produce a solid electrolyte pellet (φ10 mm).

Thereafter, the fastening jig was removed, a predetermined amount of the positive electrode mixture was placed on one side of the pellet, and the positive electrode active material layer was prepared by applying pressure of 200 [MPa] using the fastening jig. In addition, nickel foil (manufactured by Fukuda Metal Foil and Powder Co., Ltd., surface smooth type NIF L, thickness 20 μm) was placed as a negative electrode current collector on the other side of the pellet, and the evaluation cell was prepared by applying pressure of 100 [MPa] using the fastening jig. Then, the evaluation cell of this comparative example was prepared by constraining the evaluation cell prepared at a constraining pressure of 65 [MPa] using the fastening jig. In addition, the ten-point average roughness (R _zJIS ) of the surface of the nickel foil used here that was subjected to the roughening treatment was measured according to the method described in Appendix JA of JIS B 0601-2013, and was 2 μm. In addition, the thickness of the positive electrode active material layer was 25 μm.

(Observation of the positive electrode active material layer after charging and discharging the battery)
The all-solid-state lithium secondary battery prepared above was subjected to one cycle of charge and discharge under the following charge and discharge test conditions.

(Charge/discharge test conditions)
1) Charge/discharge conditions [Voltage range] 2.5 to 4.2 V
[Charging process] CCCV
[Discharge process] CCCV
[Charge/discharge rate] 0.05C, 0.2C or 1.0C (increased sequentially)
(After charging and discharging, rest for 30 minutes each)
2) Evaluation temperature: 298K (25°C).

The evaluation cell was charged from 2.5 V to 4.2 V at 0.05 C in a constant current/constant voltage (CCCV) mode in the charging process (lithium metal precipitates on the negative electrode current collector) in a thermostatic chamber set to the above evaluation temperature using a charge/discharge tester. Then, in the discharging process (lithium metal on the negative electrode current collector dissolves), the cell was discharged from 4.2 V to 2.5 V at 0.05 C in a constant current/constant voltage (CCCV) mode. If no abnormality (sudden drop in capacity) was observed during charging/discharging at 0.05 C, a similar charge/discharge test was performed at a rate of 0.2 C. If no abnormality was observed during charging/discharging at 0.2 C, a similar charge/discharge test was performed at a rate of 1.0 C. Here, 1 C refers to the current value at which the battery is fully charged (100% charged) when charged for 1 hour at that current value.

As a result of the above, in this comparative example, a rapid decrease in capacity was confirmed during the charging process at 0.05C, and the charge/discharge test was discontinued. This is thought to be because the use of a smooth-surface type negative electrode current collector meant that there was insufficient space between the negative electrode current collector and the solid electrolyte layer for lithium metal to precipitate during the charging process, resulting in an increase in overvoltage during lithium metal precipitation. It is also thought that lithium precipitation during the charging process caused a change in the volume of the negative electrode, preventing lithium metal from being uniformly precipitated on the negative electrode current collector.

<Comparative Example 2>
An evaluation cell for this comparative example (lithium precipitation-type all-solid-state lithium secondary battery) was produced in the same manner as in Comparative Example 1 described above, except that a sputtering layer (thickness 30 nm) made of magnesium, which is a metal that can be alloyed with lithium, was formed by sputtering on the surface of the above-mentioned nickel foil on the solid electrolyte layer side, and used as a negative electrode current collector.

The evaluation cell prepared above was subjected to a charge/discharge test using the same method as above. As a result, a rapid decrease in capacity was confirmed during the charging process at 0.05 C in this comparative example as well, so the charge/discharge test was discontinued.

Example 1
Except for using nickel foil (surface roughened type NIF-MT, thickness 20 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.) as the negative electrode current collector, an evaluation cell (lithium precipitation type all-solid-state lithium secondary battery) of this example was produced in the same manner as in Comparative Example 1 described above. The ten-point average roughness (R _zJIS ) of the roughened surface of the nickel foil used here was measured according to the method described in Appendix JA of JIS B 0601-2013 and was found to be 10 μm.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge test at 0.05C, but a sudden decrease in capacity was confirmed during the charging process at 0.2C, so the charge/discharge test was stopped at that point.

Example 2
An evaluation cell of this example (lithium precipitation type all-solid-state lithium secondary battery) was produced in the same manner as in Example 1 described above, except that a sputtering layer (thickness 30 nm) made of magnesium, which is a metal that can be alloyed with lithium, was formed by sputtering on the surface of the above-mentioned nickel foil on the solid electrolyte layer side, and used as a negative electrode current collector.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge tests at 0.05C and 0.2C, but a sudden decrease in capacity was observed during the charging process at 1.0C, so the charge/discharge test was stopped at that point.

Example 3
An evaluation cell of this example (lithium precipitation type all-solid-state lithium secondary battery) was produced in the same manner as in Example 2 described above, except that a sputtering layer was formed on the surface of the negative electrode current collector using tin instead of magnesium as a metal that can be alloyed with lithium.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge tests at 0.05C and 0.2C, but a sudden decrease in capacity was observed during the charging process at 1.0C, so the charge/discharge test was stopped at that point.

Example 4
An evaluation cell of this example (lithium precipitation type all-solid-state lithium secondary battery) was produced in the same manner as in Example 2 described above, except that silver was used instead of magnesium as a metal capable of being alloyed with lithium to form a sputtering layer on the surface of the negative electrode current collector.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge tests at 0.05C and 0.2C, but a sudden decrease in capacity was observed during the charging process at 1.0C, so the charge/discharge test was stopped at that point.

Example 5
An evaluation cell of this example (lithium precipitation type all-solid-state lithium secondary battery) was produced in the same manner as in Example 1 described above, except that a carbon layer containing Ketjen Black (registered trademark) and a solid electrolyte was formed on the surface of the nickel foil on the solid electrolyte layer side and used as a negative electrode current collector.

Specifically, first, Ketjen Black (registered trademark) (manufactured by Lion Specialty Chemicals, ECP600JD:KB, D50 = 34 nm) and solid electrolyte (LPS) were weighed out to a mass ratio of Ketjen Black (registered trademark):LPS = 2:1, mixed by hand, added with heptane, and mixed for 3 minutes using a homogenizer (manufactured by SMT Corporation, UH-50) to obtain a mixture. Next, the obtained mixture was uniformly applied to the surface of the nickel foil on the solid electrolyte layer side, and dried to form a carbon layer. The carbon layer had a thickness of 20 μm.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge tests at 0.05C and 0.2C, but a sudden decrease in capacity was observed during the charging process at 1.0C, so the charge/discharge test was stopped at that point.

Example 6
An evaluation cell of this example (lithium deposition-type all-solid-state lithium secondary battery) was produced in the same manner as in Example 5 described above, except that a tin sputtering layer was further formed on the exposed surface (the surface on the solid electrolyte layer side) of the carbon layer by using the same method as in Example 3 described above.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in any of the charge/discharge tests at 0.05C, 0.2C, and 1.0C.

Example 7
An evaluation cell of this example (lithium deposition type all-solid-state lithium secondary battery) was produced in the same manner as in Example 3 described above, except that a carbon layer was further formed on the exposed surface (the surface on the solid electrolyte layer side) of the tin sputtering layer by using the same method as in Example 5 described above.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in the charge/discharge tests at 0.05C and 0.2C, but a sudden decrease in capacity was observed during the charging process at 1.0C, so the charge/discharge test was stopped at that point.

Example 8
An evaluation cell of this example (lithium deposition-type all-solid-state lithium secondary battery) was produced in the same manner as in Example 7 described above, except that a tin sputtering layer was further formed on the exposed surface (the surface on the solid electrolyte layer side) of the carbon layer by using the same method as in Example 3 described above.

The evaluation cell prepared above was subjected to a charge/discharge test in the same manner as above. As a result, in this example, no sudden decrease in capacity was observed in any of the charge/discharge tests at 0.05C, 0.2C, and 1.0C.

The above results are summarized in Table 1 below.

From the results shown in the above examples and comparative examples, it can be seen that the configuration according to the present invention can improve the charge/discharge rate characteristics of lithium precipitation type lithium secondary batteries. This is believed to be because the use of a surface-roughened type negative electrode current collector ensures sufficient space between the negative electrode current collector and the solid electrolyte layer for lithium metal to precipitate during the charging process, thereby suppressing the increase in overvoltage during lithium metal precipitation. In addition, the above-mentioned space is believed to have absorbed to some extent the volume change of the negative electrode caused by lithium precipitation during the charging process, thereby achieving uniform precipitation of lithium metal on the negative electrode current collector.

Furthermore, it has been found that the charge/discharge rate characteristics can be further improved by providing a layer containing a metal that can be alloyed with lithium or a carbon layer containing non-graphitic carbon on the surface of the negative electrode current collector.

10a, 50, 100 Stacked secondary battery,
11' negative electrode current collector,
11" positive electrode current collector,
11a convex portion,
12 Tin (Sn) sputtering layer,
13 carbon layer,
15 positive electrode active material layer,
17 solid electrolyte layer,
19 cell layer,
21, 57 Power generating element,
25 negative electrode current collector (negative electrode tab),
27 Positive electrode current collector (positive electrode tab),
29, 52 Laminate film,
58 positive electrode tab,
59 negative electrode tab,
200 metal plate,
300 volts,
400 Nut.

Claims (5)

a positive electrode having a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions;
a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging;
a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte containing an S element ;
and a pressure member that applies a predetermined pressure to the power generating element in a stacking direction,
a ten-point average roughness (R _zJIS ) of a surface of the negative electrode current collector on the side of the solid electrolyte layer is more than 10 μm and not more than 50 μm. The lithium secondary battery according to claim 1, wherein a lithium alloying metal layer containing a metal capable of being alloyed with lithium is disposed on the surface of the negative electrode current collector facing the solid electrolyte layer. The lithium secondary battery according to claim 1 or 2, wherein a carbon layer containing non-graphite carbon is disposed on the surface of the negative electrode current collector facing the solid electrolyte layer. The lithium secondary battery according to claim 3, wherein the surface of the non-graphitic carbon is coated with a metal capable of alloying with lithium. 5. _The lithium secondary _battery according _to claim 1, wherein the solid electrolyte contained in the solid electrolyte layer is selected from the group consisting of _Li2S - _P2S5 , _Li6PS5X (wherein X is Cl, Br or I ₎ , _Li7P3S11 , _{Li3.2P0.96S and Li3PS4 .}