Secondary battery

Abstract

The present invention provides a means which is capable of improving the charge capacity during high-rate charge of a secondary battery that is provided with a solid electrolyte layer. The present invention provides a secondary battery which is provided with: a positive electrode that is obtained by arranging a positive electrode active material layer on the surface of a positive electrode collector; a negative electrode that is obtained by arranging a negative electrode active material layer on the surface of a negative electrode collector; and a first solid electrolyte layer and a second solid electrolyte layer, each of which contains a solid electrolyte and a binder. With respect to this secondary battery, the positive electrode and the negative electrode are arranged so as to face each other in such a manner that the first solid electrolyte layer and the second solid electrolyte layer are sandwiched between the positive electrode active material layer and the negative electrode active material layer; the first solid electrolyte layer is arranged on the positive electrode active material layer side, while the second solid electrolyte layer is arranged on the negative electrode active material layer side; the thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer; and the ratio (A / B) of the binder concentration (A) (% by mass) relative to the total solid content in the first solid electrolyte layer to the binder concentration (B) (% by mass) relative to the total solid content in the second solid electrolyte layer satisfies 1 < A / B ≤ 4.5.

Description

secondary battery

[0001] The present invention relates to a secondary battery using a solid electrolyte.

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

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

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

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

[0006] In recent years, there has been an increasing need for higher energy density in all-solid-state secondary batteries, and this has led to a demand for thinner solid electrolyte layers. However, thinning the solid electrolyte layer in all-solid-state lithium secondary batteries can cause short circuits. The technology disclosed in International Publication No. 2020 / 166165 addresses this issue by providing a first solid electrolyte layer and a second solid electrolyte layer in the all-solid-state secondary battery. This all-solid-state secondary battery is characterized in that the thickness and organic compound content of the first solid electrolyte layer are smaller than those of the second solid electrolyte layer.

[0007] However, according to the investigations of the present inventors, it has been found that the technology described in WO 2020 / 166165 may not achieve sufficient charge capacity when a secondary battery equipped with a solid electrolyte layer is rapidly charged.

[0008] Therefore, an object of the present invention is to provide a means for improving the charge capacity during rapid charging in a secondary battery having a solid electrolyte layer.

[0009] The present inventors conducted extensive research to solve the above-mentioned problems, and as a result, they found that the above-mentioned problems can be solved by providing two solid electrolyte layers in a secondary battery using a solid electrolyte, making the thickness of the first solid electrolyte layer located on the positive electrode side smaller than the thickness of the second solid electrolyte layer located on the negative electrode side, and further making the binder concentration contained in the first solid electrolyte layer higher than the binder concentration of the second solid electrolyte layer within a specific range, thereby completing the present invention.

[0010] That is, one aspect of the present invention relates to a secondary battery including a positive electrode having a positive electrode active material layer disposed on a surface of a positive electrode current collector, a negative electrode having a negative electrode active material layer disposed on a surface of a negative electrode current collector, and first and second solid electrolyte layers each containing a solid electrolyte and a binder, wherein the positive electrode and the negative electrode are disposed such that the positive electrode active material layer and the negative electrode active material layer sandwich the first and second solid electrolyte layers, the first solid electrolyte layer is disposed on the positive electrode active material layer side, and the second solid electrolyte layer is disposed on the negative electrode active material layer side, the thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, and a ratio (A / B) of a concentration (A) [mass %] of the binder relative to the total solid content of the first solid electrolyte layer to a concentration (B) [mass %] of the binder relative to the total solid content of the second solid electrolyte layer satisfies 1<A / B≦4.5.

[0011] Fig. 1 is a perspective view showing the appearance of a flat stacked secondary battery according to one embodiment of the present invention. Fig. 2 is a cross-sectional view taken along line 2-2 shown in Fig. 1. Fig. 3 is a schematic view showing an enlarged cross section of a cell layer constituting a power generating element of the stacked secondary battery shown in Figs. 1 and 2.

[0012] One aspect of the present invention is a secondary battery comprising: a positive electrode having a positive electrode active material layer disposed on a surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer disposed on a surface of a negative electrode current collector; and first and second solid electrolyte layers each containing a solid electrolyte and a binder, wherein the positive electrode and the negative electrode are disposed opposite each other such that the positive electrode active material layer and the negative electrode active material layer sandwich the first and second solid electrolyte layers, the first solid electrolyte layer facing the positive electrode active material layer and the second solid electrolyte layer facing the negative electrode active material layer, the thickness of the first solid electrolyte layer being smaller than the thickness of the second solid electrolyte layer, and a ratio (A / B) of a binder concentration (A) [mass %] relative to the total solid content of the first solid electrolyte layer to a binder concentration (B) [mass %] relative to the total solid content of the second solid electrolyte layer being 1 < A / B ≦ 4.5. According to this aspect, the charge capacity during rapid charging of a secondary battery including a solid electrolyte layer can be improved.

[0013] The present embodiment will be described below with reference to the drawings. However, the technical scope of the present invention should be defined based on the claims and is not limited to the following embodiments. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios. The present invention will be described below using a stacked-type (internal parallel connection) all-solid-state lithium secondary battery, which is one type of secondary battery, as an example. All-solid-state lithium secondary batteries have the advantage that, in principle, they do not encounter problems caused by flammable organic electrolytes, as in conventional liquid-based lithium secondary batteries. Furthermore, they also have the advantage that the use of high-potential, large-capacity positive electrode materials and large-capacity negative electrode materials can significantly improve the output density and energy density of the battery.

[0014] FIG. 1 is a perspective view showing the appearance of a flat-layered all-solid-state lithium secondary battery according to one embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 . The layered structure allows the battery to be compact and have a high capacity. This specification will be described in detail using the flat-layered, non-bipolar all-solid-state lithium secondary battery shown in FIGS. 1 and 2 (hereinafter simply referred to as a "layered secondary battery"). However, in terms of the internal electrical connection configuration (electrode structure) of the secondary battery according to this embodiment, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0015] 1, the stacked secondary battery 10a has a flat, rectangular shape, and a negative electrode current collector 25 and a positive electrode current collector 27 for extracting power are pulled out from both sides of the stacked secondary battery 10a. The power generating element 21 is wrapped in a battery exterior material (laminate film 29) of the stacked secondary battery 10a, and the periphery is heat-sealed, with the negative electrode current collector 25 and the positive electrode current collector 27 pulled out to the outside.

[0016] As shown in FIG. 2 , the stacked secondary battery 10 a of this embodiment has a structure in which a flat, generally rectangular power generating element 21, in which charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the power generating element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are laminated. The positive electrode has a structure in which positive electrode active material layers 15 containing a positive electrode active material are disposed on both sides of a positive electrode current collector 11″. The negative electrode has a structure in which negative electrode active material layers 13 containing a negative electrode active material are disposed on both sides of a negative electrode current collector 11′. The solid electrolyte layer 17 is composed of two layers, a first solid electrolyte layer and a second solid electrolyte layer, as will be described later.

[0017] A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative and positive electrodes) are attached to the negative electrode current collector 11′ and the positive electrode current collector 11″, respectively, and are configured to be sandwiched between the ends of the laminate film 29 and led out of the laminate film 29. The negative electrode current collector 25 and the positive electrode current collector 27 may be attached to the negative electrode current collector 11′ and the positive electrode current collector 11″ of the respective electrodes by ultrasonic welding, resistance welding, or the like, via a negative electrode terminal lead and a positive electrode terminal lead (not shown), respectively, as necessary.

[0018] Fig. 3 is a schematic diagram showing an enlarged cross section of the cell layer 19 constituting the power generating element 21 of the stacked secondary battery 10a shown in Fig. 1 and Fig. 2. As shown in Fig. 3, in the cell layer 19, the positive electrode active material layer 15 and the negative electrode active material layer 13 are arranged to sandwich the first solid electrolyte layer 17a and the second solid electrolyte layer 17b, with the first solid electrolyte layer 17a being arranged on the positive electrode active material layer 15 side and the second solid electrolyte layer 17b being arranged on the negative electrode active material layer 13 side. In other words, the cell layer 19 has a configuration in which the positive electrode current collector 11", the positive electrode active material layer 15, the first solid electrolyte layer 17a, the second solid electrolyte layer 17b, the negative electrode active material layer 13, and the negative electrode current collector 11' are laminated in this order. The thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, and the ratio (A / B) of the binder concentration (A) [mass %] with respect to the total solid content of the first solid electrolyte layer to the binder concentration (B) [mass %] with respect to the total solid content of the second solid electrolyte layer is 1<A / B≦4.5.

[0019] The secondary battery according to the present invention has the above-described configuration, and is provided with a solid electrolyte layer, and can improve the charge capacity during rapid charging. Although the details of why this effect is achieved are unclear, the following mechanism is thought to be involved.

[0020] For example, when a secondary battery such as a lithium secondary battery is charged, lithium is released from the positive electrode active material, which can cause the positive electrode active material layer to shrink. In recent years, there has been an increasing need for rapid charging of secondary batteries, but it is known that rapid charging of secondary batteries reduces their charge capacity. According to the inventors' investigations, it has been found that the decrease in charge capacity occurs because the positive electrode active material layer rapidly shrinks when the secondary battery is rapidly charged, causing peeling at the interface between the positive electrode active material layer and the solid electrolyte layer.

[0021] In the secondary battery according to the present invention, the binder concentration in the first solid electrolyte layer is higher than the binder concentration in the second solid electrolyte layer. Therefore, a large amount of binder is present in the surface layer of the first solid electrolyte layer. These binders bind to the cathode active material, solid electrolyte, conductive additive, binder, etc. present in the surface layer of the cathode active material layer, thereby increasing the adhesive strength between the first solid electrolyte layer and the cathode active material layer and preventing delamination of the two layers. Furthermore, the first solid electrolyte layer has a small thickness, which prevents a decrease in ionic conductivity. Furthermore, the second solid electrolyte layer provided together with the first solid electrolyte layer has a large thickness, which prevents short-circuiting of the secondary battery due to the formation of dendrites or cracks in the solid electrolyte layer. Furthermore, the second solid electrolyte layer has a low binder concentration, which allows it to maintain high ionic conductivity even when the layer is thick. As described above, in the secondary battery according to the present invention, by increasing the adhesion between the positive electrode active material layer and the solid electrolyte layer, peeling of the two layers is prevented, while short-circuiting due to the generation of dendrites and the like is prevented, and further, the ionic conductivity of the solid electrolyte layer can be maintained, which is thought to enable an improvement in charge capacity during rapid charging.

[0022] In the stacked secondary battery 10a according to this embodiment, the power generating element 21 sealed in the laminate film 29 shown in FIG. 1 is preferably sandwiched between two plate-shaped members and further fastened using a fastening member. As a result, the plate-shaped members and fastening members function as pressure members that pressurize (restrain) the power generating element 21 in the stacking direction. Examples of the plate-shaped members include metal plates and resin plates. Examples of the fastening members include bolts and nuts. However, the pressure members are not particularly limited as long as they can pressurize the power generating element 21 in the stacking direction. A typical pressure member is a combination of a plate made of a rigid material, like the plate-shaped members, and the fastening members described above. Furthermore, the fastening members may be not only bolts and nuts, but also tension plates or the like that secure the ends of the plate-shaped members so as to restrain the power generating element 21 in the stacking direction. The lower limit of the load applied to the power generating element 21 (constraint pressure in the stacking direction of the power generating element) is, for example, 0.1 MPa or more, preferably 0.5 MPa or more, more preferably 1 MPa or more, and even more preferably 3 MPa or more. The upper limit of the constraint pressure in the stacking direction of the power generating element is, for example, 100 MPa or less, preferably 70 MPa or less, more preferably 40 MPa or less, and even more preferably 10 MPa or less.

[0023] The main components of the secondary battery according to the present invention, which has been described above using the stacked secondary battery 10a as an example, will now be described.

[0024] [Current Collectors] The current collectors (negative electrode current collector 11′ and positive electrode current collector 11″) have a function of mediating the transfer of electrons from the electrode active material layer. There are no particular limitations on the material constituting the current collectors. As the material constituting the current collectors, for example, metals and conductive resins can be used.

[0025] Specifically, examples of metals include aluminum, nickel, iron, stainless steel, titanium, and copper. In addition, a clad material of nickel and aluminum, a clad material of copper and aluminum, and the like may also be used. Furthermore, a foil in which a metal surface is coated with aluminum may also be used. Among these, aluminum, stainless steel, copper, and nickel are preferred from the viewpoints of electronic conductivity, battery operating potential, and adhesion of active materials.

[0026] The latter conductive resin may be a conductive polymer material or a non-conductive polymer material to which a conductive filler is added as needed.

[0027] The current collector may have a single layer structure made of a single material, or may have 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 includes at least a conductive resin layer made of a resin having conductivity.

[0028] [Negative Electrode Active Material Layer] The negative electrode active material layer contains a negative electrode active material. The type of negative electrode active material is not particularly limited, but includes carbon materials, metal oxides, and metal active materials. Furthermore, a lithium-containing metal may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it is a lithium-containing active material, and examples thereof include metallic lithium and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. The negative electrode active material preferably contains metallic lithium or a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and particularly preferably contains metallic lithium or a lithium-containing alloy. When metallic lithium or a lithium-containing alloy is used as the negative electrode active material, the secondary battery according to this embodiment may be a so-called lithium deposition type in which metallic lithium is deposited on the negative electrode current collector during charging. Therefore, in this configuration, the thickness of the negative electrode active material layer increases as the charging process progresses and decreases as the discharging process progresses. The negative electrode active material layer does not need to be present during full discharge, but in some cases, a negative electrode active material layer made of a certain amount of metallic lithium may be present during full discharge.

[0029] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably within a range of 40 to 100 mass %, and more preferably within a range of 50 to 90 mass %, for example.

[0030] The negative electrode active material layer may further contain a solid electrolyte as needed. By including a solid electrolyte in the negative electrode active material layer, the ionic conductivity of the negative electrode active material layer can be improved. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes. In this specification, the term "solid electrolyte" refers to a material mainly composed of an ion conductor capable of ion conduction in a solid, and in particular, a material having a lithium ion conductivity of 1×10 at room temperature (25° C.). −５ S / cm or more, and this lithium ion conductivity is preferably 1×10 −４The ionic conductivity is 200 S / cm or more. Here, the value of the ionic conductivity can be measured by an AC impedance method.

[0031] From the viewpoint of exhibiting excellent lithium ion conductivity, the solid electrolyte is preferably a sulfide solid electrolyte containing an S element, more preferably a sulfide solid electrolyte containing a Li element, an M element, and an S element, wherein the M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I, and even more preferably a sulfide solid electrolyte containing an S element, a Li element, and a P element.

[0032] The sulfide solid electrolyte is Li ３ P.S. ４ It may have a Li framework. ４ P ２ S ７ It may have a Li framework. ４ P ２ S ６ It may have a Li skeleton. ３ P.S. ４ Examples of sulfide solid electrolytes having a framework include LiI-Li ３ P.S. ４ , LiI-LiBr-Li ３ P.S. ４ , Li ３ P.S. ４ In addition, Li ４ P ２ S ７ Examples of sulfide solid electrolytes having a skeleton include Li-P-S solid electrolytes called LPS. （４−ｘ） Ge （１−ｘ） P ｘ S ４ (x satisfies 0<x<1) or the like. More specifically, for example, LPS (Li ２ S-P ２ S ５ ), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S., Li. ３．２５ Ge ０．２５ P０．７５ S ４ , Li １０ GeP ２ S １２ , or Li ６ P.S. ５ X (wherein X is Cl, Br or I). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions. Among them, the sulfide solid electrolyte is preferably LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (argyrodite-type solid electrolyte, where X is Cl, Br, or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li ３ P.S. ４ is selected from the group consisting of:

[0033] Examples of the shape of the solid electrolyte include particulate shapes such as spherical and oval spheres, and thin films. When the solid electrolyte is particulate, its average particle diameter (D50) is not particularly limited, but is preferably 40 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle diameter (D50) is preferably 0.01 μm or more, and more preferably 0.1 μm or more.

[0034] The content of the solid electrolyte in the negative electrode active material layer is, for example, preferably in the range of 1 to 60 mass %, and more preferably in the range of 10 to 50 mass %.

[0035] The negative electrode active material layer may further contain at least one of a binder and a conductive additive in addition to the above-mentioned negative electrode active material and solid electrolyte. The thickness of the negative electrode active material layer varies depending on the configuration of the intended secondary battery, but is preferably within a range of, for example, 0.1 to 1000 μm, and more preferably 40 to 100 μm.

[0036] [Solid Electrolyte Layer] In the secondary battery according to this embodiment, the solid electrolyte layer comprises a first solid electrolyte layer and a second solid electrolyte layer, each containing a solid electrolyte and a binder. In this secondary battery according to this embodiment, the first solid electrolyte layer is disposed on the cathode active material layer side, and the second solid electrolyte layer is disposed on the anode active material layer side, the thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, and the ratio (A / B) of the binder concentration (A) [mass %] relative to the total solid content of the first solid electrolyte layer to the binder concentration (B) [mass %] relative to the total solid content of the second solid electrolyte layer is 1<A / B≦4.5.

[0037] The solid electrolyte contained in the first solid electrolyte layer and the second solid electrolyte layer is not particularly limited, and the solid electrolytes exemplified in the section on the negative electrode active material layer and their preferred forms can be similarly adopted. Among them, the solid electrolyte contained in the solid electrolyte layer is preferably a sulfide solid electrolyte from the viewpoint of high ionic conductivity, and an argyrodite-type solid electrolyte (Li ６ P.S. ５ X (wherein X is Cl, Br, or I) is more preferable. Furthermore, the solid electrolyte contained in the solid electrolyte layer may be a solid electrolyte other than the solid electrolytes exemplified in the section on the negative electrode active material layer. The first solid electrolyte layer and the second solid electrolyte layer may contain the same type of solid electrolyte, or may contain solid electrolytes of different types. According to a preferred embodiment, the first solid electrolyte layer and the second solid electrolyte layer contain the same type of solid electrolyte.

[0038] The content of the solid electrolyte in each of the first solid electrolyte layer and the second 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 layers. The content of the solid electrolyte in the first solid electrolyte layer and the second solid electrolyte layer may be the same as or different from each other.

[0039] The binder contained in each of the first solid electrolyte layer and the second solid electrolyte layer is not particularly limited, but is preferably a substance that is stable within the potential range of charge / discharge operation, and furthermore, from the viewpoint of the strength of the solid electrolyte layer and adhesion to the positive electrode active material layer, is preferably selected from the group consisting of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), acrylic resin, and polytetrafluoroethylene (PTFE), more preferably selected from the group consisting of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR). Note that the binders contained in the first solid electrolyte layer and the second solid electrolyte layer may be the same or different from each other.

[0040] As described above, the solid electrolyte and binder contained in the first solid electrolyte layer and the second solid electrolyte layer may be the same or different. However, in a secondary battery according to one embodiment, it is preferable that the solid electrolyte contained in the first solid electrolyte layer and the solid electrolyte contained in the second solid electrolyte layer are the same, and the binder contained in the first solid electrolyte layer and the binder contained in the second solid electrolyte layer are the same. This makes it possible to more effectively improve the charge capacity when the secondary battery is fast charged.

[0041] The binder concentration (A) of the first solid electrolyte layer is preferably greater than 3 mass% and less than 15 mass%, more preferably 4 mass% to 10 mass%, and even more preferably 5 mass% to 8 mass%, relative to the total mass of the first solid electrolyte layer. Having the binder concentration (A) of the first solid electrolyte layer within the above range allows the solid electrolyte layer to maintain sufficient ionic conductivity while sufficiently improving adhesion to the positive electrode active material layer. The binder concentration (B) of the second solid electrolyte layer is preferably greater than 1 mass% and less than 10 mass%, more preferably 2 mass% to 6 mass%, and even more preferably 2.5 mass% to 4 mass%, relative to the total mass of the second solid electrolyte layer. Having the binder concentration (B) of the second solid electrolyte layer within the above range allows the solid electrolyte layer to maintain sufficient strength and ionic conductivity.

[0042] The ratio ((A) / (B)) of the concentration (A) of the binder contained in the first solid electrolyte layer to the concentration (B) of the binder contained in the second solid electrolyte layer is 1<A / B≦4.5, preferably 1.2≦A / B≦4.0, more preferably 1.5≦A / B≦3.5, and even more preferably 1.8≦A / B≦3.0. By having the binder concentration ratio in the above range, the charge capacity during rapid charging can be more sufficiently improved.

[0043] The thickness (a) of the first solid electrolyte layer is not particularly limited as long as it is smaller than the thickness of the second solid electrolyte layer and does not impair the performance of the intended secondary battery. For example, the thickness (a) of the first solid electrolyte layer is preferably 0.1 μm or more and 5 μm or less, more preferably 0.5 μm or more and 3 μm or less, and even more preferably 1 μm or more and 2 μm or less. On the other hand, the thickness (b) of the second solid electrolyte layer is also not particularly limited as long as it is larger than the thickness of the first solid electrolyte layer and does not impair the performance of the intended secondary battery. For example, the thickness (b) of the second solid electrolyte layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less. By having the thicknesses of the first solid electrolyte layer and the second solid electrolyte layer within the above ranges, it is possible to prevent short-circuiting of the secondary battery and improve the charge capacity during rapid charging while maintaining a high energy density of the secondary battery.

[0044] The ratio (b / a) of the thickness (b) of the second solid electrolyte layer to the thickness (a) of the first solid electrolyte layer is preferably 1<b / a≦50, more preferably 5≦b / a≦40, and even more preferably 15≦b / a≦35. When the thickness ratio is within the above range, the charge capacity when the secondary battery is rapidly charged can be more sufficiently improved.

[0045] [Positive Electrode Active Material Layer] In the secondary battery according to this embodiment, the positive electrode active material layer is a layer containing a positive electrode active material.

[0046] The type of the positive electrode active material is not particularly limited, but LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ Examples include:

[0047] The positive electrode active material layer preferably contains a positive electrode active material that shrinks during charging, and in particular, the positive electrode active material preferably contains a composite oxide containing lithium and nickel, which can further enhance the effects of the present invention. Generally, when the positive electrode active material shrinks, the solid electrolyte layer peels off from the positive electrode active material layer. However, in the secondary battery according to the present invention, the first solid electrolyte layer firmly adheres to the positive electrode active material layer, preventing peeling. Positive electrode active materials that are composite oxides containing lithium and nickel are characterized by particularly large shrinkage during charging. However, even when such positive electrode active materials are used, the secondary battery according to the present invention can suppress peeling between the positive electrode active material layer and the solid electrolyte layer.

[0048] More preferably, Li(Ni-Mn-Co)O ２ and those in which some of these transition metals have been substituted with other elements (hereinafter also referred to simply as "NMC composite oxides") are used as positive electrode active materials. NMC composite oxides have a layered crystal structure in which lithium atomic layers and transition metal (Mn, Ni, and Co) atomic layers (orderly arranged) are alternately stacked with oxygen atomic layers interposed therebetween, and contain one Li atom per atom of the transition metal M. The amount of Li that can be extracted is twice that of spinel-based lithium manganese oxides, i.e., the supply capacity is doubled, resulting in high capacity. As described above, NMC composite oxides also include composite oxides in which some of the transition metal elements have been substituted with other metal elements. In this case, other elements include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu, Ag, and Zn, and preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr.

[0049] More preferably, the general formula (1): Li ａ Ni ｂ Mn ｃ Co ｄM ｘ O ２ (wherein, a, b, c, d, and x satisfy 0.98≦a≦1.2, 0.6≦b≦0.9, 0<c≦0.4, 0<d≦0.4, 0≦x≦0.3, and b+c+d+x=1; and M is at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr), an NMC composite oxide having a composition represented by the formula (wherein a, b, c, d, and x satisfy 0.98≦a≦1.2, 0.6≦b≦0.9, 0<c≦0.4, 0<d≦0.4, 0≦x≦0.3, and b+c+d+x=1) is used as the positive electrode active material. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. From the viewpoint of achieving a high theoretical discharge capacity, it is preferable that b satisfies 0.6≦b≦0.9 as described above. However, from the viewpoint of improving the adhesion between the positive electrode active material layer and the solid electrolyte layer and suppressing an increase in the interfacial resistance between them, it is more preferable that b satisfies 0.6≦b≦0.8. Such NMC composite oxides with a high nickel content have a high capacity and also exhibit large expansion and contraction due to charge and discharge reactions, which can particularly significantly increase the interfacial resistance described above. Therefore, by using an NMC composite oxide with a high nickel content as the positive electrode active material, the effects of the present invention can be further exhibited.

[0050] In addition, a sulfur-based positive electrode active material is also one of the preferred embodiments. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0051] In some cases, two or more positive electrode active materials may be used in combination. Of course, positive electrode active materials other than those mentioned above may also be used.

[0052] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle size (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. ５０ The value of can be measured by a laser diffraction scattering method.

[0053] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably more than 50% by mass, more preferably in the range of more than 50% by mass to 95% by mass or less, and even more preferably in the range of 60% by mass to 90% by mass, relative to 100% by mass of the total solid content contained in the positive electrode active material layer.

[0054] In the secondary battery according to this embodiment, the positive electrode active material layer may contain a solid electrolyte in addition to the positive electrode active material. The type of solid electrolyte contained in the positive electrode active material layer is not particularly limited, but it is more preferable that the positive electrode active material layer contains a sulfide solid electrolyte. Specific and preferred forms of the solid electrolyte, such as the sulfide solid electrolyte, may be the same as those described in the section on the negative electrode (negative electrode active material layer) above.

[0055] The content of the solid electrolyte in the positive electrode active material layer is preferably 1% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 50% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less, relative to 100% by mass of the total solid content in the positive electrode active material layer. When the content of the solid electrolyte in the positive electrode active material layer is within the above range, both the ionic conductivity and the energy density of the positive electrode active material layer can be achieved.

[0056] The positive electrode active material layer may further contain at least one of a binder and a conductive additive in addition to the above-mentioned positive electrode active material and solid electrolyte. The thickness of the positive electrode active material layer varies depending on the configuration of the intended secondary battery, but is preferably within a range of 0.1 to 1000 μm, more preferably 40 to 100 μm.

[0057] [Intermediate Layer] The secondary battery according to one embodiment of the present invention may have an intermediate layer containing a carbon material between the negative electrode active material layer and the second solid electrolyte layer. By having such an intermediate layer, it is possible to suppress short circuits caused by the generation of dendrites in the secondary battery and to more sufficiently improve the charge capacity during rapid charging.

[0058] The carbon material is not particularly limited, and examples thereof include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, carbon black is preferred, and at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black is more preferred.

[0059] The content of the carbon material in the intermediate layer is not particularly limited, but is preferably in the range of 50 to 100 mass %, more preferably in the range of 60 to 100 mass %, and even more preferably in the range of 70 to 100 mass %.

[0060] In addition to the carbon material, the intermediate layer may also contain nanoparticles containing one or more elements selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc.

[0061] The thickness of the intermediate layer is not particularly limited, but is preferably in the range of 1 to 50 μm, more preferably in the range of 5 to 40 μm, even more preferably in the range of 10 to 30 μm, and most preferably in the range of 5 to 15 μm. When the thickness of the intermediate layer is 1 μm or more, short circuits due to the generation of dendrites can be further suppressed. When the thickness of the carbon-containing layer is 50 μm or less, a decrease in energy density can be suppressed.

[0062] [Positive Electrode Current Collector Plate and Negative Electrode Current Collector Plate] The material constituting the current collector plate is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as the constituent material of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive electrode current collector plate 27 and the negative electrode current collector plate 25 may be made of the same material or different materials.

[0063] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collector and the current collector plate may be electrically connected via a positive electrode lead or a negative electrode lead. Materials used in known lithium secondary batteries may be similarly employed as the constituent materials of the positive electrode and negative electrode lead. It is preferable that the portion removed from the exterior be covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting products (e.g., automotive parts, particularly electronic devices).

[0064] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element can be used, as shown in Figures 1 and 2 . 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 desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable for the exterior body because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0065] The secondary battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a power source for driving EVs and HEVs.

[0066] Although one embodiment of the secondary battery of the present invention has been described above, the present invention is not limited to the configuration described in the above embodiment and may be modified as appropriate based on the claims. For example, the above description has been given using an all-solid-state secondary battery in which the electrolyte contained in the solid electrolyte layer is entirely solid. However, the lithium secondary battery according to this embodiment does not have to be all-solid-state. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferable that the amount be such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolytic solution) does not occur. Note that the liquid electrolyte (electrolytic solution) is a solution in the form of a conventionally known lithium salt dissolved in a conventionally known organic solvent. The liquid electrolyte (electrolytic solution) may further contain additives other than the organic solvent and the lithium salt. These additives may be used alone or in combination. Furthermore, the amount of additive used in the electrolyte solution can be adjusted as appropriate.

[0067] The following embodiments are also included within the scope of the present invention: the secondary battery according to claim 1 having the features of claim 2; the secondary battery according to claim 1 or claim 2 having the features of claim 3; the secondary battery according to any one of claims 1 to 3 having the features of claim 4; the secondary battery according to any one of claims 1 to 4 having the features of claim 5; the secondary battery according to any one of claims 1 to 5 having the features of claim 6; the secondary battery according to any one of claims 1 to 6 having the features of claim 7; the secondary battery according to any one of claims 1 to 7 having the features of claim 8; the secondary battery according to claim 4 having the features of claim 9; the secondary battery according to any one of claims 1 to 9 having the features of claim 10; the secondary battery according to any one of claims 1 to 10 having the features of claim 11; and the secondary battery according to any one of claims 1 to 11 having the features of claim 12.

[0068] 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 instruments and devices used in the glove box were thoroughly dried beforehand.

[0069] <Examples of Preparation of Evaluation Cell> [Example 1] (Preparation of Positive Electrode Active Material Layer) As a constituent material of the positive electrode active material layer, NMC composite oxide (LiNi ０．８ Mn ０．１ Co ０．１ O ２ (NMC811)) and an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ In a glove box with an argon atmosphere having a dew point of −68° C. or less, the positive electrode active material, the solid electrolyte, the conductive additive, and the binder were weighed out to a mass ratio of 79:16:3:2, and then kneaded in an agate mortar to obtain a powder composition (positive electrode mixture).

[0070] The powder composition (positive electrode mixture) obtained above was then formed into a sheet having a thickness of 100 μm using a hand roller. The sheet was punched into a square having a side length of 19 mm to prepare a positive electrode active material layer.

[0071] (Preparation of First Solid Electrolyte Layer) In a glove box with an argon atmosphere having a dew point of −68° C. or less, an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ A solid electrolyte slurry was prepared by mixing 94 parts by mass of styrene-butadiene rubber (SBR) as a binder in mesitylene as a solvent. The obtained solid electrolyte slurry was applied to the surface of a stainless steel foil support using an applicator, dried, and then punched out into a square having a size approximately the same as or slightly larger than the positive electrode active material layer, thereby obtaining a first solid electrolyte layer having a thickness of 1 μm and a binder concentration of 6% by mass.

[0072] (Preparation of Second Solid Electrolyte Layer) In a glove box with an argon atmosphere having a dew point of −68° C. or less, an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５A solid electrolyte slurry was prepared by mixing 95 parts by mass of styrene-butadiene rubber (SBR) as a binder in mesitylene as a solvent. The obtained solid electrolyte slurry was applied to the surface of a stainless steel foil support using an applicator, dried, and then punched out into a square having a size approximately equal to or slightly larger than the positive electrode active material layer, thereby obtaining a second solid electrolyte layer having a thickness of 30 μm and a binder concentration of 5% by mass.

[0073] (Preparation of Intermediate Layer) Silver nanoparticles and carbon black were mixed in a mass ratio of 1:3 to obtain a mixture. Subsequently, a binder solution (a styrene-butadiene rubber (SBR) as a binder dissolved in mesitylene as a solvent) was added and mixed so that the mixture had a mass ratio of 5% relative to the total solid content to obtain a slurry. The slurry was then applied to the surface of a stainless steel foil support using an applicator, dried, and then punched out into a square approximately the same size as or slightly larger than the positive electrode active material layer to obtain a 10 μm thick intermediate layer.

[0074] (Preparation of Evaluation Cell) A positive electrode active material layer was placed on an aluminum foil (square, approximately the same size as or slightly larger than the positive electrode active material layer) as a positive electrode current collector. A first solid electrolyte layer formed on a stainless steel foil surface was then placed on the positive electrode active material layer, with the exposed surface of the solid electrolyte layer facing the positive electrode active material layer, and the solid electrolyte layer was transferred onto the positive electrode active material layer by cold isostatic pressing (CIP). After peeling off the stainless steel foil adjacent to the first solid electrolyte layer, a second solid electrolyte layer formed on the stainless steel foil surface was placed on the transferred first solid electrolyte layer, with the exposed surface of the second solid electrolyte layer facing the first solid electrolyte layer, and the second solid electrolyte layer was transferred onto the first solid electrolyte layer by cold isostatic pressing (CIP). Subsequently, the stainless steel foil adjacent to the second solid electrolyte layer was peeled off, and then an intermediate layer was placed on the transferred second solid electrolyte layer. Then, stainless steel foil serving as a negative electrode current collector was placed on the intermediate layer, and the resulting structure was laminated with a laminate film and pressed by cold isostatic pressing (CIP) to obtain an evaluation cell.

[0075] Example 2 An evaluation cell for Example 2 was obtained in the same manner as Example 1, except that the binder concentration in the first solid electrolyte layer was 5.1 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0076] Example 3 An evaluation cell of Example 3 was obtained in the same manner as Example 1, except that the binder concentration in the first solid electrolyte layer was 6 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0077] Example 4 An evaluation cell of Example 4 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 9.9 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0078] Example 5 An evaluation cell for Example 5 was obtained in the same manner as Example 1, except that the binder concentration in the first solid electrolyte layer was 12 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0079] Example 6 An evaluation cell of Example 6 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 9.9 mass %, the binder concentration in the second solid electrolyte layer was 3 mass %, the thickness of the first solid electrolyte layer was 5 μm, and the thickness of the second solid electrolyte layer was 25 μm.

[0080] Comparative Example 1 An evaluation cell for Comparative Example 1 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 3 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0081] Comparative Example 2 An evaluation cell for Comparative Example 2 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 15 mass % and the binder concentration in the second solid electrolyte layer was 3 mass %.

[0082] Comparative Example 3 An evaluation cell for Comparative Example 3 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 9.9 mass %, the binder concentration in the second solid electrolyte layer was 3 mass %, and the thickness of the first solid electrolyte layer was 15 μm and the thickness of the second solid electrolyte layer was 15 μm.

[0083] Comparative Example 4 An evaluation cell for Comparative Example 4 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 9.9 mass %, the binder concentration in the second solid electrolyte layer was 3 mass %, the thickness of the first solid electrolyte layer was 25 μm, and the thickness of the second solid electrolyte layer was 5 μm.

[0084] Comparative Example 5 An evaluation cell for Comparative Example 5 was obtained in the same manner as in Example 1, except that the binder concentration in the first solid electrolyte layer was 9.9 mass %, the binder concentration in the second solid electrolyte layer was 3 mass %, the thickness of the first solid electrolyte layer was 30 μm, and the thickness of the second solid electrolyte layer was 1 μm.

[0085] [Examples 7 to 11 and Comparative Examples 6 to 7] Evaluation cells of Examples 7 to 11 and Comparative Examples 6 to 7 were obtained in the same manner as in Examples 1 to 5 and Comparative Examples 1 and 2, except that the binder contained in the first solid electrolyte and the second solid electrolyte layer was polyvinylidene fluoride (PVDF).

[0086] <Observation of Adhesion Surface Between First Solid Electrolyte Layer and Positive Electrode Active Material Layer> Each of the evaluation cells prepared above was cut along the lamination direction, and the cross sections of the first solid electrolyte layer and the positive electrode active material layer were observed using an electron probe microanalyzer (EPMA). As a result of the observation, it was found that, at the adhesion surface between the first solid electrolyte layer and the positive electrode active material layer, the binder (SBR or PVDF) present in the surface layer of the first solid electrolyte layer was mixed with the positive electrode active material (NMC811) present in the surface layer of the positive electrode active material layer, and the solid electrolyte (Li ６ P.S. ５ It was confirmed that the carbon black (C1) was bound to the conductive additive (acetylene black) and the binder (SBR).

[0087] <Evaluation of rapid charging characteristics> For each evaluation cell prepared in each of the above examples and comparative examples, a positive electrode lead and a negative electrode lead were connected to the positive electrode current collector and the negative electrode current collector, respectively, and the charge capacity was evaluated according to the following procedure. A charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation) was used for the measurement. The measurement was also carried out in a constant temperature bath set at 60°C, while applying a restraining pressure of 3 MPa in the stacking direction of the evaluation cell using a pressure member.

[0088] First, for each evaluation cell of Examples 1 to 11 and Comparative Examples 1 to 7, constant current (CC) discharge was performed at a current value corresponding to 0.1 C with a lower limit voltage of 0.5 V. Subsequently, in a constant current / constant voltage mode, each cell was charged from 0.5 V to 2.5 V at a constant current of 0.1 C, and the charge capacity at this time was measured. Thereafter, constant current (CC) discharge was performed at a current value corresponding to 2 C with a lower limit voltage of 0.5 V. Subsequently, in a constant current / constant voltage mode, each cell was charged from 0.5 V to 2.5 V at a constant current of 2 C, and the charge capacity at this time was measured. Then, the charge capacity ratio ((charge capacity value when charged at 2 C) / (charge capacity value when charged at 0.1 C)) was calculated, which was the charge capacity when charged at 2 C divided by the charge capacity when charged at 0.1 C, and this was used as an evaluation index for rapid charge characteristics.

[0089]

[0090] As shown in Table 1, the test cells of the Examples had higher charge capacity ratios than the test cells of the Comparative Examples. This indicates that the test cells of the Examples maintained a high rate of charge capacity even when rapidly charged at 2 C. This demonstrates that the secondary battery according to the present invention has improved charge capacity even when rapidly charged.

[0091] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 17a first solid electrolyte layer, 17b second solid electrolyte layer, 19 unit cell layer, 21 power generating element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film.

Claims

1. A positive electrode in which a positive electrode active material layer is disposed on the surface of a positive electrode current collector, A negative electrode in which a negative electrode active material layer is disposed on the surface of a negative electrode current collector, A first solid electrolyte layer and a second solid electrolyte layer each containing a solid electrolyte and a binder, The positive electrode and the negative electrode are oppositely arranged such that the positive electrode active material layer and the negative electrode active material layer sandwich the first solid electrolyte layer and the second solid electrolyte layer, The first solid electrolyte layer is disposed on the positive electrode active material layer side, and the second solid electrolyte layer is disposed on the negative electrode active material layer side, The thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, A secondary battery, wherein the ratio (A / B) of the concentration (A) [% by mass] of the binder to the total solid content of the first solid electrolyte layer and the concentration (B) [% by mass] of the binder to the total solid content of the second solid electrolyte layer is 1.5 ≦ A / B ≦ 3.

5.

2. A positive electrode in which a positive electrode active material layer is disposed on the surface of a positive electrode current collector, A negative electrode in which a negative electrode active material layer is disposed on the surface of a negative electrode current collector, A first solid electrolyte layer and a second solid electrolyte layer each containing a solid electrolyte and a binder, The positive electrode and the negative electrode are oppositely arranged such that the positive electrode active material layer and the negative electrode active material layer sandwich the first solid electrolyte layer and the second solid electrolyte layer, The first solid electrolyte layer is disposed on the positive electrode active material layer side, and the second solid electrolyte layer is disposed on the negative electrode active material layer side, The thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, The ratio (A / B) of the concentration (A) [% by mass] of the binder to the total solid content of the first solid electrolyte layer and the concentration (B) [% by mass] of the binder to the total solid content of the second solid electrolyte layer is 1 < A / B ≦ 4.5, A secondary battery, wherein the first solid electrolyte layer and the second solid electrolyte layer contain solid electrolytes in the same form.

3. A positive electrode in which a positive electrode active material layer is disposed on the surface of a positive electrode current collector, A negative electrode in which a negative electrode active material layer is disposed on the surface of a negative electrode current collector, A first solid electrolyte layer and a second solid electrolyte layer each containing a solid electrolyte and a binder, The positive electrode and the negative electrode are oppositely disposed such that the positive electrode active material layer and the negative electrode active material layer sandwich the first solid electrolyte layer and the second solid electrolyte layer, The first solid electrolyte layer is disposed on the positive electrode active material layer side, and the second solid electrolyte layer is disposed on the negative electrode active material layer side, The thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, The ratio (A / B) of the concentration (A) [% by mass] of the binder to the total solid content of the first solid electrolyte layer and the concentration (B) [% by mass] of the binder to the total solid content of the second solid electrolyte layer is 1 < A / B ≦ 4.5, A secondary battery in which the first solid electrolyte layer and the second solid electrolyte layer contain a solid electrolyte having the same average particle diameter.

4. A positive electrode in which a positive electrode active material layer containing a positive electrode active material that contracts during charging is disposed on the surface of a positive electrode current collector, A negative electrode in which a negative electrode active material layer is disposed on the surface of a negative electrode current collector, A first solid electrolyte layer and a second solid electrolyte layer each containing a solid electrolyte and a binder, The positive electrode and the negative electrode are oppositely disposed such that the positive electrode active material layer and the negative electrode active material layer sandwich the first solid electrolyte layer and the second solid electrolyte layer, The first solid electrolyte layer is disposed on the positive electrode active material layer side, and the second solid electrolyte layer is disposed on the negative electrode active material layer side, The thickness of the first solid electrolyte layer is smaller than the thickness of the second solid electrolyte layer, A secondary battery in which the ratio (A / B) of the concentration (A) [% by mass] of the binder to the total solid content of the first solid electrolyte layer and the concentration (B) [% by mass] of the binder to the total solid content of the second solid electrolyte layer is 1 < A / B ≦ 4.

5.

5. The secondary battery according to claim 2 or 4, wherein the ratio (A / B) is 1.2 ≦ A / B ≦ 4.

0.

6. The secondary battery according to claim 1 or 2, wherein the thickness of the first solid electrolyte layer is 0.1 μm or more and 5 μm or less.

7. The secondary battery according to claim 1 or 2, wherein the positive electrode active material layer contains a positive electrode active material that contracts during charging.

8. The secondary battery according to claim 1 or 2, wherein the binder is selected from the group consisting of polyvinylidene fluoride, styrene-butadiene rubber, acrylic resin, and polytetrafluoroethylene.

9. The secondary battery according to claim 1 or 2, wherein the concentration (A) of the binder with respect to the total solid content of the first solid electrolyte layer is greater than 3% by mass and less than 15% by mass.

10. The secondary battery according to claim 1 or 2, wherein the ratio (b / a) of the thickness (b) of the second solid electrolyte layer to the thickness (a) of the first solid electrolyte layer is 1 < b / a ≦ 50.

11. The solid electrolyte contained in the first solid electrolyte layer and the solid electrolyte contained in the second solid electrolyte layer are the same as each other, The secondary battery according to claim 1 or 4, wherein the binder contained in the first solid electrolyte layer and the binder contained in the second solid electrolyte layer are the same as each other.

12. The secondary battery according to claim 1 or 2, wherein the positive electrode active material contains a composite oxide containing a lithium element and a nickel element.

13. The secondary battery according to claim 1 or 2, which has an intermediate layer containing a carbon material between the negative electrode active material layer and the second solid electrolyte layer.

14. The solid electrolyte contained in the first solid electrolyte layer and the solid electrolyte contained in the second solid electrolyte layer are all solid electrolytes of the argyrodite type (Li ６ PS ５The secondary battery according to claim 1 or 4, wherein X is Cl, Br or I).

15. The secondary battery according to claim 1 or 2, which is an all-solid-state lithium secondary battery.

16. The secondary battery according to claim 2 or 4, wherein the ratio (A / B) is 1.5 ≤ A / B ≤ 3.

5.

17. The secondary battery according to claim 1 or 2, wherein the ratio (A / B) is 1.8 ≤ A / B ≤ 3.0.