Lithium ion conductive composite electrolyte, composite electrolyte layer using same, electrode active material layer and lithium secondary battery, and control device and operation method for said lithium secondary battery

Abstract

The present disclosure addresses the problem of providing a means capable of improving lithium ion conductivity in a lithium secondary battery. Provided is a lithium ion conductive composite electrolyte containing a sulfide solid electrolyte, and a mixed salt containing first anions, second anions, and lithium ions.

Description

Lithium ion conductive composite electrolyte, composite electrolyte layer using the same, electrode active material layer and lithium secondary battery, and method and control device for operating the lithium secondary battery

[0001] The present invention relates to a lithium ion conductive composite electrolyte, a composite electrolyte layer, an electrode active material layer and a lithium secondary battery using the same, and an operating method and control device for the 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] On the other hand, in all-solid-state lithium secondary batteries, lithium ion conductivity is exhibited by contact between particles via the solid electrolyte, and therefore, compared to conventional liquid-based lithium secondary batteries, it is difficult to ensure the desired lithium conductivity.

[0004] To address such problems, for example, Japanese Patent Application Laid-Open No. 2024-058768 (corresponding to the specification of U.S. Patent Application Publication No. 2024 / 0128433) discloses an electrode for an all-solid-state battery including an active material layer containing an active material, a first solid electrolyte, and a second solid electrolyte. In the electrode for an all-solid-state battery, the active material, the first solid electrolyte, and the second solid electrolyte are represented by the formula (1): G ２ <G １ <G Ａ (In formula (1), G Ａ indicates the compressive elastic modulus of the active material, and G １ represents the compressive elastic modulus of the first solid electrolyte, and G ２ represents the compressive elastic modulus of the second solid electrolyte). The active material and the first solid electrolyte satisfy the relationship of formula (2): 0.41r Ａ <r １ (In formula (2), r Ａ denotes the particle radius of the active material, and r １indicates the particle radius of the first solid electrolyte). According to the above document, the first solid electrolyte, which has a relatively high compressive modulus, elastically deforms when the active material layer is compressed, thereby maintaining its shape without being crushed. The second solid electrolyte, which has a relatively low compressive modulus, plastically deforms and fills the voids between the active materials. As a result, it is said that three-dimensionally connected ion conduction paths (trunk-shaped ion conduction paths formed by the first solid electrolyte and ion conduction paths formed by the second solid electrolyte extending in branch-like shapes from the trunk) are formed within the active material layer.

[0005] However, according to the investigations of the present inventors, it has been found that when the electrodes for all-solid-state batteries described in the above documents are applied to lithium secondary batteries, sufficient lithium ion conductivity may not be exhibited.

[0006] Therefore, an object of the present invention is to provide a means for improving the lithium ion conductivity in a lithium secondary battery.

[0007] 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 using a composite electrolyte in which a mixed salt composed of two types of anions and lithium ions is contained in a sulfide solid electrolyte, and have thus completed the present invention.

[0008] That is, one aspect of the present invention is a lithium ion conductive composite electrolyte containing a sulfide solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions.

[0009] Fig. 1 is a cross-sectional view showing a schematic diagram of the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (hereinafter also referred to simply as a "stacked-type secondary battery") according to one embodiment of the present invention. Fig. 2 is a time chart of voltage and current when switching between charge and discharge. Fig. 3 shows the electric double layer capacity C depending on the cell pressure. ｄｌ Fig. 4 is a schematic diagram of a control device for a lithium secondary battery according to one embodiment of the present invention. Fig. 5 is a graph plotting the relationship between press pressure and resistance value for the blocking cells of Test Examples 1 to 3 and Comparative Test Examples 1 to 3.

[0010] 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."

[0011] <Lithium Ion Conductive Composite Electrolyte> A lithium ion conductive composite electrolyte (hereinafter also simply referred to as "composite electrolyte") according to one embodiment of the present invention contains a sulfide solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions. In this specification, the first anion and the second anion have different chemical structures. The lithium ion conductive composite electrolyte according to this embodiment can improve the lithium ion conductivity in a lithium secondary battery. The mechanism by which the lithium ion conductive composite electrolyte according to this embodiment achieves the above-mentioned effects is not fully understood, and the present invention is not bound by any theory. However, the following mechanism is presumed. During operation of a lithium secondary battery, contact between the electrode active material and the solid electrolyte may be insufficient. For example, expansion and contraction of the electrode active material due to charge and discharge may cause peeling at the interface between the electrode active material and the solid electrolyte in the electrode active material layer, thereby breaking the lithium ion conduction path between the electrode active material and the solid electrolyte. This may result in a decrease in lithium ion conductivity in the lithium secondary battery. In the lithium ion conductive composite electrolyte according to the present embodiment, the mixed salt contains a first anion and a second anion having different chemical structures, and therefore is less likely to crystallize. The molten salt (also referred to as a molten salt) can maintain a liquid state (supercooled liquid state) even below its melting point. By applying a composite electrolyte containing such a mixed salt and a sulfide solid electrolyte to the electrode active material layer of a lithium secondary battery, even if the electrode active material expands and contracts during charging and discharging, causing particles of the electrode active material and particles of the sulfide solid electrolyte in the electrode active material layer to separate, the mixed salt can penetrate into the voids between these particles and establish an ion conduction path between the particles. Furthermore, the expansion and contraction of the electrode active material during charging and discharging can sometimes cause delamination at the interface between the electrode active material in the electrode active material layer and the solid electrolyte in the electrolyte layer at the interface between the electrode active material layer and the electrolyte layer, resulting in the ion conduction path being severed.By applying the composite electrolyte according to this embodiment to the electrolyte layer of a lithium secondary battery, even when particles of the electrode active material in the electrode active material layer and particles of the sulfide solid electrolyte in the electrolyte layer are separated, the ion conduction path between the particles can be regenerated by the same mechanism as described above. This improves the lithium ion conductivity of the lithium secondary battery and ultimately reduces resistance. The mixed salt may become solid at temperatures below its melting point, making it difficult for the mixed salt to fill the interparticle voids. Even in such cases, for example, by raising the temperature of the lithium secondary battery above its melting point to melt (liquefy) the mixed salt, the interparticle voids can be refilled with the mixed salt, thereby suppressing or eliminating the decrease in lithium ion conductivity due to poor interparticle contact. In the lithium ion conductive composite electrolyte according to this embodiment, it is preferable to lower the melting point of the mixed salt to make the mixed salt liquid or to maintain the liquid state of the mixed salt.

[0012] The configuration of the lithium ion conductive composite electrolyte according to this embodiment will be described in detail below.

[0013] [Sulfide Solid Electrolyte] The sulfide solid electrolyte is a solid electrolyte (lithium ion conductor) that essentially contains sulfur (S). From the viewpoint of further improving the lithium ion conductivity of the lithium ion conductive composite electrolyte, the sulfide solid electrolyte has a lithium ion conductivity of 1×10 at room temperature (25° C.). －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 sulfide solid electrolyte can be measured by an AC impedance method.

[0014] The sulfide solid electrolyte essentially contains the S element, preferably contains the Li element, the M element (wherein M 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 the S element, and more preferably contains the S element, the Li element, and the P element.

[0015] 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. ５X (wherein X is Cl, Br or I). ２ S-P ２ S ５ " is written by Li ２ S and P ２ S ５ The same applies to other descriptions. Among them, the sulfide solid electrolyte is preferably LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (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 is selected from the group consisting of:

[0016] 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).

[0017] The sulfide solid electrolyte may be used alone or in combination of two or more kinds.

[0018] [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").

[0019] (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. By adopting such a configuration, the melting point of the mixed salt can be further lowered.

[0020]

[0021] 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.

[0022] In the lithium ion conductive 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.

[0023] In the lithium ion conductive 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.

[0024] 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.

[0025] (Lithium ions) Lithium ions exist in the mixed salt as counter ions of the first anion and the second anion. Therefore, when the anions contained in the mixed salt consist only of the first anion and the second anion, the number of moles of lithium ions can be substantially equal to the total number of moles of the first anion and the second anion.

[0026] (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.

[0027] 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 0. 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 140° C. or lower, and particularly preferably 130° C. or lower. The melting point of the mixed salt is preferably 10° C. or higher.

[0032] The lithium ion conductive 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 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, "organic cation" refers to a positively charged ion containing a carbon atom. 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.

[0033] In the lithium ion conductive composite electrolyte according to this embodiment, the content of the sulfide 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 sulfide solid electrolyte is within the above range, high lithium ion conductivity can be ensured.

[0034] The lithium ion conductive composite electrolyte according to the present embodiment contains a sulfide 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 lithium ion conductive composite electrolyte becomes a mixture of a solid and a liquid. In this case, the lithium ion conductive composite electrolyte is preferably clay-like. In this specification, "clay-like" refers to a state in which a material is plastically deformable. 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 material crumbles without deforming when an external force is applied (a cake-like state) is not considered clay-like. The lithium ion conductive composite electrolyte can be controlled to have a clay-like structure by changing the content of the mixed salt in the lithium ion conductive composite electrolyte or by changing the size of the solid content (particularly, the particle size of the sulfide solid electrolyte). As the content of the mixed salt increases and the size of the solid content decreases, the lithium ion conductive composite electrolyte approaches a paste state rather than a clay state.

[0035] The lithium ion conductive composite electrolyte can be produced by appropriately mixing the above-mentioned mixed salt with a sulfide solid electrolyte, although there are no particular limitations thereon. The mixed salt is preferably in a liquid state when mixed. If necessary, the mixed salt may be heated to a temperature above its melting point during mixing.

[0036] <Lithium Secondary Battery> By applying the above-described lithium ion conductive composite electrolyte to the electrolyte layer and / or electrode active material layer of a lithium secondary battery, it is possible to improve the lithium ion conductivity of the lithium secondary battery. That is, according to the present invention, there is also provided a lithium secondary battery including: a composite electrolyte layer containing the lithium ion conductive composite electrolyte; an electrode active material layer containing the lithium ion conductive composite electrolyte, an electrode active material, and a conductive additive; and a lithium secondary battery including battery elements having a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer.

[0037] Hereinafter, an embodiment of a lithium secondary battery according to one aspect of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0038] FIG. 1 is a cross-sectional view schematically illustrating 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") according to one embodiment of the present invention. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular battery element 21, in which charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery outer casing. Here, the battery element 21 has a structure in which a negative electrode, a composite electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 are disposed on the surface of the negative electrode current collector 11'. The positive electrode has a structure in which a positive electrode active material layer 15 are disposed on the surface of a positive electrode current collector 11". As a result, the negative electrode current collector 11', the negative electrode active material layer 13, the composite electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative and positive electrodes) are attached to the negative electrode current collector 11' and the positive electrode current collector 11" respectively, and are configured to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the battery elements 21 by a pressure member (not shown). Therefore, the volume of the battery elements 21 is kept constant.

[0039] The main components of the lithium secondary battery according to this embodiment will be described below.

[0040] [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.

[0041] [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 not particularly limited, but preferably contains the lithium ion conductive composite electrolyte. 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 can constitute the negative electrode without using a negative electrode current collector.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] [Electrolyte Layer] The electrolyte layer is interposed between the negative electrode and the positive electrode and essentially contains an electrolyte. The electrolyte is not particularly limited, but preferably contains the lithium ion conductive composite electrolyte. By using such a configuration, the lithium ion conductivity of the electrolyte layer can be improved.

[0048] When the electrolyte layer is a composite electrolyte layer containing the lithium ion conductive composite electrolyte, it is preferable that the volume of the mixed salt be larger than the volume of voids when the solid content (excluding the mixed salt) contained in the composite electrolyte layer is most densely packed. This configuration allows a sufficient amount of mixed salt to be present in the gaps between particles of the sulfide solid electrolyte, thereby further improving the lithium ion conductivity of the electrolyte layer. In this specification, the "volume of voids when the solid content (excluding the mixed salt) contained in the composite electrolyte layer is most densely packed" is defined as the value obtained by placing the solid content contained in the composite electrolyte layer in a 10 mL glass graduated cylinder, measuring the filling volume after tapping 200 times, and subtracting the solid content volume from the filling volume. The solid content volume can be calculated by multiplying the mass of each component contained in the solid content by the true density.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] [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 not particularly limited, but preferably contains the lithium ion conductive composite electrolyte. 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 can constitute the positive electrode without using a positive electrode current collector.

[0053] 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 LiCoO２ , LiMnO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] [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.

[0059] [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.).

[0060] [Battery Enclosure Material] As the battery enclosure 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 enclosure material because it allows for easy adjustment of the collective pressure applied to the battery element from the outside.

[0061] 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 power source for driving EVs and HEVs.

[0062] <Method of Operating Lithium Secondary Battery> As described above, in a lithium secondary battery, expansion and contraction of the electrode active material due to charge and discharge can cause peeling at the interface between the electrode active material and the sulfide solid electrolyte in the electrode active material layer, or at the interface between the electrode active material and the solid electrolyte at the joint surface between the electrode active material layer and the electrolyte layer, which can result in the disconnection of the lithium ion conduction path between the electrode active material and the sulfide solid electrolyte. Even in such a case, by applying the lithium ion conductive composite electrolyte to the electrolyte layer and / or electrode active material layer of a lithium secondary battery and heating the lithium secondary battery so that the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt, the mixed salt can be melted (liquefied) and the mixed salt can be refilled into the gaps between the electrode active material particles and the sulfide solid electrolyte particles, thereby restoring the lithium ion conduction path. That is, one aspect of the present invention relates to a method for operating a lithium secondary battery including a battery element having a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer described above and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer. The operating method is characterized by including heating the lithium secondary battery so that the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt.

[0063] In the operating method according to this embodiment, the timing of the heating is not particularly limited, but it is preferable to perform the heating when it is determined that the lithium secondary battery has deteriorated based on a predetermined threshold. Examples of the threshold used for the determination include the internal resistance, open circuit voltage, current range, power draw, and operating period of the lithium secondary battery. These thresholds are determined in advance by deterioration tests or simulations.

[0064] In another preferred embodiment, the heating is performed based on the occurrence of interfacial peeling between the electrode active material and the sulfide solid electrolyte. That is, a preferred embodiment of a method for operating a lithium secondary battery further includes determining whether interfacial peeling has occurred between the electrode active material and the sulfide solid electrolyte when charging and / or discharging the lithium secondary battery, and performing the heating when it is determined that interfacial peeling has occurred. The means for determining whether interfacial peeling has occurred is not particularly limited, but examples include a method of calculating the electric double layer capacity based on the amount of change in current value during voltage changes associated with switching between charging and discharging of the battery element, and estimating the increase or decrease in effective interfacial area (the area of ​​the interface between the electrolyte and the electrode active material) relative to the normal state based on the electric double layer capacity. This method will be described with reference to FIGS. 2 and 3 .

[0065] Fig. 2 is a time chart of the voltage and current when switching between charge and discharge. Fig. 3 shows the change in the electric double layer capacity C ｄｌ FIG.

[0066] The current i obtained by detecting the input / output current of the lithium secondary battery is the Faraday current i ｆ and the electric double layer charge / discharge current i ｄｌ (Equation (1)). Therefore, in FIG. 2, the current value is the Faraday current i ｆ and the electric double layer charge / discharge current i ｄｌ The Faraday current i ｆ and the electric double layer charge / discharge current i ｄｌ Since it is not possible to directly detect the values ​​of , the chart in Figure 2 shows estimated values ​​that take into account the characteristics of each.

[0067]

[0068] Voltage E ≒ equilibrium potential E ｅｑ In this case, the Faraday current i ｆ is the overvoltage (i.e., E-E ｅｑ ) (Equation (2)). Note that i ０is the exchange current density, n is the number of reaction electrons (the number of electrons involved in the reaction), F is the Faraday constant, R is the gas constant, and T is the absolute temperature.

[0069]

[0070] On the other hand, the electric double layer charge / discharge current i ｄｌ is proportional to the potential sweep rate v (Equation (3)).

[0071]

[0072] As shown in equation (3), in the case of a three-dimensional electrode, the electric double layer capacitance C ｄｌ is also considered as a function of the potential sweep rate v. This means that when the potential sweep rate v is fast, the calculated electric double layer capacitance C ｄｌ This is because it is considered that v represents the capacitance of a portion of the electrode layer, and that v represents the capacitance of the entire electrode layer when the potential sweep rate v approaches zero. In this embodiment, the determination is made using the capacitance of the entire electrode layer.

[0073] The potential sweep rate v is set in advance, so the electric double layer charge / discharge current i ｄｌ If this is known, the electric double layer capacitance C can be calculated from equation (3). ｄｌ As mentioned above, the current i is the Faraday current i ｆ and the electric double layer charge / discharge current i ｄｌ and the Faraday current i ｆ and the electric double layer charge / discharge current i ｄｌ Although the individual values ​​of i cannot be directly detected, their behavior can be estimated as shown in Figure 2. ｆ and the electric double layer charge / discharge current i ｄｌ When the charge / discharge is switched (that is, when the voltage E is switched between increasing and decreasing), the Faraday current i ｆ does not change, and the electric double layer charge / discharge current i ｄｌ The positive and negative signs of the current i are reversed. Therefore, the change in the current i at this timing is 2i ｄｌ Since the absolute value of this change remains the same but the sign is reversed, halving the change in current i will reduce the electric double layer charge / discharge current i ｄｌThe electric double layer charge / discharge current i ｄｌ From equation (3), the electric double layer capacitance C ｄｌ Calculate.

[0074] FIG. 3 shows the electric double layer capacity C for each potential sweep rate v when two different cell pressures, high and low, are applied to the same lithium secondary battery. ｄｌ The vertical axis represents the electric double layer capacitance C ｄｌ The horizontal axis represents the potential sweep rate v, and black circles represent the case where the cell pressure is high, and white circles represent the case where the cell pressure is low.

[0075] As shown in FIG. 3, the electric double layer capacitance C ｄｌ The difference becomes more significant as the potential sweep rate v becomes larger and as the potential sweep rate v approaches zero. When two different cell pressures, high and low, are applied to the same lithium secondary battery, it can be estimated that the effective interfacial area is larger when the cell pressure is high than when the cell pressure is low.

[0076] Therefore, the electric double layer capacitance C ｄｌ There is a correlation between the electric double layer capacitance and the effective interfacial area. ｄｌ It can be assumed that the larger the effective interfacial area, the larger the electric double layer capacity C of the lithium secondary battery in a normal state. ｄｌ If this is known, the electric double layer capacitance C calculated by the above method can be calculated. ｄｌ By comparing this with the measured value, the increase or decrease in the effective interfacial area can be estimated. If the effective interfacial area decreases, it is determined that interfacial delamination has occurred.

[0077] In the operating method according to this embodiment, the heating means used to heat the lithium secondary battery is not particularly limited as long as it can heat the mixed salt, and various heating means can be used, such as resistance heating, induction heating, dielectric heating, microwave heating, hot air heating, etc. Heating may be performed only on the electrolyte layer containing the lithium ion conductive composite electrolyte and / or the electrode active material layer, or on the entire lithium secondary battery.

[0078] The heating temperature is also not particularly limited as long as it is a temperature at which the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt, and is, for example, 10 to 200°C, preferably 20 to 180°C, more preferably 30 to 170°C, even more preferably 40 to 160°C, still more preferably 50 to 150°C, particularly preferably 60 to 140°C, and most preferably 70 to 130°C.

[0079] Preferably, the operating method according to this embodiment further includes increasing the pressure applied to the lithium secondary battery in the stacking direction when heating the lithium secondary battery. By configuring in this manner, the molten (liquefied) mixed salt is more likely to fill the gap between the electrode active material and the sulfide solid electrolyte, making it possible to regenerate the lithium ion conduction paths more reliably or in a shorter time.

[0080] <Control Device for Lithium Secondary Battery> The present invention also provides a control device for a lithium secondary battery suitable for the method of operating the lithium secondary battery. That is, one aspect of the present invention relates to a control device for a lithium secondary battery including a battery element having a positive electrode having a positive electrode active material layer, a negative electrode having a negative electrode active material layer, and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer described above, and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer described above. The control device is characterized by including an interface peeling detection unit that detects whether interfacial peeling has occurred between the electrode active material and the sulfide solid electrolyte, and a control unit that, when the interface peeling detection unit detects interfacial peeling during charging and / or discharging of the lithium secondary battery, controls heating of the lithium secondary battery so that the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt.

[0081] 4 is a schematic diagram of a control device for a lithium secondary battery according to one embodiment of the present invention. This example illustrates a control device that detects interface peeling by calculating the electric double layer capacity based on the amount of change in current value during voltage changes associated with switching between charging and discharging of the battery elements, and estimating the increase or decrease in effective interfacial area relative to the normal state based on the calculated electric double layer capacity. The control device 30 of this embodiment includes a stacked secondary battery 10a to be controlled, a sensor 31, a temperature sensor 32, an interface peeling detection unit 33, a control unit 35, and a heating unit 37.

[0082] The stacked secondary battery 10a shown in Fig. 4 is similar to that shown in Fig. 1, and at least one of the electrolyte layer, the positive electrode active material layer, and the negative electrode active material layer contains the lithium ion conductive composite electrolyte. The sensor 31 acquires information (input / output current and voltage) for detecting interfacial peeling between the electrode active material and the sulfide solid electrolyte in the stacked secondary battery 10a. The interface peeling detection unit 33 is composed of a microcomputer equipped with a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The interface peeling detection unit 33 calculates the electric double layer capacitance C based on the information (input / output current and voltage) from the sensor 31. ｄｌ and estimates an increase or decrease in the effective interfacial area. Then, based on the increase or decrease in the effective interfacial area, it is detected whether or not interfacial peeling has occurred between the electrode active material and the sulfide solid electrolyte. If interfacial peeling is detected in the interfacial peeling detection unit 33, information about this is sent from the interfacial peeling detection unit 33 to the control unit 35. The control unit 35 is composed of a microcomputer equipped with a CPU, ROM, RAM, and an I / O interface. The control unit 35 controls heating by the heating unit 37 based on information from the interfacial peeling detection unit 33 and the temperature sensor 32. A plurality of temperature sensors 32 are provided to obtain the temperature distribution within the surface of the stacked secondary battery 10a. Note that the control unit 35 may also function as the interfacial peeling detection unit 33.

[0083] The above describes an embodiment of the present invention, but the present invention is not limited to the configurations described in the above embodiment, and can be modified as appropriate based on the claims.

[0084] For example, the type of battery to which the lithium ion conductor according to the present invention can be applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically bonded to one surface of a current collector and a negative electrode active material layer electrically bonded to the opposite surface of the current collector.

[0085] The following embodiments are also included within the scope of the present invention: Item 1: A lithium ion conductive composite electrolyte containing a sulfide solid electrolyte and a mixed salt containing a first anion, a second anion, and lithium ions; Item 2: The lithium ion conductive composite electrolyte according to Item 1, 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 3: 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 are each independently an integer of 0 to 4), the lithium ion conductive composite electrolyte according to Item 1 or 2; Item 4: The lithium ion conductive composite electrolyte according to Item 3, wherein the first anion is a bis(fluorosulfonyl)imide anion in which m = n = 0 in Formula 1; Item 5: The lithium ion conductive composite electrolyte according to Item 3 or 4, wherein at least one of the first anion and the second anion is an asymmetric anion in which m ≠ n in Formula 1; Item 6: The lithium ion conductive composite electrolyte according to any one of Items 1 to 4, wherein the content of the first anion is 20 to 80 mol% with respect to the total number of moles of the first anion and the second anion; Item 7: The lithium ion conductive composite electrolyte according to any one of Items 1 to 6, wherein the mixed salt further contains a third anion and an alkali metal ion (excluding lithium ions); Item 8: The lithium ion conductive composite electrolyte according to Item 7, wherein the alkali metal ion is at least one selected from the group consisting of sodium ions, potassium ions, rubidium ions, and cesium ions; Item 9: The lithium ion conductive composite electrolyte according to Item 7 or 8, wherein the content of the alkali metal ions is more than 0 mol% and not more than 33 mol% relative to the total number of moles of the lithium ions and the alkali metal ions contained in the mixed salt; Item 10: The lithium ion conductive composite electrolyte according to any one of Items 1 to 9, wherein the content is substantially free of organic cations; Item 11: The lithium ion conductive composite electrolyte according to any one of Items 1 to 10, wherein the lithium ion conductive composite electrolyte is clay-like; Item 12: The lithium ion conductive composite electrolyte according to any one of Items 1 to 11, wherein the content of the sulfide solid electrolyte is 11 to 98 mass% relative to 100 mass% of the total mass of the lithium ion conductive composite electrolyte; Item 13: A composite electrolyte layer comprising the lithium ion conductive composite electrolyte according to any one of Items 1 to 12; Item 14: A composite electrolyte layer according to Item 13, wherein the volume of the mixed salt is larger than the volume of voids when the solid content (excluding the mixed salt) contained in the composite electrolyte layer is most densely packed; Item 15: An electrode active material layer comprising the lithium ion conductive composite electrolyte according to any one of Items 1 to 12, an electrode active material, and a conductive assistant;Item 16: A lithium secondary battery comprising a battery element having: a positive electrode having a positive electrode active material layer; a negative electrode having a negative electrode active material layer; and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer according to Item 13 or 14, and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer according to Item 15; Item 17: A lithium secondary battery comprising a battery element having: a positive electrode having a positive electrode active material layer; a negative electrode having a negative electrode active material layer; and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer according to Item 13 or 14, and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer according to Item 15, the method for operating a lithium secondary battery comprising: heating the lithium secondary battery so that the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt; Item 18: The method for operating a lithium secondary battery according to Item 17, further comprising determining whether or not interfacial peeling has occurred between the electrode active material and the sulfide solid electrolyte when performing a charge treatment and / or a discharge treatment of the lithium secondary battery, and performing the heating when it is determined that the interfacial peeling has occurred; Item 19: The method for operating a lithium secondary battery according to Item 17 or 18, further comprising increasing the pressure that pressurizes the lithium secondary battery in the stacking direction when heating the lithium secondary battery;Item 20: A control device for a lithium secondary battery comprising a battery element having: a positive electrode having a positive electrode active material layer; a negative electrode having a negative electrode active material layer; and an electrolyte layer interposed between the positive electrode and the negative electrode, wherein at least one of the electrolyte layers is the composite electrolyte layer according to Item 13 or 14, and / or at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer according to Item 15, the control device including: an interface peeling detection unit that detects whether interfacial peeling has occurred between the electrode active material and the sulfide solid electrolyte; and a control unit that, when the interface peeling detection unit detects interfacial peeling during charging and / or discharging of the lithium secondary battery, controls heating of the lithium secondary battery so that the temperature of the mixed salt is equal to or higher than the melting point of the mixed salt.

[0086] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the 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.

[0087] <Examples of Manufacturing Lithium Ion Conductive Composite Electrolyte> [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 so that the molar ratio of first anion to second anion was 6:4, and placed in a beaker. The 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. This produced a liquid mixed salt (Li([FSA] ０．６ [TFSA] ０．４), melting point 391 K (118° C.). When the liquid mixed salt was stored at room temperature, it maintained a supercooled liquid state for about one month.

[0088] 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 example.

[0089] <Resistance Measurement> [Test Example 1] A stainless steel cylindrical convex punch (13 mm diameter) was inserted into the bottom of a cylindrical tube jig (13 mm diameter) manufactured by Macor, and 200 mg of the lithium ion conductive composite electrolyte was placed on the top of the cylindrical tube jig. Then, another stainless steel cylindrical convex punch was inserted to sandwich the composite electrolyte, and the composite electrolyte was pressed at a pressure of 110 MPa using a uniaxial press to produce a pellet (13 mm diameter, 1 mm thick) made of the composite electrolyte. Next, the upper cylindrical convex punch was removed, and an indium foil (200 μm thick) punched to a diameter of 13 mm was placed on top of it, and the cylindrical convex punch was inserted again. Similarly, the lower cylindrical convex punch was removed, and an indium foil (200 μm thick) punched to a diameter of 13 mm was placed on top of it, and the cylindrical convex punch was inserted again. In this way, a blocking cell of Test Example 1 having a configuration of indium / lithium ion conductive composite electrolyte / indium was produced.

[0090] The resistance (25°C) of the blocking cell was measured by voltage-controlled alternating current impedance spectroscopy (PEIS) using an electrochemical measurement system (VMP-300, manufactured by Biologic) with a voltage amplitude of ±10 mV relative to the open circuit voltage (OCV) of the cell and a frequency range of 1 Hz to 7 MHz.

[0091] [Test Example 2] A blocking cell of Test Example 2 was produced in the same manner as in Test Example 1, except that the pressing pressure applied to the lithium ion conductive composite electrolyte when producing the blocking cell was 220 MPa, and the resistance was measured.

[0092] [Test Example 3] A blocking cell of Test Example 3 was produced in the same manner as in Test Example 1, except that the pressing pressure applied to the lithium ion conductive composite electrolyte when producing the blocking cell was 330 MPa, and the resistance was measured.

[0093] Comparative Test Example 1 Instead of the lithium ion conductive composite electrolyte, a sulfide solid electrolyte (Li ６ P.S. ５ A blocking cell of Comparative Test Example 1 was prepared in the same manner as in Test Example 1, except that a crystalline silicon dioxide (C1, average particle size 1.0 μm) was used, and the resistance was measured.

[0094] Comparative Test Example 2 A blocking cell of Comparative Test Example 2 was produced in the same manner as in Comparative Test Example 1, except that the pressing pressure applied to the lithium ion conductive composite electrolyte when producing the blocking cell was 220 MPa, and the resistance was measured.

[0095] Comparative Test Example 3 A blocking cell of Comparative Test Example 3 was produced in the same manner as in Comparative Test Example 1, except that the pressing pressure applied to the lithium ion conductive composite electrolyte when producing the blocking cell was 330 MPa, and the resistance was measured.

[0096] These results are shown in Figure 5. In the graph shown in Figure 5, the resistance values ​​obtained in Test Examples 1 and 2 are shown as relative values ​​when the resistance value obtained in Test Example 3 is set to 100%, and the resistance values ​​obtained in Comparative Test Examples 1 and 2 are shown as relative values ​​when the resistance value obtained in Comparative Test Example 3 is set to 100%.

[0097] As shown in Figure 5, a comparison of Test Examples 1 and 2 with Comparative Test Examples 1 and 2 reveals that the lithium ion conductive composite electrolyte containing the sulfide solid electrolyte and mixed salt according to the present invention has lower resistance and superior lithium ion conductivity than the sulfide solid electrolyte alone. This is thought to be because, even when voids exist between particles of the sulfide solid electrolyte, lithium ions are able to be conducted between the particles via the mixed salt. There was almost no change in resistance between Test Example 3 and Comparative Test Example 3. This is thought to be because the high pressing pressure prevents voids from forming between particles of the sulfide solid electrolyte.

[0098] This application is based on Japanese Patent Application No. 2024-131945, filed on August 8, 2024, the disclosure of which is hereby incorporated by reference in its entirety.

[0099] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 15 positive electrode active material layer, 17 electrolyte layer, 19 single cell layer, 21 battery element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film, 30 control device, 31 sensor, 32 temperature sensor, 33 interface peeling detection unit, 35 control unit, 37 heating unit.

Claims

a sulfide solid electrolyte; a mixed salt comprising a first anion, a second anion, and a lithium ion; A lithium ion conducting composite electrolyte comprising:

2. The lithium ion conducting composite electrolyte according to claim 1, wherein the melting point of the mixed salt is lower than the melting point of the salt formed from the first anion and lithium ions and the melting point of the salt formed from the second anion and lithium ions. 　 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 lithium ion conductive composite electrolyte according to claim 2, represented by the formula (1): (wherein m and n each independently represent an integer of 0 to 4).

4. The lithium ion conducting composite electrolyte of claim 3, wherein the first anion is a bis(fluorosulfonyl)imide anion in which m=n=0 in Formula 1.

4. The lithium ion conducting composite electrolyte of claim 3, wherein at least one of the first anion and the second anion is an asymmetric anion where m≠n in Formula 1.

5. The lithium ion conductive composite electrolyte according to claim 4, wherein the content of the first anion is 20 to 80 mol % with respect to the total number of moles of the first anion and the second anion.

10. The lithium ion conducting composite electrolyte of claim 1, wherein the mixed salt further comprises a third anion and an alkali metal ion (but excluding lithium ion).

8. The lithium ion conductive composite electrolyte according to claim 7, wherein the content of the alkali metal ions is more than 0 mol % and 33 mol % or less with respect to the total number of moles of the lithium ions and the alkali metal ions contained in the mixed salt.

10. The lithium ion conducting composite electrolyte of claim 1, which is substantially free of organic cations.

10. The lithium ion conducting composite electrolyte of claim 1, which is clayey.

2. The lithium ion conductive composite electrolyte according to claim 1, wherein the content of the sulfide solid electrolyte is 11 to 98 mass% relative to 100 mass% of the total mass of the lithium ion conductive composite electrolyte. 　 A composite electrolyte layer comprising the lithium ion conducting composite electrolyte of claim 1.

13. The composite electrolyte layer according to claim 12, wherein a volume of the mixed salt is larger than a volume of voids when solids contained in the composite electrolyte layer (excluding the mixed salt) are most densely packed. 　 An electrode active material layer comprising the lithium ion conductive composite electrolyte according to claim 1, an electrode active material, and a conductive additive. 　 a positive electrode having a positive electrode active material layer; a negative electrode having a negative electrode active material layer; an electrolyte layer interposed between the positive electrode and the negative electrode; a battery element having At least one of the electrolyte layers is a composite electrolyte layer according to claim 12; and / or A lithium secondary battery, wherein at least one of the positive electrode active material layer and the negative electrode active material layer is the electrode active material layer according to claim 14.

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