Method for manufacturing lithium secondary battery

Abstract

[Problem] To provide a simple means whereby a lithium secondary battery containing a solid electrolyte can be manufactured. [Solution] One aspect of the present invention relates to a method for manufacturing a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode and containing an electrolyte. Furthermore, this manufacturing method is characterized by comprising an electrolyte layer molding step for heating and pressurizing a lithium ion-conductive composite electrolyte containing an inorganic solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions, thereby deforming the electrolyte into an electrolyte layer having a shape covering at least a portion of the outer periphery of the positive electrode.

Description

Lithium secondary battery manufacturing method

[0001] The present invention relates to a method for producing a lithium secondary battery.

[0002] In recent years, research and development on all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes has been actively conducted. Solid electrolytes are materials primarily composed of ionic conductors that can conduct lithium ions in a solid state. Therefore, all-solid-state lithium secondary batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes that are present in conventional liquid-based lithium secondary batteries.

[0003] WO 2020 / 136971 discloses a technology for improving the reliability of a lithium secondary battery, in which a solid electrolyte layer is disposed so as to cover a positive electrode active material layer, and a sealing member is disposed so as to be located outside the solid electrolyte layer in a plan view, and in a region sandwiched in the stacking direction between a part of the positive electrode current collector and a part of the negative electrode active material layer, and in a region sandwiched in the stacking direction between another part of the positive electrode current collector and a part of the negative electrode current collector, in a cross-sectional view perpendicular to the stacking direction.

[0004] When manufacturing the battery described in WO 2020 / 136971, the electrolyte layer between the electrodes and the sealing member (made of a ceramic material or a resin material) for insulating the electrode periphery are separately manufactured. Therefore, when disposing the electrolyte layer and the sealing member, a slurry (paste) containing each material must be applied and dried. As a result, the battery manufacturing process becomes complicated, and the manufacturing time is lengthened.

[0005] Therefore, an object of the present invention is to provide a means for easily producing a lithium secondary battery containing a solid electrolyte.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and in the process have found that the above-mentioned problems can be solved by heating and pressurizing a composite electrolyte containing an inorganic solid electrolyte and a predetermined mixed salt to form an electrolyte layer having a desired shape when manufacturing a lithium secondary battery, thereby completing the present invention.

[0007] That is, one aspect of the present invention relates to a method for manufacturing a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode and containing an electrolyte. The manufacturing method is characterized by including an electrolyte layer molding step of heating and pressurizing a lithium ion conductive composite electrolyte containing an inorganic solid electrolyte and a mixed salt containing first anions, second anions, and lithium ions to deform the electrolyte into an electrolyte layer having a shape that covers at least a portion of the outer periphery of the positive electrode.

[0008] Fig. 1 is a cross-sectional view schematically showing the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery"), which is one embodiment of a lithium secondary battery manufactured by a manufacturing method according to one aspect of the present invention. Fig. 2 is a diagram for explaining a first embodiment of a manufacturing method for a lithium secondary battery according to this embodiment. Fig. 3 is a diagram for explaining a second embodiment of a manufacturing method for a lithium secondary battery according to this embodiment.

[0009] Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments. Note that the range "X to Y" means "X or more and Y or less."

[0010] One aspect of the present invention is a method for producing a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode and containing an electrolyte, the method including an electrolyte layer forming step of heating and pressurizing a lithium ion conductive composite electrolyte containing an inorganic solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions to deform the electrolyte into an electrolyte layer having a shape that covers at least a portion of the outer periphery of the positive electrode. According to the method for producing a lithium secondary battery of this aspect, a lithium secondary battery containing a solid electrolyte can be produced by a simple means.

[0011] <Lithium Secondary Battery> First, a lithium secondary battery manufactured by the manufacturing method according to this embodiment will be described.

[0012] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter simply referred to as a "stacked-type secondary battery"), which is one embodiment of a lithium secondary battery manufactured by the manufacturing method of the present embodiment. The stacked-type structure allows the battery to be compact and have a high capacity. This specification will be described in detail using the flat stacked, non-bipolar lithium secondary battery (hereinafter simply referred to as a "stacked-type battery") shown in FIG. 1 as an example. However, in terms of the internal electrical connection configuration (electrode structure) of the lithium secondary battery of the present embodiment, it is applicable to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries.

[0013] As shown in FIG. 1 , the stacked secondary battery 10a has a flat, rectangular shape, with a negative electrode current collector 25 and a positive electrode current collector 27 extending from both sides for extracting power. The battery element 21 is wrapped in a battery exterior material (laminated film 29) of the stacked secondary battery 10a, and the periphery is heat-sealed. The battery element 21 is sealed with the negative electrode current collector 25 and the positive electrode current collector 27 extending to the outside. The lithium secondary battery according to this embodiment is not limited to a flat, stacked shape. A wound lithium secondary battery may be cylindrical, or may be a cylindrical battery modified to have a flat, rectangular shape. The cylindrical battery may be housed in a laminated film or a conventional cylindrical can (metal can) as its exterior material, without any particular limitation. Preferably, the battery element is housed inside an aluminum-containing laminated film. This configuration can achieve weight reduction.

[0014] 1, the stacked secondary battery 10a of this embodiment has a structure in which a flat, generally rectangular battery element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior material. Here, the battery element 21 has a structure in which a positive electrode, an electrolyte layer 17, and a negative electrode are stacked. 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'. Specifically, the positive electrode, electrolyte layer, and negative electrode are laminated in this order such that one positive electrode active material layer 15 faces an adjacent negative electrode active material layer 13 with the electrolyte layer 17 interposed therebetween. As a result, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked secondary battery 10a shown in FIG. 1 has a structure in which a plurality of unit cell layers 19 are laminated and electrically connected in parallel. In this case, the outer peripheries of the positive electrode current collector 11" and the positive electrode active material layer 15 are entirely covered with the electrolyte layer 17 except for the lead-out portion of the current collector.

[0015] As shown in FIG. 1 , the outermost positive electrode current collectors located on both outermost layers of the battery element 21 each have a positive electrode active material layer 15 disposed on only one side, but active material layers may be provided on both sides. That is, instead of using a current collector exclusively for the outermost layer with an active material layer provided on only one side, a current collector having active material layers on both sides may be used as the outermost current collector. In some cases, the negative electrode active material layer 13 and the positive electrode active material layer 15 may be used as the negative electrode and positive electrode, respectively, without using current collectors (11′, 11″). The negative electrode current collector 11′ and the positive electrode current collector 11″ are respectively attached with a negative electrode current collector (tab) 25 and a positive electrode current collector (tab) 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are structured so as to be sandwiched between the ends of a laminate film 29, which is the battery exterior material, and extended to the outside of the laminate film 29. The positive electrode current collector 27 and the negative electrode current collector 25 may be attached to the positive electrode current collector 11" and the negative electrode current collector 11' of each electrode by ultrasonic welding, resistance welding, or the like, via a positive electrode lead and a negative electrode lead (not shown) as necessary. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the battery element 21 by a pressure member (not shown). Therefore, the volume of the battery element 21 is kept constant.

[0016] The main components of the lithium secondary battery manufactured by the manufacturing method according to this embodiment will be described below.

[0017] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the material that constitutes the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but an example is 10 to 100 μm.

[0018] [Negative Electrode Active Material Layer] The negative electrode active material layer essentially contains a negative electrode active material. The negative electrode active material layer is typically disposed on the surface of a negative electrode current collector as shown in Fig. 1 . However, if the negative electrode active material layer 13 itself has a certain degree of conductivity, the negative electrode active material layer itself may constitute the negative electrode without using a negative electrode current collector.

[0019] The type of negative electrode active material is not particularly limited, and examples include carbon materials, metal oxides, and metal active materials. Alternatively, lithium-containing active materials such as lithium metal and lithium-containing alloys may be used as the negative electrode active material. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, Sn, Mg, Au, Ag, and Zn. When lithium metal or a lithium-containing alloy is used as the negative electrode active material, 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. The layer of lithium metal deposited on the negative electrode current collector during this charging process becomes the negative electrode active material layer. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer need not be present during full discharge; however, in some cases, a negative electrode active material layer composed of a certain amount of lithium metal may be present during full discharge.

[0020] The negative electrode active material layer contains the lithium ion conductive composite electrolyte and a conductive additive as needed, which can improve the lithium ion conductivity and electrical conductivity of the negative electrode active material layer.

[0021] Examples of conductive additives that can be used in the negative electrode active material layer include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). In addition, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives.

[0022] The negative electrode active material layer may further contain a binder as necessary. The type of binder is not particularly limited, and binders known in the art can be appropriately used. Examples include styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), and carboxymethyl cellulose (CMC). Among these, styrene-butadiene rubber, tetrafluoroethylene, and polyvinylidene fluoride are preferred, and tetrafluoroethylene and polyvinylidene fluoride are more preferred. These binders may be used alone or in combination of two or more.

[0023] The thickness of the negative electrode active material layer (in the case of a lithium deposition type, the thickness at full charge) differs depending on the configuration of the intended lithium secondary battery, but is preferably within the range of, for example, 0.1 to 1000 μm.

[0024] [Electrolyte Layer] The electrolyte layer of the lithium secondary battery produced by the production method according to one embodiment of the present invention is interposed between the negative electrode and the positive electrode, and is characterized by essentially containing the lithium ion conductive composite electrolyte described above. When the electrolyte constituting the electrolyte layer contains the lithium ion conductive composite electrolyte, there is an advantage that the lithium ion conductivity of the electrolyte layer can be improved. Details of the lithium ion conductive composite electrolyte will be described in the section on the production method described later, and therefore will not be described here.

[0025] The content of the electrolyte in the electrolyte layer is preferably 50% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99% by mass or less. The proportion of the lithium ion conductive composite electrolyte in the electrolyte contained in the electrolyte layer is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0026] The electrolyte layer may further contain a binder in addition to the electrolyte. The binder that can be used in the electrolyte layer is the same as that described above for the negative electrode active material layer.

[0027] The thickness of the electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 to 1000 μm, preferably 10 to 40 μm.

[0028] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material. The positive electrode active material layer is typically disposed on the surface of a positive electrode current collector as shown in Fig. 1 . However, if the positive electrode active material layer 15 itself has a certain degree of conductivity, the positive electrode active material layer itself may constitute the positive electrode without using a positive electrode current collector.

[0029] The type of positive electrode active material contained in the positive electrode active material layer is not particularly limited, but a lithium-containing metal oxide is preferred. Specific examples of lithium-containing metal oxides include LiCoO ２ , LiMnO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２Layered 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 ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ , LiVO ２ Among them, Li(Ni-Mn-Co)O ２ and those in which a part of these transition metals is substituted with other elements (NMC composite oxides) are preferably used as the positive electrode active material. These positive electrode active materials may be used alone or in combination of two or more.

[0030] 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.

[0031] The positive electrode active material layer contains the lithium ion conductive composite electrolyte and a conductive additive as needed. This configuration improves the lithium ion conductivity and electrical conductivity of the positive electrode active material layer. The conductive additive that can be used in the positive electrode active material layer is the same as that described for the negative electrode active material layer.

[0032] The positive electrode active material layer may further contain a binder as needed. The binder that can be used in the positive electrode active material layer is the same as that described above for the negative electrode active material layer.

[0033] The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is, for example, 0.1 to 1000 μm, preferably 30 to 300 μm, more preferably 50 to 200 μm, and even more preferably 70 to 150 μm.

[0034] [Positive current collector plate and negative current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive current collector plate 27 and the negative current collector plate 25 may be made of the same material or different materials.

[0035] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, etc., causing electrical leakage and affecting products (for example, automobile parts, particularly electronic devices, etc.).

[0036] [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 battery element, as shown in FIG. 1, can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of its 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 as the exterior material because it allows for easy adjustment of the collective pressure applied to the battery element from the outside.

[0037] The lithium 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 driving power source for EVs and HEVs.

[0038] <<Method for Manufacturing Lithium Secondary Battery>> Next, a manufacturing method according to the present embodiment will be described with reference to the drawings. The manufacturing method according to the present embodiment includes an electrolyte layer molding step in which a lithium ion conductive composite electrolyte is heated and pressurized to deform the composite electrolyte into an electrolyte layer having a shape that covers at least a portion of the outer periphery of a positive electrode. Below, the lithium ion conductive composite electrolyte, which is a specific material used in the electrolyte layer molding step, will be described, followed by an embodiment of the manufacturing method.

[0039] [Lithium Ion Conductive Composite Electrolyte] The lithium ion conductive composite electrolyte (hereinafter also simply referred to as "composite electrolyte") used in the electrolyte layer molding step of a manufacturing method according to one embodiment of the present invention contains an inorganic solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions. Note that, in this specification, the first anion and the second anion have different chemical structures. This composite electrolyte can improve the lithium ion conductivity of a lithium secondary battery. Furthermore, since the mixed salt in the composite electrolyte contains the first anion and the second anion having different chemical structures, it is less likely to crystallize, and the molten salt (also referred to as molten salt) can maintain a liquid state (supercooled liquid state) even below its melting point. The manufacturing method according to this embodiment utilizes these unique features of the composite electrolyte. Therefore, in the composite electrolyte, it is preferable to lower the melting point of the mixed salt to make it liquid or to maintain the liquid state of the mixed salt.

[0040] (Inorganic Solid Electrolyte) The inorganic solid electrolyte refers to a substance made of an inorganic material and having lithium ion conductivity. There are no particular limitations on the specific form of the inorganic solid electrolyte, and conventionally known knowledge can be referred to as appropriate. Examples of inorganic solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, and crystalline solid electrolytes. Among these, from the viewpoint of excellent lithium ion conductivity, the inorganic solid electrolyte preferably contains a sulfide solid electrolyte or an oxide solid electrolyte, and more preferably contains a sulfide solid electrolyte.

[0041] The sulfide solid electrolyte is a solid electrolyte (lithium ion conductor) that essentially contains sulfur (S). The sulfide solid electrolyte essentially contains S, preferably Li, M (where M is at least one selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I), and S, and more preferably S, Li, and P.

[0042] 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 skeleton 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 P ０．７５ 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 ５The 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 (wherein 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 These sulfide solid electrolytes may be used alone or in combination of two or more.

[0043] Examples of oxide solid electrolytes include compounds having a NASICON structure. An example of a compound having a NASICON structure is a compound represented by the general formula Li １＋ｘ Al ｘ Ge ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LAGP), a compound represented by the general formula Li １＋ｘ Al ｘ Ti ２－ｘ (P.O. ４ ) ３ (0≦x≦2) (LATP) and the like. Another example of the oxide solid electrolyte is LiLaTiO (for example, Li ０．３４ La ０．５１ TiO ３ ), LiPON (e.g., Li ２．９ P.O. ３．３ N ０．４６ ), LiLaZrO (e.g., Li ７ La ３ Zr ２ O １２ ) etc.

[0044] In order to further improve the lithium ion conductivity of the composite electrolyte, the lithium ion conductivity of the solid electrolyte at room temperature (25°C) is set to 1 × 10 －５ S / cm or more, and preferably 1×10 －４ S / cm or more is more preferable, and 5×10 －４ S / cm or more is more preferable, and 1×10 －３ The lithium ion conductivity of the solid electrolyte can be measured by an AC impedance method.

[0045] The solid electrolyte preferably has a particulate shape such as a spherical shape or an oval spherical shape. When the solid electrolyte is particulate, its average particle diameter (D ５０ ) is not particularly limited, but is preferably 0.01 μm or more and 40 μm or less, more preferably 0.1 μm or more and 20 μm or less, and even more preferably 0.5 μm or more and 10 μm or less. In this specification, "particle diameter" means the longest distance L between any two points on the contour line of a particle. Furthermore, the value of "average particle diameter" is the arithmetic mean value of the "particle diameters" of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0046] (Mixed Salt) The mixed salt essentially contains a first anion, a second anion, and a lithium ion, and may further contain a third anion and an alkali metal ion (excluding lithium ion). Here, the first anion and the second anion may each form a salt with a lithium ion as a counter ion. In other words, when focusing on the raw materials, the mixed salt can also be said to contain a mixture of a salt consisting of a first anion and a lithium ion (hereinafter simply referred to as a "first lithium salt") and a salt consisting of a second anion and a lithium ion (hereinafter simply referred to as a "second lithium salt"). Similarly, the third anion and an alkali metal ion can form a salt with each other as a counter ion. In other words, when focusing on the raw materials, the mixed salt can also be said to contain a salt consisting of a third anion and an alkali metal ion (hereinafter simply referred to as an "alkali metal salt").

[0047] (First anion and second anion) The first anion and the second anion are not particularly limited in type as long as they are capable of forming a salt with a lithium ion as a counter ion and have different chemical structures. Examples of the first anion and the second anion include an anion represented by Formula 1: ((C ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N － (in formula 1, m and n each independently represent an integer of 0 to 4), a fluorine-containing sulfonylimide anion represented by the following formula 2, a fluorine-containing sulfonylimide anion represented by the following formula 3, PF ６ － (hexafluorophosphate ion), BF ４ － (tetrafluoroborate ion), ClO ４ － (perchlorate ion), AsF ６ － (hexafluoroarsenate ion), CF ３ COO － (trifluoroacetate ion), B(C ２ O４ ) ２ － (bis(oxalato)borate ion). Among these, at least one of the first anion and the second anion is preferably a fluorine-containing sulfonylimide anion represented by the above formula 1, and it is more preferable that both the first anion and the second anion are fluorine-containing sulfonylimide anions represented by the above formula 1.

[0048]

[0049] In the above formula 1, m and n are each independently an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, and even more preferably 0 or 1. When m and n are within the above ranges, the melting point of the mixed salt can be lowered.

[0050] In the composite electrolyte according to this embodiment, the mixed salt preferably contains a bis(fluorosulfonyl)imide anion in which m = n = 0 in the above formula 1 (i.e., the first anion is a bis(fluorosulfonyl)imide anion in which m = n = 0 in the above formula 1). Since the melting point of lithium bis(fluorosulfonyl)imide is relatively low at 145°C, such a configuration can further lower the melting point of the mixed salt.

[0051] In the composite electrolyte according to this embodiment, at least one of the first anion and the second anion is preferably an asymmetric anion where m≠n in Formula 1, and more preferably both the first anion and the second anion are asymmetric anions where m≠n in Formula 1. Because salts formed from asymmetric anions are difficult to crystallize, such a configuration can lower the melting point of the mixed salt.

[0052] When the first anion is a bis(fluorosulfonyl)imide anion in which m = n = 0 in the above formula 1, the content of the first anion in the mixed salt is preferably 20 to 80 mol%, more preferably 30 to 70 mol%, and even more preferably 40 to 60 mol%, based on the total number of moles of the first anion and the second anion. This configuration can further lower the melting point of the mixed salt. In one embodiment, when the first anion is a bis(fluorosulfonyl)imide anion in which m = n = 0 in the above formula 1, the content of the first anion in the mixed salt is preferably 40 to 80 mol%, more preferably 50 to 70 mol%, and even more preferably 55 to 65 mol%, based on the total number of moles of the first anion and the second anion.

[0053] (Lithium ions) Lithium ions are present in the mixed salt as counter ions of the first anions and the second anions. Therefore, when the mixed salt is composed of the first anions, the second anions, and lithium ions, the number of moles of lithium ions is substantially equal to the total number of moles of the first anions and the second anions.

[0054] (Tertiary Anion and Alkali Metal Ion) The mixed salt may further contain a tertiary anion and an alkali metal ion other than lithium ion (also simply referred to as "alkali metal ion"). By containing the tertiary anion and the alkali metal ion, the melting point of the mixed salt may be lowered.

[0055] The type of third anion is not particularly limited. Examples of the third anion include the same anions used as the first anion and second anion. Among these, the third anion is preferably a fluorine-containing sulfonylimide anion represented by the above formula 1. In this case, in the above formula 1, m and n are each independently preferably an integer of 0 to 3, more preferably an integer of 0 to 2, even more preferably 0 or 1, and particularly preferably 1. When m and n are within the above ranges, the melting point of the mixed salt may be lowered. The third anion may be used alone, or two or more types may be used in combination. The third anion may be the same as or different from either one or both of the first anion and second anion. The third anion may be used alone, or two or more types may be used in combination.

[0056] The type of alkali metal ion is not particularly limited, but is preferably at least one selected from the group consisting of sodium ions, potassium ions, rubidium ions, and cesium ions. The alkali metal ions may be used alone or in combination of two or more.

[0057] When the mixed salt contains a third anion and an alkali metal ion, the content of the alkali metal ion is preferably more than 0 mol % and not more than 33 mol %, more preferably more than 1 mol % and not more than 30 mol %, even more preferably 2 mol % to 25 mol %, particularly preferably 3 mol % to 20 mol %, and most preferably 4 mol % to 15 mol % relative to the total number of moles of the lithium ion and alkali metal ion contained in the mixed salt. When the content of the alkali metal ion is within the above range, it is possible to further lower the melting point of the mixed salt while suppressing a decrease in the transport number.

[0058] The mixed salt can be prepared by mixing a salt consisting of a first anion and lithium ions (first lithium salt), a salt consisting of a second anion and lithium ions (second lithium salt), and a salt consisting of an optionally added third anion and alkali metal ions (alkali metal salt). More specifically, first, predetermined amounts of the first lithium salt, the second lithium salt, and the optionally added alkali metal salt are weighed out. These are then mixed while heating. The heating temperature is not particularly limited, but is preferably set to a temperature equal to or higher than the lower of the melting points of the first and second lithium salts and equal to or lower than the reference temperature +15°C, more preferably equal to or higher than the reference temperature and equal to or lower than the reference temperature +10°C. This allows one salt to melt, and then the other salt dissolves in the molten salt. This allows a mixed salt in which the ions are uniformly mixed. The mixed salt obtained in this manner may have a melting point lower than the reference temperature. That is, according to a preferred embodiment, the melting point of the mixed salt is lower than the melting points of the salt composed of the first anion and lithium ions and the salt composed of the second anion and lithium ions. This configuration allows the mixed salt to melt at a lower temperature. In this specification, the melting point can be determined as the peak top temperature of the melting peak in the heat of fusion curve when heated at a rate of 10°C / min using a differential scanning calorimetry (DSC) device.

[0059] The melting point of the mixed salt is not particularly limited, but is preferably 180° C. or lower, more preferably 160° C. or lower, even more preferably 150° C. or lower, particularly preferably 140° C. or lower, and most preferably 130° C. or lower. The melting point of the mixed salt is preferably 10° C. or higher.

[0060] The composite electrolyte according to this embodiment may contain anions and cations other than the first anion, the second anion, and lithium ions, as well as optional third anions and alkali metal ions, as long as the effects of the present invention are not significantly impaired. However, from the viewpoint of suppressing a decrease in the transference number, it is preferable that the composite electrolyte is substantially free of cations other than lithium ions and alkali metal ions, and more preferably substantially free of organic cations. In this specification, "substantially free" means that the content is 3% by mass or less, preferably 2% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass.

[0061] In the composite electrolyte according to this embodiment, the content of the inorganic solid electrolyte is preferably 11 to 98 mass %, more preferably 20 to 97 mass %, even more preferably 30 to 96 mass %, and even more preferably 40 to 95 mass %, relative to 100 mass % of the total mass of the lithium ion conductive composite electrolyte. When the content of the inorganic solid electrolyte is within the above range, high lithium ion conductivity can be ensured.

[0062] The composite electrolyte according to the present embodiment contains an inorganic solid electrolyte and a mixed salt. As described above, the mixed salt contains a first anion and a second anion having different chemical structures, making it difficult to crystallize. The molten salt can maintain a liquid state (supercooled liquid state) even below its melting point. Therefore, when the mixed salt is in a liquid state, the composite electrolyte becomes a mixture of a solid and a liquid. In this case, the composite electrolyte is preferably clay-like. In this specification, "clay-like" refers to a state in which a plastic deformation is possible. Here, "plastic deformation" refers to a deformation that persists even after an external force is applied to an object and then removed. Therefore, a state in which the shape changes after the external force is removed (a paste-like state) or a state in which the object crumbles without deformation when an external force is applied to the object (a cake-like state) is not included in the term clay-like. Methods for controlling the clay-like state of a composite electrolyte include changing the content of the mixed salt in the composite electrolyte and changing the size of the solid content (particularly, the particle size of the solid electrolyte). The higher the content of the mixed salt and the smaller the size of the solids, the more the composite electrolyte approaches a paste state rather than a clay state.

[0063] The composite electrolyte can be produced by appropriately mixing the mixed salt and an inorganic solid electrolyte, although there are no particular limitations on the mixed salt. It is preferable that the mixed salt is liquid when mixed. That is, the composite electrolyte is preferably produced by permeating the voids of the inorganic solid electrolyte with the mixed salt in a liquid state. A composite electrolyte having such a configuration is preferable because it can be produced by a simple operation of permeating a liquid (mixed salt) into a solid (inorganic solid electrolyte). Furthermore, the mixed salt may be mixed while being heated to a temperature above its melting point, if necessary.

[0064] 2 is a diagram illustrating a first embodiment of a method for manufacturing a lithium secondary battery according to the present invention. In the manufacturing method of the present embodiment, after the electrolyte layer molding step, the electrolyte layer is laminated with a positive electrode and a negative electrode to produce a battery element.

[0065] More specifically, in this embodiment, as shown in FIG. 2( a), an electrolyte layer molding step is first carried out to prepare an "electrolyte layer having a shape that covers at least a portion of the outer periphery of the positive electrode." Note that in FIG. 2, similarly to FIG. 1, the outer peripheries of the positive electrode current collector 11" and the positive electrode active material layer 15 are entirely covered with the electrolyte layer 17, except for the lead-out portion of the current collector. However, from the viewpoint of preventing short circuits through the side surfaces of the battery element, it is preferable that the outer peripheries of the negative electrode current collector 11' and the negative electrode active material layer 13 are also entirely covered with the electrolyte layer 17, except for the lead-out portion of the current collector.

[0066] When preparing an electrolyte layer having a desired shape in the electrolyte layer formation step, a sheet-like electrolyte layer precursor 17' is prepared by adjusting the lithium ion conductive composite electrolyte to the desired electrolyte layer size. This electrolyte layer precursor 17' is then heated and pressurized in the stacking direction from above and below using a cathode die 31 and an anode die 33. As described above, the lithium ion conductive composite electrolyte has a lower melting point than other electrolytes. Therefore, the above-described heating and pressurizing treatments result in an electrolyte layer 17 having a desired shape. Note that, as long as an electrolyte layer having a desired shape can be obtained, the heating and pressurizing treatments may be performed simultaneously, or the pressurizing treatment may be performed after the heating treatment. Furthermore, it is preferable that the heating and pressurizing treatments at this stage be performed only once, but in some cases, at least one of the treatments may be performed two or more times.

[0067] The heating temperature during the heat treatment is not particularly limited, provided that it is a temperature sufficient to melt the lithium ion conductive composite electrolyte and deform it by pressure. The heating temperature is, for example, 100 to 200°C, and preferably 110 to 160°C. The pressure applied during the pressure treatment is also not particularly limited, provided that it is sufficient to deform the melted composite electrolyte by heating. The pressure is, for example, 0.5 to 10 MPa, and preferably 1 to 5 MPa.

[0068] Subsequently, the electrolyte layer 17 produced as described above is laminated on a positive electrode (a laminate of a positive electrode current collector 11″ and a positive electrode active material layer 15) and a negative electrode (a laminate of a negative electrode current collector 11′ and a negative electrode active material layer 13) as shown in FIG. 2( b) to produce a battery element 21. At this time, the electrolyte layer 17 produced in the electrolyte layer production step does not need to be laminated on the positive electrode and the negative electrode simultaneously, and the electrolyte layer 17 may be laminated on the positive electrode in advance, and then on the negative electrode.

[0069] Furthermore, after laminating the electrolyte layer 17 with the positive electrode (or the positive electrode and the negative electrode), it is preferable to reheat and repressurize the electrolyte layer. This can improve the adhesion between the electrolyte layer 17 and the positive electrode (or the positive electrode and the negative electrode), thereby reducing the contact resistance. Here, the heating temperature during reheating is preferably lower than the heating temperature during heating in the electrolyte layer molding process described above. Furthermore, the pressure during repressurization is preferably lower than the pressure during pressurization in the electrolyte layer molding process described above. By adopting such heating and pressurization conditions, it is possible to minimize changes in the shape of the molded electrolyte layer while reducing the contact resistance between the electrolyte layer and the electrode. Note that, as long as the above-mentioned objective is achieved, the reheating treatment and repressurization treatment may be performed simultaneously, or the repressurization treatment may be performed after the reheating treatment is completed. Furthermore, it is preferable that the reheating treatment and the repressurization treatment are each performed only once, but in some cases, at least one of the treatments may be performed two or more times.

[0070] In the manufacturing method according to the present embodiment, it is preferable that the steps other than the electrolyte layer molding step (except for the reheating treatment described above) are performed at a temperature lower than the temperature at which the composite electrolyte exhibits fluidity. By adopting such a configuration, it is possible to eliminate the heating step that requires time to heat the components, thereby shortening the battery manufacturing time.

[0071] According to this embodiment, an electrolyte layer having a desired shape and containing a composite electrolyte is prepared in advance, and then laminated on an electrode to produce a battery element. This has the advantage of significantly reducing the number of steps required for manufacturing a battery. For example, it is possible to eliminate steps such as applying an electrolyte slurry to the surface of the electrode and drying it, and applying pressure to prepare each single layer each time an electrode-electrolyte layer laminate is prepared. It is also possible to improve the alignment accuracy during lamination, which can contribute to improving workability. Furthermore, it is possible to obtain the effect of reducing contact resistance between the electrode and the electrolyte layer, and the effect of preventing short circuits through the side surfaces by covering the outer periphery of the positive electrode active material layer with the electrolyte layer.

[0072] Second Embodiment Fig. 3 is a diagram for explaining a second embodiment of the method for producing a lithium secondary battery according to the present embodiment. In the production method of this embodiment, a lithium ion conductive composite electrolyte is laminated with a positive electrode and a negative electrode, and then the electrolyte layer molding step is performed to produce a battery element. In this respect, it differs from the first embodiment described above. Unless otherwise specified below, the preferred embodiments described in the first embodiment are also adopted as preferred embodiments in the second embodiment.

[0073] More specifically, in this embodiment, first, as shown in FIG. 3( a), a sheet-like electrolyte layer precursor 17′, which is prepared by adjusting the above-described lithium ion conductive composite electrolyte to a desired electrolyte layer size, is laminated on a positive electrode (a laminate of a positive electrode current collector 11″ and a positive electrode active material layer 15) and a negative electrode (a laminate of a negative electrode current collector 11′ and a negative electrode active material layer 13) to prepare a battery element precursor 21′.

[0074] Next, the battery element precursor 21′ produced as described above is subjected to a heat treatment and a pressure treatment in the stacking direction. As described above, a lithium ion conductive composite electrolyte is characterized by having a lower melting point than other electrolytes. For this reason, in this embodiment as well, as shown in FIG. 3(b), an electrolyte layer 17 having a desired shape is obtained by undergoing the heat treatment and pressure treatment as described above, and a battery element 21 including this is obtained. Note that in this embodiment, the shape of the electrolyte layer 17 covers the outer periphery of both the positive electrode current collector 11″ and the negative electrode current collector 11′ except for the lead-out portions. With this configuration, it is possible to reduce the stress applied to the current collectors when stacking the battery element 21, and as a result, it is possible to prevent the current collectors from breaking.

[0075] The heating temperature and pressure during the heat treatment are not particularly limited, but may be sufficient to melt the lithium ion conductive composite electrolyte and deform it under pressure. In particular, the heating temperature is preferably a temperature at which the lithium ion conductive composite electrolyte exhibits fluidity and is lower than the temperature at which components other than the lithium ion conductive composite electrolyte undergo chemical reactions or state changes. The heating temperature is, for example, 100 to 200°C, preferably 110 to 160°C. By adopting such a pressure temperature, the composite electrolyte is imparted with fluidity while reducing the risk of side reactions or changes to a liquid state in other components. As a result, the composite electrolyte can be handled as a solid component that does not react with other components, simplifying the manufacturing process while ensuring safety during battery manufacturing and the quality of the manufactured battery.

[0076] Furthermore, the pressure applied is preferably a pressure that deforms the lithium ion conductive composite electrolyte and is lower than the pressure that causes plastic deformation of components other than the lithium ion conductive composite electrolyte. The pressure is, for example, 0.5 to 10 MPa, and preferably 1 to 5 MPa. By employing such a pressure, the composite electrolyte is deformed while reducing the risk of deformation of other components. As a result, the other components can be handled as solid components that do not deform, and the manufacturing process can be simplified while ensuring safety during battery manufacturing and the quality of the manufactured battery.

[0077] According to this embodiment, the lithium ion conductive composite electrolyte is laminated with the positive electrode and the negative electrode, and then the electrolyte layer molding step is performed to produce a battery element. This allows molding of the electrolyte layer using the composite electrolyte and laminating and pressing the electrolyte layer with other components such as electrodes simultaneously. As a result, the number of steps required for manufacturing a battery can be significantly reduced. Furthermore, the contact resistance between the electrode and the electrolyte layer can be reduced, and the outer periphery of the positive electrode active material layer is covered with the electrolyte layer, thereby preventing short circuits through the side surfaces.

[0078] The following items are also included within the scope of the present invention: Item 1: A method for producing a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode and containing an electrolyte, the method comprising: an electrolyte layer-forming step of heating and pressurizing a lithium ion-conductive composite electrolyte containing an inorganic solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions, to deform the lithium ion-conductive composite electrolyte into an electrolyte layer having a shape that covers at least a part of the outer periphery of the positive electrode; Item 2: A method for producing a lithium secondary battery according to Item 1, wherein the shape covers at least a part of the outer periphery of the negative electrode; Item 3: A method for producing a lithium secondary battery according to Item 1 or 2, further comprising, after the electrolyte layer-forming step, laminating the electrolyte layer with the positive electrode, or laminating the electrolyte layer with the positive electrode and the negative electrode to produce a battery element; Item 4: A method for producing a lithium secondary battery according to Item 3, further comprising reheating and repressurizing the electrolyte layer after laminating it with the positive electrode; Item 5: A method for producing a lithium secondary battery according to Item 4, wherein the heating temperature during the reheating is lower than the heating temperature during the heating in the electrolyte layer molding step, and the pressure during the re-pressurizing is lower than the pressure during the pressurizing in the electrolyte layer molding step; Item 6: A method for producing a lithium secondary battery according to Item 1 or 2, comprising laminating the lithium ion conductive composite electrolyte with the positive electrode and the negative electrode, and then performing the electrolyte layer molding step to produce a battery element; Item 7: A method for producing a lithium secondary battery according to Item 6, wherein the heating temperature during the heating in the electrolyte layer molding step is a temperature at which the lithium ion conductive composite electrolyte exhibits fluidity and is lower than a temperature at which components other than the lithium ion conductive composite electrolyte undergo a chemical reaction or a state change; Item 8: A method for producing a lithium secondary battery according to Item 6 or 7, wherein the pressure during the pressurizing in the electrolyte layer molding step is a pressure at which the lithium ion conductive composite electrolyte deforms and is lower than a pressure at which components other than the lithium ion conductive composite electrolyte undergo plastic deformation;Item 9: A method for producing a lithium secondary battery according to any one of Items 1 to 8, wherein steps other than the electrolyte layer molding step are carried out at a temperature lower than the temperature at which the lithium ion conductive composite electrolyte exhibits fluidity; Item 10: A method for producing a lithium secondary battery according to any one of Items 1 to 9, wherein the positive electrode and / or the negative electrode include a current collector and an electrode active material layer, and the shape is a shape that covers the entire outer periphery of the positive electrode except for an extraction portion of the current collector, or a shape that covers the entire outer periphery of the positive electrode and the negative electrode; Item 11: A method for producing a lithium secondary battery according to any one of Items 1 to 10, wherein the positive electrode and / or the negative electrode include a current collector and an electrode active material layer, and the shape is a shape that covers the outer periphery except for an extraction portion of the current collector; Item 12: A method for producing a lithium secondary battery according to any one of Items 1 to 11, wherein the melting point of the mixed salt is lower than the melting point of the salt composed of the first anion and lithium ions and the melting point of the salt composed of the second anion and lithium ions; Item 13: The first anion and the second anion are each represented by Formula 1: ((C; ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N －(in Formula 1, m and n each independently represent an integer of 0 to 4); Item 14: The method for producing a lithium secondary battery according to any one of Items 1 to 13, wherein the first anion is a (fluorosulfonyl)imide anion; Item 15: The method for producing a lithium secondary battery according to any one of Items 1 to 14, wherein the mixed salt further contains a third anion and an alkali metal ion (excluding lithium ions); Item 16: The method for producing a lithium secondary battery according to any one of Items 1 to 15, wherein the lithium ion conductive composite electrolyte is substantially free of organic cations; Item 17: The method for producing a lithium secondary battery according to any one of Items 1 to 16, wherein the inorganic solid electrolyte comprises an oxide solid electrolyte or a sulfide solid electrolyte; Item 18: The method for producing a lithium secondary battery according to any one of Items 1 to 17, wherein the lithium ion conductive composite electrolyte is formed by infiltrating the mixed salt in a liquid state into voids in the inorganic solid electrolyte.

[0079] The present invention will be described in more detail below using experimental examples. However, the technical scope of the present invention is not limited to the following experimental examples. Note that the following operations were carried out in a glove box at room temperature (25°C) with a dew point of -68°C or less. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0080] <Examples of Manufacturing Lithium Ion Conductive Composite Electrolyte> (Experimental Example 1) A total of 2 g of lithium bis(fluorosulfonyl)imide (LiFSA, melting point 418 K (145°C), salt composed of a first anion and lithium ions) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSA, melting point 511 K (238°C), salt composed of a second anion and lithium ions) were weighed out to a molar ratio of first anion:second anion = 6:4 and placed in a beaker. This beaker was placed on a hot stirrer and heated at 428 K (155°C) for 10 minutes to melt the LiFSA. A stirrer was then placed in the beaker, and the mixture was heated at 428 K (155°C) for 1 hour while stirring at 50 to 100 rpm to dissolve the LiTFSA. As a result, a liquid mixed salt (Li([FSA] 0.6 [TFSA] 0.4, melting point 391 K (118°C)) was obtained. When the liquid mixed salt was stored at room temperature, it maintained a supercooled liquid state for about one month.

[0081] Five parts by mass of the liquid mixed salt was weighed and placed in a mortar. ６ P.S. ５ 95 parts by mass of sulfide solid electrolyte (C1, average particle diameter 1.0 μm) was weighed out and placed in the mortar, and the mixed salt and sulfide solid electrolyte were thoroughly mixed to obtain a lithium ion conductive composite electrolyte of this experimental example.

[0082] (Experimental Example 2) A liquid mixed salt prepared by the same method as in Experimental Example 1 and a stirring bar were placed in a container, and Li as an unsintered oxide electrolyte was added. １．３ Al ０．３ Ti １．７ (P.O. ４ ) ３ (manufactured by Toshima Manufacturing Co., Ltd., average particle size: 1 μm, also referred to in this specification as "LATP") was added so that the mass ratio of LATP:Li([FSA]0.6[TFSA]0.4) was 0.9:1, and the mixture was heated to 155°C (428 K) using a hot magnetic stirrer, and then stirred at the same temperature at a rotation speed of 50 to 300 rpm using the hot magnetic stirrer for 1 hour, thereby obtaining a lithium ion conductive composite electrolyte of Experimental Example 2.

[0083] Comparative Experimental Example 1 Without adding any mixed salt, LATP (manufactured by Toshima Manufacturing Co., Ltd., average particle size: 1 μm) was used as an unsintered oxide electrolyte as is for this comparative experimental example.

[0084] <Measurement of ionic conductivity> 100 mg of the electrolyte of Example 2 was placed on a cylindrical stainless steel (SUS) electrode. Another cylindrical stainless steel electrode was then placed on top to sandwich the electrolyte, and the electrodes were pressed at a pressure of 40 MPa using a uniaxial press to produce a SUS / electrolyte / SUS laminate. A laminate was also obtained using the electrolyte of Comparative Experimental Example 1 in the same manner.

[0085] The laminates of Experimental Example 2 and Comparative Experimental Example 1 obtained above were subjected to AC impedance measurement (PEIS). From the results of this AC impedance measurement, the ionic conductivity values ​​for lithium ions of the electrolytes of Experimental Example 2 and Comparative Experimental Example 1 were calculated. The measurements were carried out on a hot magnetic stirrer set at 80°C, with a measurement frequency of 10 mHz to 50 kHz, an applied voltage of OCV, and a voltage amplitude of 500 mV. As a result, the ionic conductivity of the electrolyte of Experimental Example 2 was 5.6 × 10 －６ In the measurement of Comparative Experiment 1, the electrolyte was not conductive and measurement was not possible.

[0086] This application claims priority to Japanese Patent Application No. 2024-131946, filed on August 8, 2024, the contents of which are incorporated herein by reference in their entirety.

[0087] REFERENCE SIGNS LIST 10a laminated battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 electrolyte layer, 17' electrolyte layer precursor, 19 unit cell layer, 21 battery element, 21' battery element precursor, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film, 31 positive electrode stamping die, 33 negative electrode stamping die.

Claims

1. A method for manufacturing a lithium secondary battery comprising a positive electrode, a negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode and containing an electrolyte, the method comprising an electrolyte layer forming step of heating and pressurizing a lithium ion conductive composite electrolyte containing an inorganic solid electrolyte and a mixed salt containing first and second anions and lithium ions to deform the lithium ion conductive composite electrolyte into an electrolyte layer having a shape that covers at least a portion of the outer periphery of the positive electrode.

2. The method for producing a lithium secondary battery according to claim 1, wherein the shape is a shape that covers at least a part of the outer periphery of the negative electrode.

3. The method for producing a lithium secondary battery according to claim 1 or 2, further comprising, after the electrolyte layer molding step, laminating the electrolyte layer with the positive electrode, or laminating the electrolyte layer with the positive electrode and the negative electrode to produce a battery element.

4. The method for producing a lithium secondary battery according to claim 3, further comprising reheating and repressurizing the electrolyte layer after lamination with the positive electrode.

5. A method for producing a lithium secondary battery according to claim 4, wherein the heating temperature during the reheating is lower than the heating temperature during the heating in the electrolyte layer molding step, and the pressure during the repressurizing is lower than the pressure during the pressurizing in the electrolyte layer molding step.

6. A method for producing a lithium secondary battery according to claim 1 or 2, comprising laminating the lithium ion conductive composite electrolyte with the positive electrode and the negative electrode, and then carrying out the electrolyte layer molding step to produce a battery element.

7. The method for producing a lithium secondary battery according to claim 6, wherein the heating temperature in the electrolyte layer molding step is a temperature at which the lithium ion conductive composite electrolyte exhibits fluidity, and is lower than a temperature at which components other than the lithium ion conductive composite electrolyte undergo a chemical reaction or change in state.

8. The method for producing a lithium secondary battery according to claim 6, wherein the pressure applied in the electrolyte layer molding step is a pressure that deforms the lithium ion conductive composite electrolyte but is lower than a pressure that causes plastic deformation of members other than the lithium ion conductive composite electrolyte.

9. The method for producing a lithium secondary battery according to claim 1 or 2, wherein steps other than the electrolyte layer forming step are carried out at a temperature lower than the temperature at which the lithium ion conductive composite electrolyte exhibits fluidity.

10. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the positive electrode and / or the negative electrode comprises a current collector and an electrode active material layer, and the shape is a shape that covers the entire outer periphery of the positive electrode except for an extraction portion of the current collector, or a shape that covers the entire outer periphery of the positive electrode and the negative electrode.

11. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the positive electrode and / or the negative electrode comprises a current collector and an electrode active material layer, and the shape covers the outer periphery of the current collector except for the removal portion.

12. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the melting point of the mixed salt is lower than the melting point of the salt composed of the first anion and lithium ions and the melting point of the salt composed of the second anion and lithium ions.

13. The first anion and the second anion are each represented by Formula 1: ((C ｍ F ２ｍ＋１ ) SO ２ ) ((C ｎ F ２ｎ＋１ ) SO ２ ) N － 3. The method for producing a lithium secondary battery according to claim 1, wherein m and n are each independently an integer of 0 to 4.

14. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the first anion is a bis(fluorosulfonyl)imide anion.

15. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the mixed salt further contains a third anion and an alkali metal ion (excluding lithium ion).

16. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the lithium ion conductive composite electrolyte is substantially free of organic cations.

17. The method for producing a lithium secondary battery according to claim 1 or 2, wherein the inorganic solid electrolyte includes an oxide solid electrolyte or a sulfide solid electrolyte.

18. A method for producing a lithium secondary battery according to claim 1 or 2, wherein the lithium ion conductive composite electrolyte is formed by permeating the mixed salt in a liquid state into the voids of the inorganic solid electrolyte.

Images