Electrode, lithium secondary battery using same, and method for manufacturing electrode

Abstract

The present invention provides a means which is capable of suppressing deterioration of input / output characteristics even under conditions where the cell restraint pressure is low in a lithium secondary battery that uses a solid electrolyte. The present invention relates to an electrode which comprises: a current collector; an active material layer that contains an active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive aid; and a polymer electrolyte layer (A) that is present adjacent to the active material layer, is present on a surface of the active material layer on the current collector side and a surface of the active material layer on the side opposite to the current collector, and contains a polymer electrolyte as a main component.

Description

Electrode, lithium secondary battery using the same, and method for manufacturing the electrode

[0001] This invention relates to an electrode, a lithium secondary battery using the same, and a method for manufacturing the electrode.

[0002] In recent years, research and development on lithium secondary batteries using solid electrolytes has been actively pursued. Solid electrolytes are materials mainly composed of ion conductors capable of conducting lithium ions in a solid state. Therefore, lithium secondary batteries using solid electrolytes have the advantage that, in principle, various problems caused by flammable organic electrolytes, as seen in conventional liquid-based lithium secondary batteries, do not occur.

[0003] On the other hand, lithium secondary batteries using solid electrolytes have the problem that it is difficult to ensure the desired lithium ion conductivity compared to conventional liquid-based lithium secondary batteries, because lithium ion conductivity is exerted through contact between particles via the solid electrolyte. To address this problem, according to the technology described in S. Sen, E. Trevisanello, E. Niemoller, B. -X. Shi, FJ Simon, FH Richter, "The role of polymers in lithium solid-state batteries with inorganic solid electrolytes" J. Mater. Chem. A 2021, 9, 18701-18732, it has been reported that by incorporating a polymer containing an ionic liquid as a binder into the positive electrode active material layer, the lithium ion conductivity at the particle interface inside the positive electrode layer is improved, and battery characteristics such as capacity characteristics are improved.

[0004] However, even with the technology described in the above-mentioned literature, it was found that under conditions of low cell confinement pressure, the contact between the current collector and the active material layer, and between the active material layer and the solid electrolyte layer, is insufficient, resulting in a problem of reduced input / output characteristics.

[0005] Therefore, the object of the present invention is to provide a means that can suppress the deterioration of input / output characteristics in a lithium secondary battery using a solid electrolyte, even under conditions where the cell constraint pressure is low.

[0006] The inventors of the present invention conducted diligent research to solve the above problems. In the process, they discovered that the above problems could be solved by providing a polymer electrolyte layer at the interface between the current collector and the active material layer, and at the interface between the active material layer and the solid electrolyte layer, and by further including a polymer electrolyte in the active material layer, thus completing the present invention.

[0007] In other words, one embodiment of the present invention is an electrode comprising a current collector, an active material layer containing an active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive additive, and a polymer electrolyte layer (A) adjacent to the active material layer, existing on the surface of the active material layer facing the current collector and on the surface of the active material layer opposite to the current collector, and mainly containing a polymer electrolyte.

[0008] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery") which is one embodiment of the present invention. Figure 2 is a schematic cross-sectional view showing the structure of an electrode which is one embodiment of the present invention.

[0009] One embodiment of the present invention is an electrode comprising a current collector, an active material layer containing an active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive additive, and a polymer electrolyte layer (A) adjacent to the active material layer, existing on the surface of the active material layer facing the current collector and on the surface of the active material layer opposite to the current collector, and mainly containing a polymer electrolyte. According to the present invention, in a lithium secondary battery using a solid electrolyte, it is possible to suppress a decrease in input / output characteristics even under conditions of low cell constraint pressure.

[0010] Also provided is a lithium secondary battery comprising a power generation element having a positive electrode having a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing an inorganic solid electrolyte, wherein at least one of the positive electrode and the negative electrode is the electrode described above. In the lithium secondary battery, the electrode described above may be only the positive electrode, only the negative electrode, or both the positive electrode and the negative electrode.

[0011] The lithium secondary battery according to this embodiment will be described below with reference to the attached drawings. The technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0012] Figure 1 is a schematic cross-sectional view showing the overall structure of a stacked (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as "stacked secondary battery"), which is one embodiment of the present invention. By using a stacked design, the battery can be made compact and have a high capacity.

[0013] As shown in FIG. 1, the laminated secondary battery 10a of the present embodiment has a structure in which a flat and substantially rectangular power generation element 21 where charge and discharge reactions actually proceed is sealed inside a laminate film 29 which is a battery exterior material. Here, the power generation element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are laminated. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are laminated. And a negative electrode intermediate layer 14 is disposed adjacent to the surface of the negative electrode active material layer 13 facing the solid electrolyte layer 17. The positive electrode has a structure in which a positive electrode active material layer 15 is disposed on the surface of the positive electrode current collector 11". And the negative electrode intermediate layer 14 and the positive electrode active material layer 15 face each other through the solid electrolyte layer 17, and the negative electrode, the solid electrolyte layer, and the positive electrode are laminated in this order. Thereby, the adjacent positive electrode, solid electrolyte layer, and negative electrode constitute one single battery layer 19. Therefore, it can also be said that the laminated secondary battery 10a shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are laminated and electrically connected in parallel. Negative electrode current collectors 25 and positive electrode current collectors 27 that are electrically connected to the respective electrodes (negative electrode and positive electrode) are attached to the negative electrode current collector 11' and the positive electrode current collector 11" respectively, and have a structure in which they are led out to the outside of the laminate film 29 so as to be sandwiched between the ends of the laminate film 29. A restraining pressure is applied to the power generation element 21 in the lamination direction by a pressing member (not shown) in the laminated secondary battery 10a. Therefore, the volume of the power generation element 21 is kept constant.

[0014] Hereinafter, the main constituent members of the lithium secondary battery according to the present embodiment will be described. In this specification, "X to Y" indicating a range means "X or more and Y or less".

[0015] <Electrode>FIG. 2 is a cross-sectional view schematically showing the structure of an electrode according to an embodiment of the present invention. The electrode includes a current collector (the positive electrode current collector 11" or the negative electrode current collector 11') and an active material layer (the positive electrode active material layer 15 or the negative electrode active material layer 13) formed on the current collector. Further, polymer electrolyte layers (A) 30, 30' are present adjacent to the positive electrode active material layer 15 or the negative electrode active material layer 13, and are present on the surface on the side of the positive electrode current collector 11" or the negative electrode current collector 11' (the surface contacting the positive electrode current collector or the negative electrode current collector) and the surface on the opposite side thereof. Furthermore, a polymer electrolyte layer (B) 31 is disposed at at least a part of the outer periphery of the active material layer when the power generation element is viewed in plan. The electrode can be either a positive electrode or a negative electrode, but is preferably a positive electrode.

[0016] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has a function of mediating the movement of electrons from the active material layer (negative electrode active material layer, positive electrode active material layer). There is no particular limitation on the material constituting the current collector. As the constituent material of the current collector, for example, metals such as aluminum, nickel, iron, stainless steel, titanium, copper, or a conductive resin can be adopted. There is no particular limitation on the thickness of the current collector either, but as an example, it is 10 to 100 μm.

[0017] [Polymer Electrolyte Layer (A)] In the electrode, the polymer electrolyte layer (A) is present adjacent to the active material layer, and is present on the surface of the active material layer on the side of the current collector and the surface of the active material layer on the opposite side of the current collector. In the present specification, the polymer electrolyte layers present on the surface of the active material layer on the side of the current collector and the surface of the active material layer on the opposite side of the current collector are collectively referred to as the "polymer electrolyte layer (A)". Further, when only the polymer electrolyte layer present on the surface on the side of the current collector is represented, it is referred to as the "polymer electrolyte layer (A-1)". On the other hand, when only the polymer electrolyte layer present on the surface on the opposite side of the current collector is represented, it is referred to as the "polymer electrolyte layer (A-2)". Furthermore, the polymer electrolyte layer disposed at at least a part of the outer periphery of the active material layer when the power generation element is viewed in plan is referred to as the "polymer electrolyte layer (B)". Therefore, the sequences themselves of "(A)" and "(B)", and "(A-1)" and "(A-2)" have no meaning, and these terms are merely expressions for distinguishing the sites where the polymer electrolyte layers are present.

[0018] The polymer electrolyte layer (A) contains a polymer electrolyte as its main component (in an amount exceeding 50% by mass relative to the total solid content of the polymer electrolyte layer). The polymer electrolyte can be one of conventionally known types and generally comprises an ionic conductive polymer compound and an ionic salt such as a lithium salt. The polymer compound may have dissociation groups in its structural units. The polymer electrolyte may also contain a composite of the polymer compound and the ionic salt. In particular, from the viewpoint of reducing resistance increase, the polymer electrolyte is preferably a composite of the polymer compound and a lithium salt. The polymer electrolyte having dissociation groups in its repeating polymer units is not particularly limited, and conventionally known compounds can be appropriately selected.

[0019] (Polymer Compound) The polymer compound is not particularly limited, and conventionally known polymer compounds can be appropriately selected, but those with excellent binding strength and compatibility with lithium salts are preferably selected. Examples of polymer compounds include those containing one or more structures selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyethylene oxide (PEO), polyethylene carbonate, polypropylene carbonate, polyacrylonitrile (PAN), and polymethyl methacrylate (PMMA). Furthermore, it is preferable that the polymer compound be one or more polymer compounds selected from the above group. Among these, from the viewpoint of binding strength and compatibility with lithium salts, polymer compounds containing fluorine atoms are preferred, and vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is particularly preferred. PVDF-HFP is not particularly limited as long as it is a copolymer containing structural units derived from vinylidene fluoride and hexafluoropropylene, and may optionally further contain structural units derived from a third comonomer, but is preferably not included. The proportion of structural units derived from hexafluoropropylene in PVDF-HFP is not particularly limited, but is, for example, 1 to 50 mol% of the total structural units of PVDF-HFP.

[0020] (Lithium Salt) A lithium salt is a salt composed of lithium ions and anions, and those with excellent compatibility with polymer compounds are preferably selected. Examples of lithium salts include, for example, those represented by Chemical Formula 2: ((C ｍ F ２ｍ＋１ )SO ２ )((C ｎ F ２ｎ＋１ )SO ２ )NLi (in Chemical Formula 2, m and n are each independently one of the integers from 0 to 4), fluorine-containing sulfonylimide lithium salts represented by the following Chemical Formula 3, fluorine-containing sulfonylimide lithium salts represented by the following Chemical Formula 4, lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), LiClO ４ (lithium perchlorate), lithium hexafluoroarsenate (LiAsF ６ ), lithium trifluoroacetate (CF ３ COOLi), lithium bis(oxalato)borate (LiB(C ２ O ４ ) ２ ), etc. Among them, it is preferably a fluorine-containing sulfonylimide lithium salt represented by the above Chemical Formula 2, and it is more preferably at least one of lithium bis(fluorosulfonyl)imide (LiN(SO ２ F) ２、 , also referred to as "LiFSI" in this specification) and lithium bis(trifluoromethanesulfonyl)imide (LiN(SO ２ CF ３ ) ２ , also referred to as "LiTFSI" in this specification).

[0021]

[0022] The mechanism by which a polymer electrolyte layer (A) can be provided at the interface between the current collector and the active material layer, and at the interface between the active material layer and the solid electrolyte layer, and further by including a polymer electrolyte in the active material layer, thereby suppressing the deterioration of input / output characteristics, is not fully understood, but the following mechanism is hypothesized. That is, by providing a layer containing a polymer electrolyte with strong binding force at the interface between the current collector and the active material layer, and at the interface between the active material layer and the solid electrolyte layer, contact between the current collector and the active material layer, and contact between the active material layer and the solid electrolyte layer can be maintained. In addition, since the polymer electrolyte layer (A) has sufficient lithium ion conductivity, the increase in resistance at the above interface can be suppressed. Furthermore, by including a polymer electrolyte in the active material layer as well, sufficient lithium ion conductivity can be ensured while enhancing the contact between the active material and the inorganic solid electrolyte in the active material layer, thereby reducing resistance and suppressing the deterioration of input / output characteristics. It should be noted that the above mechanism is based on speculation, and its accuracy does not affect the technical scope of the present invention.

[0023] The content of the polymer compound in the composite of the polymer compound and lithium salt is, for example, 50% to 90% by mass, preferably 60% to 80% by mass, based on the total mass of the composite. The content of the lithium salt in the composite of the polymer compound and lithium salt is, for example, 10% to 50% by mass, preferably 20% to 40% by mass, based on the total mass of the composite.

[0024] Furthermore, the polymer electrolyte content (total content of polymer compounds and lithium salts) in the polymer electrolyte layer (A) is more than 50% by mass of the total mass of the polymer electrolyte layer (A), for example, 70% to 100% by mass, preferably 90% to 100% by mass, and particularly preferably 100% by mass. That is, in a preferred embodiment, the polymer electrolyte layer (A) consists only of polymer electrolytes.

[0025] In one embodiment of the present invention, the polymer electrolyte layer (A-1) located on the current collector side of the active material layer and the polymer electrolyte layer (A-2) located on the side of the active material layer opposite to the current collector side are composed of the same material.

[0026] The thickness of the polymer electrolyte layer (A-1) on the current collector side of the active material layer and the thickness of the polymer electrolyte layer (A-2) on the side of the active material layer opposite to the current collector side may be the same or different. If the thicknesses of the polymer electrolyte layer (A-1) and the polymer electrolyte layer (A-2) are different, it is preferable that the polymer electrolyte layer (A-1) is smaller than the polymer electrolyte layer (A-2). With the above structure, the increase in resistance due to polymer components is reduced while exhibiting excellent bonding strength, thereby further improving the input / output characteristics.

[0027] The thickness of the polymer electrolyte layer (A-1) is, for example, 0.2 μm to 10 μm, preferably 0.5 μm to 7.0 μm, more preferably 0.7 μm to 5.0 μm, and particularly preferably 1 μm to 3.0 μm. The thickness of the polymer electrolyte layer (A-2) is, for example, 1 μm to 15 μm, preferably 1.2 μm to 7.0 μm, more preferably 1.5 μm to 5.0 μm, and particularly preferably 2.0 μm to 4.0 μm.

[0028] The total thickness of the polymer electrolyte layer (A) (the sum of the thickness of polymer electrolyte layer (A-1) and polymer electrolyte layer (A-2)) is, for example, 2 μm to 15 μm, preferably 2.5 μm to 10 μm, and more preferably 3 μm to 7 μm. When within the above range, excellent bonding strength is observed, and the increase in resistance can be further reduced.

[0029] [Polymer electrolyte layer (B)] The electrode may have a polymer electrolyte layer (B) arranged on at least a portion of the outer circumference of the active material layer when the power generation element is viewed in plan. The presence of the polymer electrolyte layer (B) can suppress short circuits that may occur from the edges. It is preferable that the polymer electrolyte layer (B) extends over the entire outer circumference. In one embodiment of the present invention, the polymer electrolyte layer (B) and the polymer electrolyte layer (A) (polymer electrolyte layer (A-1) and polymer electrolyte layer (A-2)) are composed of the same composition. The thickness of the polymer electrolyte layer (B) is not particularly limited, but is for example 0.2 μm to 15 μm, and preferably 1.5 μm to 10 μm.

[0030] [Positive Electrode Active Material Layer] When the electrode in this embodiment is the positive electrode, the positive electrode active material layer must include a positive electrode active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive additive. The type of positive electrode active material included in the positive electrode active material layer is not particularly limited, but LiCoO ２ LiMnO ２ LiNiO ２ LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt type 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 ２ MnSiO ４ Examples of Si-containing active materials include the above. Other oxide active materials include, for example, Li ４ Ti ５ O １２ These include Li(Ni-Mn-Co)O ２ Furthermore, materials in which some of these transition metals are substituted with other elements (hereinafter also simply referred to as "NMC composite oxides") are preferably used as positive electrode active materials. Another preferred embodiment is the use of sulfur-based positive electrode active materials. Examples of sulfur-based positive electrode active materials include particles of organic sulfur compounds or inorganic sulfur compounds, and any material that can release lithium ions during charging and absorb lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur is acceptable. The content of positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably 30 to 99% by mass, and particularly preferably 70 to 90% by mass.

[0031] The positive electrode active material layer further comprises an inorganic solid electrolyte. The inorganic solid electrolyte used in the positive electrode active material layer is not particularly limited, and any known in the art can be used as appropriate, but examples include sulfide solid electrolytes and oxide solid electrolytes. Among these, a sulfide solid electrolyte is preferred because it exhibits excellent lithium ion conductivity, more preferably a sulfide solid electrolyte containing Li and M elements, wherein the M element is 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 Li and P elements. As an example, LPS(Li ２ S-P ２ S ５ ), Li ６ PS ５ X (where X is Cl, Br, or I), Li ７ P ３ S １１ Li ３．２ P ０．９６ S and Li ３ PS ４ Examples of sulfide solid electrolytes include the following. These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity. The ionic conductivity (e.g., Li ion conductivity) of sulfide solid electrolytes at room temperature (25°C) is, for example, 1 × 10⁻⁶. －５ It is preferable that the S / cm is greater than or equal to 1 × 10 －４ It is more preferable that the ionic conductivity is S / cm or higher. The ionic conductivity of the solid electrolyte can be measured by the AC impedance method. Examples of the shape of the inorganic solid electrolyte include spherical, ellipsoidal, and other particulate forms. When the inorganic solid electrolyte is particulate, its average particle diameter (D50) is not particularly limited, but is preferably 0.01 μm to 40 μm, and more preferably 0.1 μm to 10 μm. There are no particular restrictions on the content of the inorganic solid electrolyte in the positive electrode active material layer, but is, for example, 1 to 70% by mass, and preferably 10 to 40% by mass.

[0032] The positive electrode active material layer further contains a binder. In this specification, the term "binder" is distinguished from the polymer compounds that are components of the polymer electrolyte and means a material that does not have ionic conductivity. Examples of binders used in the positive electrode active material layer include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethylcellulose. In particular, when the process of manufacturing the electrode includes impregnation with a polymer electrolyte solution to incorporate the polymer electrolyte into the positive electrode active material layer, a fibrous binder is preferred, and polytetrafluoroethylene (PTFE) is particularly preferred. The binder content in the positive electrode active material layer is not particularly limited, but is, for example, 1 to 10% by mass, and preferably 1 to 5% by mass, relative to the total mass of the positive electrode active material layer. A positive electrode active material layer with sufficient strength can be formed if the binder content is 1% by mass or more. If the binder content is 10% by mass or less, sufficient lithium-ion conductivity can be ensured.

[0033] The conductive additive used in the positive electrode active material layer is not particularly limited, and for example, carbon such as carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.), carbon nanotubes, and carbon nanofibers may be used. The content of the conductive additive in the positive electrode active material layer is not particularly limited, but for example, it is 1 to 30% by mass. These conductive additives may be used individually or in combination of two or more. The content of the conductive additive in the positive electrode active material layer is, for example, 1 to 10% by mass relative to the total mass of the positive electrode active material layer.

[0034] The polymer electrolyte contained in the positive electrode active material layer can be the same polymer electrolyte described in the section on polymer electrolyte layer (A). In one embodiment, the polymer electrolyte contained in the positive electrode active material layer is the same as that contained in polymer electrolyte layer (A).

[0035] The content of the polymer electrolyte contained in the positive electrode active material layer may have a gradient in the stacking direction of the positive electrode active material layer and / or in a direction perpendicular to the stacking direction of the positive electrode active material layer. When there is a gradient in the content of the polymer electrolyte in the stacking direction of the positive electrode active material layer, it is preferable that the content of the polymer electrolyte present on the surface of the positive electrode active material layer is higher than the content of the polymer electrolyte present in the central part of the positive electrode active material layer. Furthermore, when there is a gradient in the content of the polymer electrolyte perpendicular to the stacking direction of the positive electrode active material layer, it is preferable that the content of the polymer electrolyte present on the surface of the active material layer is higher than the content of the polymer electrolyte present in the central part of the active material layer. With such a structure, the bonding force between components within the positive electrode active material layer is improved, and at the same time, the adhesive force at the battery interface is improved, allowing the effects of the present invention to be exhibited even more effectively.

[0036] The thickness of the positive electrode active material layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 300 μm.

[0037] The polymer electrolyte content (solid content) in the laminate of the positive electrode active material layer and the polymer electrolyte layer is preferably 1 to 10% by mass, more preferably 1 to 5% by mass, and even more preferably 2 to 4% by mass, relative to the total mass of the laminate. Within this range, the effects of the present invention can be obtained even more significantly.

[0038] [Negative Electrode Active Material Layer] When the electrode in this embodiment is the negative electrode, the negative electrode active material layer essentially includes a negative electrode active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive additive. Examples of negative electrode active materials include carbon materials, metal oxides, and metal active materials. In addition, an active material containing lithium may be used as the negative electrode active material. Such a negative electrode active material is not particularly limited as long as it contains lithium, and examples include lithium metal and lithium-containing alloys. Examples of lithium-containing alloys include alloys of Li and at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. The negative electrode active material preferably contains lithium metal or a lithium-containing alloy, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably lithium metal or a lithium-containing alloy.

[0039] When the electrode of the present invention is the positive electrode, the negative electrode does not have to be the electrode of the present invention. In one embodiment, the negative electrode may be a negative electrode using lithium metal or a lithium-containing alloy as the negative electrode active material. In this case, the lithium secondary battery is preferably a so-called lithium deposition type, in which lithium metal as the negative electrode active material is deposited on the negative electrode current collector during the charging process. In this case, the layer made of lithium metal deposited during the charging process becomes the negative electrode active material layer, so the thickness of the negative electrode active material layer increases as the charging process progresses and decreases as the discharge process progresses. The negative electrode active material layer does not have to be present during complete discharge, but in some cases, a negative electrode active material layer made of a certain amount of lithium metal may be placed during complete discharge. Furthermore, the thickness of the negative electrode active material layer (lithium metal layer) during complete charge is not particularly limited, but it is usually 0.1 to 1000 μm.

[0040] The components other than the negative electrode active material contained in the negative electrode active material layer are as described in the section on the positive electrode active material layer. The thickness of the negative electrode active material layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 300 μm.

[0041] <Negative Electrode Intermediate Layer> When the lithium secondary battery according to this embodiment is of the lithium deposition type described above, the negative electrode intermediate layer may be arranged adjacent to the negative electrode current collector side surface of the solid electrolyte layer. Preferably, the negative electrode intermediate layer is conductive as a whole. The negative electrode intermediate layer may also contain a lithium-reactive material, for example, a carbon material. When a carbon material is included in the negative electrode intermediate layer, the generation and growth of dendrites can be suppressed particularly effectively.

[0042] Specific examples of carbon materials include carbon black (specifically, acetylene black, Ketjenblack®, furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNTs), graphite, and hard carbon. The carbon material content is, for example, 40% to 99% by mass, preferably 50% to 80% by mass, relative to the total mass of the negative electrode intermediate layer. When the carbon material content is within the above range, the generation and growth of dendrites can be suppressed.

[0043] The negative electrode intermediate layer may contain a binder as needed. Examples of binders include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethylcellulose. The binder content is preferably in the range of, for example, 1 to 20% by mass relative to the total mass of the negative electrode intermediate layer.

[0044] The negative electrode intermediate layer may contain additional metallic material. Examples of metallic material include In, Al, Si, Sn, Mg, Au, Ag, and Zn. The metallic material content is, for example, 0 to 35% by mass relative to the total mass of the negative electrode intermediate layer.

[0045] <Solid Electrolyte Layer> The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains an inorganic solid electrolyte (usually as the main component). The specific form of the inorganic solid electrolyte contained in the solid electrolyte layer can be the same as the form described in the positive electrode active material layer section. Among these, sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity. The inorganic solid electrolyte content is preferably 90 to 100% by mass.

[0046] The solid electrolyte layer may further contain a binder in addition to the inorganic solid electrolyte. The binder is not particularly limited, and for example, the binder described above for the negative electrode intermediate layer can be used in a similar manner. The binder content in the solid electrolyte layer is, for example, 1 to 10% by mass.

[0047] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, and preferably 10 to 100 μm.

[0048] Although one embodiment of the electrode of the present invention and a lithium secondary battery using the same has been described above, the present invention is not limited to the configuration described in the above-mentioned embodiment and can be modified as appropriate based on the description of the claims.

[0049] Furthermore, the lithium secondary battery according to this embodiment may be all-solid-state or not. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There are no particular restrictions on the amount of liquid electrolyte (electrolyte) that can be contained in the solid electrolyte layer, but it is preferable that the amount is such that the shape of the solid electrolyte layer formed by the solid electrolyte is maintained and leakage of the liquid electrolyte (electrolyte) does not occur.

[0050] <Method for Manufacturing an Electrode> Next, a method for manufacturing an electrode according to another embodiment of the present invention will be described. The method for manufacturing an electrode according to this embodiment includes: mixing an active material, an inorganic solid electrolyte, a conductive additive, and a binder to obtain a mixture; forming an active material layer precursor from the mixture; adding a polymer electrolyte solution containing a polymer electrolyte and a solvent to the active material layer precursor; and removing the solvent and drying to form a laminate consisting of an active material layer and a polymer electrolyte layer (A). According to this manufacturing method, a lithium secondary battery according to the above-described embodiment of the present invention can be manufactured. However, the technical scope of a lithium secondary battery according to the embodiment of the present invention is not limited to those manufactured by this manufacturing method.

[0051] [Preparation of Active Material Layer Precursor] (Mixing Step) The mixing step is a process of mixing components including the active material, inorganic solid electrolyte, conductive additive, and binder to obtain a mixture. In the mixing step, the components to be mixed may or may not include a solvent in addition to the active material, inorganic solid electrolyte, conductive additive, and binder, but it is preferable not to include a solvent from the viewpoint of effectively suppressing the degradation of the inorganic solid electrolyte. In other words, dry mixing is preferable. Details of the components contained in the mixture are as described in the positive electrode active material layer section and the negative electrode active material layer section. The active material among the components contained in the mixture is either the positive electrode active material or the negative electrode active material.

[0052] The method of addition and mixing is not particularly limited, and conventionally known methods may be used as appropriate. For example, a predetermined amount of each component to be included is weighed, and they are added to a stirring container sequentially or simultaneously, in any order, and mixed by manual or automatic mixing means. Alternatively, if the mixture contains a binder, the components other than the binder may be weighed, added, and mixed first, then the binder may be weighed and added to the mixture and mixed. If the binder contains PTFE, it is preferable to weigh, add, and mix the components other than PTFE first, then weigh the PTFE and add it to the mixture, and mix until the PTFE fibrillates and becomes fibrous by kneading.

[0053] (Active material layer precursor formation step) The active material layer precursor formation step is a step in which an active material layer precursor is formed from the mixture obtained in the mixing step described above. If the mixture does not contain any solvents, the formation method may be, for example, by placing the mixture in a press and forming it by pressure molding or rolling. Examples of presses include roll presses, but are not limited to these, and conventionally known presses may be appropriately selected. In the active material layer precursor formation step, it is also preferable not to use any solvents.

[0054] [Preparation of a laminate consisting of an active material layer and a polymer electrolyte layer (A)] (Polymer electrolyte addition step) The polymer electrolyte addition step is a step of adding a polymer electrolyte solution to the active material layer precursor. The method of addition is not particularly limited as long as it can contain or coat the polymer electrolyte solution inside the voids present in the active material layer precursor and on the surface of the active material layer precursor. As an example, the polymer electrolyte addition step includes a step of impregnating the active material layer precursor with the polymer electrolyte solution. That is, a container containing the polymer electrolyte solution is prepared, and the active material layer precursor is placed into the container to impregnate the active material layer precursor with the polymer electrolyte solution. Furthermore, the above impregnation may be performed by reduced pressure impregnation (vacuum impregnation). That is, the above impregnation may be performed under reduced pressure conditions lower than 1 atmosphere.

[0055] When a polymer electrolyte is added to the active material layer precursor by impregnation, the polymer electrolyte can be efficiently incorporated into the voids present in the active material layer precursor. Furthermore, a laminate consisting of the resulting active material layer and polymer electrolyte layer (A) can be obtained that has a gradient in the polymer electrolyte content. The laminate may have a gradient in the stacking direction and / or in the direction perpendicular to the stacking direction, and in each direction, the polymer electrolyte content present on the surface of the active material layer may be higher than the polymer electrolyte content present in the central part of the active material layer.

[0056] The polymer electrolyte solution used in the polymer electrolyte addition step comprises a polymer electrolyte and a solvent. The polymer electrolyte can be one of those listed in the section on polymer electrolyte layer (A). Examples of solvents are not particularly limited as long as they can dissolve or disperse the polymer electrolyte, but examples include acetonitrile, propionitrile, tetrahydrofuran, and tetrahydropyran. Among these, acetonitrile is preferred from the viewpoint of polymer electrolyte solubility.

[0057] Furthermore, in one embodiment, the amount of polymer electrolyte contained in the active material layer and the thickness of the polymer electrolyte layer formed on the surface of the active material can be controlled by appropriately selecting the concentration of the polymer electrolyte solution used. That is, the higher the concentration of the polymer electrolyte solution, the less likely the polymer electrolyte solution is to penetrate the active material layer due to the viscosity of the solution, so the amount of polymer electrolyte contained in the active material layer decreases relatively, and the thickness of the polymer electrolyte layer formed on the surface increases. On the other hand, the lower the concentration of the polymer electrolyte solution, the lower the viscosity of the solution, so the more likely the polymer electrolyte is to penetrate the active material layer, so the amount of polymer electrolyte contained in the active material layer increases relatively, and the thickness of the polymer electrolyte layer formed on the surface decreases. The concentration of the polymer compound in the polymer electrolyte solution is, for example, 1% to 10% by mass, preferably 2% to 7% by mass.

[0058] (Drying process) The drying process is a process in which the solvent is removed from the active material layer precursor after the polymer electrolyte addition process described above to form a laminate consisting of an active material layer and a polymer electrolyte layer (A). The resulting laminate has a structure in which the polymer electrolyte layer is formed on all or some of the surfaces of the active material layer. That is, when used as a lithium secondary battery, a polymer electrolyte layer (A) may be formed which is adjacent to the active material layer and which is present on the surface of the active material layer on the current collector side and the surface on the opposite side of the current collector, as well as a polymer electrolyte layer (B) which is arranged on at least a part of the outer circumference of the active material layer when the power generation element is viewed in plan.

[0059] The method for removing the solvent is not particularly limited and can be carried out as appropriate with reference to conventionally known knowledge. As an example, the solvent can be removed by placing the active material layer precursor before drying on a substrate and leaving it standing for a certain period of time under high temperature and reduced pressure conditions. The material of the substrate is not particularly limited and can be, for example, PTFE. The standing temperature is, for example, 25°C to 100°C, preferably 40°C to 80°C. The standing pressure is, for example, 0.001 atmospheres to 1 atmosphere, preferably 0.005 atmospheres to 0.1 atmospheres. The standing time is, for example, 10 minutes to 3 days, preferably 3 hours to 24 hours.

[0060] When a drying process is performed on a substrate, the thicknesses of the multiple polymer electrolyte layers in the resulting laminate may differ. Specifically, due to gravity during drying, the polymer electrolyte layer formed on the substrate-side surface (i.e., bottom surface) of the active material layer may be thinner than the polymer electrolyte layer formed on the opposite side of the active material layer from the substrate (i.e., top surface).

[0061] [Electrode Fabrication] (Current Collector Placement Step) The manufacturing method of the lithium secondary battery according to this embodiment may further include a current collector placement step. The current collector placement step is a step of placing the laminate obtained above onto a current collector to obtain an electrode. In particular, if the drying step is performed on a substrate, it is preferable to peel the laminate from the substrate and place it on the current collector so that the surface of the laminate that was in contact with the substrate is in contact with the current collector. By placing it as described above, an electrode is obtained in which the polymer electrolyte layer (A-1) on the side facing the current collector is thinner than the polymer electrolyte layer (A-2) on the side opposite to the current collector. At least one of the positive electrode and the negative electrode is the electrode obtained in the above step, and preferably the positive electrode is the electrode obtained in the above step.

[0062] In the electrode manufacturing method according to this embodiment, in the production of the active material layer, before incorporating the polymer electrolyte, a step is taken to form an active material layer precursor by mixing only the components constituting the active material layer excluding the polymer electrolyte and subjecting them to a molding process. Then, a step is taken to add the polymer electrolyte solution, which is a characteristic feature. By producing the active material layer in the above step, the voids present in the active material layer precursor are filled with the polymer electrolyte, and lithium ion conductivity can be improved while maintaining adhesion between solids in the active material layer (for example, between particles such as the active material and inorganic solid electrolyte), thereby improving the input / output characteristics of the battery. Furthermore, by adding the polymer electrolyte solution to the molded active material layer precursor, the surface of the active material layer can be coated with the polymer electrolyte. Therefore, the bonding force between the active material layer and the current collector and solid electrolyte layer is strengthened, the increase in resistance is suppressed, and it is thought that the deterioration of the battery's input / output characteristics can be suppressed even under conditions of low cell constraint pressure. It should be noted that the above mechanism is based on speculation, and its accuracy does not affect the technical scope of the present invention.

[0063] According to one embodiment of the present invention, a method for manufacturing a lithium secondary battery is also provided, which includes manufacturing electrodes by the above manufacturing method. A lithium secondary battery including electrodes manufactured by the above manufacturing method is also provided.

[0064] While embodiments of the present invention have been described in detail, these are descriptive and illustrative, and not limiting, and it is clear that the scope of the present invention should be interpreted by the appended claims.

[0065] Furthermore, the following items are also included in the scope of the present invention: an electrode according to claim 1 having the features of claim 2; an electrode according to claim 1 or 2 having the features of claim 3; an electrode according to any one of claims 1 to 3 having the features of claim 4; an electrode according to any one of claims 1 to 4 having the features of claim 5; an electrode according to any one of claims 1 to 5 having the features of claim 6; an electrode according to any one of claims 1 to 6 having the features of claim 7; an electrode according to any one of claims 1 to 7 having the features of claim 8; an electrode according to claims 1 to 8 having the features of claim 9; a lithium secondary battery according to claim 10 comprising the electrodes according to claims 1 to 9; a manufacturing method according to claim 11 having the features of claim 12; a manufacturing method according to claim 11 or 12 having the features of claim 13; a manufacturing method according to any one of claims 11 to 13 having the features of claim 14; a manufacturing method according to any one of claims 11 to 14 having the features of claim 15; a manufacturing method according to any one of claims 11 to 15 having the features of claim 16; a manufacturing method according to any one of claims 11 to 16 having the features of claim 17; a manufacturing method according to any one of claims 11 to 17 having the features of claim 18.

[0066] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following, the operations were carried out in a glove box with an argon atmosphere with a dew point of -68°C or lower. Furthermore, the instruments and equipment used in the glove box were thoroughly dried beforehand.

[0067] <Example of evaluation cell fabrication> [Comparative example 1] (Fabrication of positive electrode active material layer) As the constituent material of the positive electrode active material layer, NMC composite oxide (LiNi) is used as the positive electrode active material. ０．８ Mn ０．１ Co ０．１ O ２ , average particle size (D50): 1 μm, and argyrodite-type sulfide solid electrolyte (Li) which is an inorganic solid electrolyte. ６ PS ５Cl (average particle size (D50): 0.2 μm), carbon nanofiber (CNF) (manufactured by Showa Denko K.K., VGCF®, aspect ratio: 60, average fiber diameter: 150 nm, average fiber length: 9 μm), a fibrous conductive additive, and polytetrafluoroethylene (PTFE), a binder capable of fibrillation, were prepared. In a glove box with an argon atmosphere and a dew point of -68°C or lower, predetermined amounts of the cathode active material, inorganic solid electrolyte, and conductive additive prepared above were kneaded in an agate mortar to obtain a homogeneous mixture. Next, a predetermined amount of PTFE was added to the mixture and kneaded further in an agate mortar to obtain a solvent-free dry powder composition (costoichiometric mixture). The appearance of the mixture obtained in this way resembled udon noodle dough. The mixing ratio of each component in the mixture (mass ratio of positive electrode active material: inorganic solid electrolyte: fibrous conductive additive: binder) was set to 81.3:14.4:2.9:1.4.

[0068] After confirming that the PTFE had fibrillated and become fibrous through kneading, the obtained powder composition (mixture for cathode formation) was supplied to the powder inlet set in the roll press machine. The powder composition was then rolled using the roll press machine (conditions are shown below) to form it into a sheet.

[0069] Next, the sheet was punched out into a 19 mm square rectangular shape so that one pair of opposite sides were parallel to the direction of rolling by the roll press, thereby obtaining a positive electrode active material layer with a thickness of 165 μm. The weight of the obtained positive electrode active material layer was 30 mg.

[0070] (Preparation of the solid electrolyte layer) In a glove box with an argon atmosphere and a dew point of -68°C or lower, an argyrodite-type sulfide solid electrolyte (Li) is prepared as an inorganic solid electrolyte. ６ PS ５A solid electrolyte layer slurry was prepared by mixing 95 parts by mass of Cl with a binder solution (5 parts by mass of styrene-butadiene rubber (SBR) as a binder dissolved in mesitylene as a solvent). The obtained solid electrolyte layer slurry was coated onto the surface of a stainless steel foil support using an applicator, dried, and then punched out into a 25 mm square rectangular shape to obtain a solid electrolyte layer with a thickness of 40 μm.

[0071] (Preparation of the negative electrode intermediate layer) Silver nanoparticles and carbon black nanoparticles were weighed in a mass ratio of 1:3 and mixed. Five parts by mass of the resulting mixture was added to a binder solution (0.5 parts by mass of styrene-butadiene rubber (SBR) as a binder dissolved in mesitylene as a solvent) and mixed to prepare a negative electrode intermediate layer slurry. The obtained negative electrode intermediate layer slurry was coated onto the surface of a stainless steel foil used as a negative electrode current collector using an applicator, dried, and then punched out into a rectangular shape with a diameter of 21 mm to obtain a negative electrode intermediate layer with a thickness of 10 μm.

[0072] (Preparation of evaluation cell) The positive electrode active material layer prepared above was placed on top of an aluminum foil (19 mm square rectangular shape) used as the positive electrode current collector. Then, the solid electrolyte layer formed on the stainless steel foil surface prepared above was transferred to the exposed surface of the positive electrode active material layer by cold isostatic pressing (CIP) so that the exposed surface of the solid electrolyte layer faced the positive electrode active material layer. After that, the stainless steel foil was peeled off, and the negative electrode intermediate layer formed on the stainless steel foil surface prepared above was placed on the exposed surface of the solid electrolyte layer so that the exposed surface of the negative electrode intermediate layer faced the solid electrolyte layer, and pressure was applied by cold isostatic pressing (CIP) to obtain an evaluation cell (lithium deposition type all-solid-state lithium secondary battery).

[0073] [Example 1] (Preparation of polymer electrolyte solution) 0.38 g of PVDF-HFP (Arkema, KYNAR FLEX®) and 0.12 g of lithium bis(trifluoromethanesulfonyl)imide (Kishida Chemical, LiTFSI) were weighed out. These were added to 49.5 g of acetonitrile. A polymer electrolyte solution was prepared by stirring this at room temperature overnight (polymer compound concentration (concentration of PVDF-HFP relative to the total mass of the solution, the same applies hereinafter): 1.7% by mass).

[0074] (Preparation of a laminate of polymer electrolyte layer (A) and positive electrode active material layer) The positive electrode active material layer (19 mm square, 30 mg) obtained in Comparative Example 1 (Preparation of positive electrode active material layer) above was used as the positive electrode active material layer precursor. The positive electrode active material layer precursor was placed in the pass box of a glove box (NEXUS II, manufactured by VAC), a polymer electrolyte solution was added, and vacuum impregnation was performed at a pressure of less than 1 kPa at 25°C for 1 minute. After that, the positive electrode active material layer precursor that had been vacuum impregnated with the polymer electrolyte solution was removed and placed on a drying substrate (PTFE Petri dish), and vacuum dried at 60°C for 24 hours. After that, it was peeled off from the drying substrate (PTFE Petri dish) to prepare a laminate of polymer electrolyte layer (A) and positive electrode active material layer.

[0075] The preparation of the solid electrolyte layer and the negative electrode intermediate layer was carried out using the same method as in Comparative Example 1.

[0076] (Preparation of evaluation cell) The obtained laminate was placed on the positive electrode current collector such that the surface that was in contact with the substrate during vacuum drying was in contact with the aluminum foil, which serves as the positive electrode current collector. Then, the solid electrolyte layer formed on the stainless steel foil surface prepared above was transferred to the exposed surface of this laminate by cold isostatic pressing (CIP) so that the exposed surface of the solid electrolyte layer faced the laminate. After that, the stainless steel foil was peeled off, and the negative electrode intermediate layer formed on the stainless steel foil surface prepared above was placed on the exposed surface of the solid electrolyte layer so that the exposed surface of the negative electrode intermediate layer faced the solid electrolyte layer, and pressure was applied by cold isostatic pressing (CIP) to obtain an evaluation cell (lithium deposition type all-solid-state lithium secondary battery).

[0077] [Example 2] An evaluation cell for this example was prepared in the same manner as in Example 1, except that the amount of solvent added was 16.2 g (polymer compound concentration: 3% by mass) as in the above (preparation of polymer electrolyte solution).

[0078] [Example 3] An evaluation cell for this example was prepared in the same manner as in Example 1, except that the amount of solvent added was 9.5 g (polymer compound concentration: 5% by mass) as described above (preparation of polymer electrolyte solution).

[0079] [Example 4] An evaluation cell for this example was prepared in the same manner as in Example 1, except that the amount of solvent added was 4.5 g (polymer compound concentration: 10% by mass) as in the above (preparation of polymer electrolyte solution).

[0080] The weight of the positive electrode active material layer obtained in Comparative Example 1 (Preparation of positive electrode active material layer) and the weight of the laminate of polymer electrolyte layer (A) and positive electrode active material layer obtained in Examples 1 to 4 (Preparation of laminate of polymer electrolyte layer (A) and positive electrode active material layer) were measured. The results are shown in Table 1 below. The weight after subtracting the weight of the positive electrode active material layer precursor (30 mg) in Examples 1 to 4 (in Table 1, (A) - 30) is also shown. This value indicates the weight of the polymer electrolyte contained in the laminate.

[0081] <Measurement of the thickness of the polymer electrolyte layer (A)> For each of the laminates of the polymer electrolyte layer (A) and the positive electrode active material layer prepared in Examples 1 to 4 above, the thickness of the polymer electrolyte layer (A) was measured on the current collector side (polymer electrolyte layer (A-1)) and the solid electrolyte layer side (polymer electrolyte layer (A-2)) using the following method.

[0082] First, a cross-section parallel to the main surface of the obtained laminate was observed using a scanning electron microscope (SEM) to obtain an image. Next, energy-dispersive X-ray spectroscopy (EDX) was used to map the fluorine (F) element in the obtained image, thereby detecting the presence of the polymer electrolyte (LiTFSI). Similarly, EDX was used to map the sulfur (S) element to detect the presence of the inorganic solid electrolyte, and to map the nickel (Ni) element to detect the presence of the positive electrode active material. Line analysis was performed in the lamination direction, and the thickness of the layer in which only fluorine (F) was detected among the three elements was calculated as the thickness of the polymer electrolyte layer (A). The results are shown in Table 1 below. Furthermore, from the fluorine (F) element mapping results, it was found that the polymer electrolyte layer has a gradient in the polymer electrolyte content in the lamination direction, with the content decreasing from the surface towards the center (not shown).

[0083] <Resistance Measurement of Evaluation Cells> Each evaluation cell prepared in the examples and comparative examples was charged, and its internal resistance was measured using the AC impedance method. Positive leads were connected to the positive and negative current collectors of the evaluation cells prepared above, and CCCV charging was performed with a voltage range of 3.0 to 4.3 V and a charging rate of 0.1 C (0.01 C cutoff). During this process, a constraining pressure of 0.5 to 3 MPa was applied in the stacking direction using a pressing member.

[0084] After charging and allowing a 30-minute rest period, AC impedance measurements were performed using a Solartron electrochemical measurement system (model 12608W) at a temperature of 60°C, with a frequency range of 0.01 Hz to 1 MHz and a voltage amplitude of 10 mV. The internal resistance was then calculated from the Cole-Cole plot obtained from the AC impedance measurements. The results are shown in Table 1 below. The resistance increase rates for each example and comparative example are relative values, with the resistance value at a confinement pressure of 3 MPa set to 100.

[0085]

[0086] From the results in Table 1, it was found that the evaluation cells in Examples 1 to 4 showed a lower rate of resistance increase when the restraining pressure was reduced compared to the evaluation cell in Comparative Example 1.

[0087] 10a Stacked secondary battery, 11' Negative electrode current collector, 11'' Positive electrode current collector, 13 Negative electrode active material layer, 14 Negative electrode intermediate layer, 15 Positive electrode active material layer, 17 Solid electrolyte layer, 19 Single cell layer, 21 Power generation element, 25 Negative electrode current collector plate, 27 Positive electrode current collector plate, 29 Laminate film, 30 Polymer electrolyte layer (A-1), 30' Polymer electrolyte layer (A-2), 31 Polymer electrolyte layer (B).

Claims

1. An electrode comprising: a current collector; an active material layer containing an active material, an inorganic solid electrolyte, a polymer electrolyte, a binder, and a conductive additive; and a polymer electrolyte layer (A) adjacent to the active material layer, located on the surface of the active material layer facing the current collector and on the surface of the active material layer opposite to the current collector, and mainly composed of a polymer electrolyte.

2. The electrode according to claim 1, wherein a polymer electrolyte layer (B) containing a polymer electrolyte as its main component is further disposed on at least a portion of the outer circumference of the active material layer when the power generation element is viewed in plan.

3. The electrode according to claim 1, wherein the total thickness of the polymer electrolyte layer (A) is 2 μm to 15 μm.

4. The electrode according to claim 1, wherein the active material layer has a gradient in the content of the polymer electrolyte in the stacking direction, and the content of the polymer electrolyte present on the surface of the active material layer is higher than the content of the polymer electrolyte present in the central part of the active material layer.

5. The electrode according to claim 1, wherein the content of the polymer electrolyte has a gradient perpendicular to the stacking direction of the active material layer, and the content of the polymer electrolyte present at the edges of the active material layer is higher than the content of the polymer electrolyte present in the central part of the active material layer.

6. The electrode according to claim 1, wherein the thickness of the polymer electrolyte layer (A-1) present on the current collector side of the active material layer is smaller than the thickness of the polymer electrolyte layer (A-2) present on the side of the active material layer opposite to the current collector side.

7. The electrode according to claim 1, wherein the polymer electrolyte contained in the polymer electrolyte layer (A) comprises a polymer compound and a lithium salt, and the lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI).

8. The electrode according to claim 1, wherein the binder comprises polytetrafluoroethylene (PTFE).

9. The electrode according to claim 1, which is the positive electrode.

10. A lithium secondary battery comprising a power generation element having a positive electrode having a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode according to any one of claims 1 to 7.

11. A method for manufacturing an electrode, comprising: mixing an active material, an inorganic solid electrolyte, a conductive additive, and a binder to obtain a mixture; forming an active material layer precursor from the mixture; adding a polymer electrolyte solution containing a polymer electrolyte and a solvent to the active material layer precursor; removing the solvent and drying to form a laminate consisting of an active material layer and a polymer electrolyte layer (A); and arranging a current collector on one side of the laminate.

12. The method for producing an electrode according to claim 11, comprising impregnating the active material layer precursor with the polymer electrolyte solution and adding it.

13. The method for manufacturing an electrode according to claim 11, wherein the binder comprises polytetrafluoroethylene (PTFE).

14. The method for producing an electrode according to claim 11, wherein the mixture and the active material layer precursor do not contain any solvent.

15. The method for producing an electrode according to claim 11, wherein the concentration of the polymer compound in the polymer electrolyte solution is 1 to 10% by mass, based on the total mass of the polymer electrolyte solution.

16. The method for manufacturing an electrode according to claim 11, wherein the solvent is acetonitrile.

17. The method for manufacturing an electrode according to claim 11, wherein the solvent is removed while the active material layer precursor having undergone the polymer electrolyte addition step is placed on the substrate.

18. The method for manufacturing an electrode according to claim 17, further comprising peeling the laminate from the substrate and placing the laminate on a current collector such that the surface of the laminate that was in contact with the substrate is in contact with the current collector.

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