Negative electrode intermediate layer for lithium precipitation type secondary battery and lithium precipitation type secondary battery using same

Abstract

The present invention provides a means capable of improving discharge capacity during high-rate discharge, in a lithium precipitation type secondary battery. Provided is a negative electrode intermediate layer for a lithium precipitation type secondary battery, the negative electrode intermediate layer including, as main components, a structural material composed of a material that does not occlude and release lithium, and an electronic conductor that covers at least a part of the surface of the structural material.

Description

Negative electrode intermediate layer for lithium deposition type secondary battery and lithium deposition type secondary battery using the same

[0001] The present invention relates to a negative electrode intermediate layer for a lithium deposition type secondary battery and a lithium deposition type secondary battery using the same.

[0002] In recent years, research and development of all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials primarily composed of ionic conductors capable of ion conduction 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 common in conventional liquid-based lithium secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density.

[0003] One type of all-solid-state lithium secondary battery is known as a lithium deposition type, in which lithium metal is deposited on a negative electrode current collector during charging. While lithium deposition type all-solid-state lithium secondary batteries have excellent energy density and output characteristics, they suffer from the problem of susceptibility to short circuits due to dendrites growing from the lithium metal layer. As a means of suppressing dendrite growth, a technique has been proposed in which a negative electrode active material layer (negative electrode intermediate layer) containing a metal material and a carbon material is provided between the solid electrolyte layer and the negative electrode current collector.

[0004] For example, Japanese Patent Application Laid-Open No. 2022-98487 discloses an anode material including a carbonaceous material and metal particles dispersed within, between, or on the surface of the carbonaceous material. It is believed that providing an anode active material layer (anode intermediate layer) including an anode material having such a configuration in an all-solid-state secondary battery prevents aggregation of the metal particles and enables a uniform current distribution in the anode layer.

[0005] However, according to the investigations of the present inventors, it has been found that lithium deposition type secondary batteries to which the technology described in the above document is applied may not be able to obtain sufficient discharge capacity during high-rate discharge.

[0006] Therefore, an object of the present invention is to provide a means for improving the discharge capacity during high-rate discharge in a lithium deposition type secondary battery.

[0007] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that the above-mentioned problems can be solved by forming a negative electrode intermediate layer using a composite material in which the surface of a structural material made of a material that does not absorb or release lithium is coated with an electron conductor, thereby completing the present invention.

[0008] That is, one embodiment of the present invention is a negative electrode intermediate layer for a lithium deposition-type secondary battery, comprising, as a main component, a structural material made of a material that does not absorb or release lithium, and an electron conductor that coats at least a portion of the surface of the structural material.

[0009] Fig. 1 is an image obtained by observing with a scanning electron microscope (SEM) a cross section of the negative electrode intermediate layer for a lithium deposition-type secondary battery produced in Example 1. Fig. 2 is a cross-sectional view schematically showing the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention.

[0010] <Negative Electrode Intermediate Layer for Lithium Deposition Secondary Battery> One aspect of the present invention is a negative electrode intermediate layer for a lithium deposition secondary battery (hereinafter also simply referred to as "negative electrode intermediate layer"), comprising, as a main component, a structural material composed of a material that does not occlude or release lithium, and an electron conductor coating at least a portion of the surface of the structural material. According to this aspect, by forming a negative electrode intermediate layer using a composite material composed of such a structural material and an electron conductor, it is possible to improve the discharge capacity during high-rate discharge in a lithium deposition secondary battery. The mechanism by which the negative electrode intermediate layer according to this aspect exhibits the above-described effects is not fully understood, and while not bound by any theory, the following mechanism is speculated. The negative electrode material described in the aforementioned Japanese Patent Laid-Open No. 2022-98487 includes a carbon-based material (e.g., carbon black) and metal (e.g., silver) particles dispersed within, between, or on the surface of the carbon-based material. During battery discharge, lithium ions migrate from the lithium metal layer (the negative electrode active material layer in this specification) through the negative electrode intermediate layer to the positive electrode active material layer. Here, the carbon-based material has the property of absorbing and releasing lithium, and at least a portion of the lithium that migrates during discharge can migrate from the negative electrode side to the positive electrode side through the carbon-based material while being absorbed and released by the carbon-based material. Because this lithium migration accompanied by absorption and release is slow, it is thought that this may become rate-limiting during high-rate discharge, resulting in insufficient discharge capacity. Meanwhile, the negative electrode intermediate layer according to this embodiment contains, as its main component, a structural material composed of a material that does not absorb and release lithium, and an electronic conductor coating at least a portion of the surface of the structural material. This structural material forms an appropriate space for lithium deposition in the negative electrode intermediate layer, and reduces (or eliminates) the amount of lithium that migrates accompanied by absorption and release during discharge. Furthermore, the electronic conductor coating the surface of the structural material ensures an electronic conduction path in the negative electrode intermediate layer. As a result, it is presumed that the discharge capacity during high-rate discharge in lithium deposition secondary batteries will be improved.

[0011] FIG. 1 is an image of a cross section of the negative electrode intermediate layer for a lithium deposition-type secondary battery prepared in Example 1, observed with a scanning electron microscope (SEM). In the image of FIG. 1 , the negative electrode intermediate layer is formed on the surface of the negative electrode current collector (stainless steel foil; the gray portion at the bottom of FIG. 1 ). The negative electrode intermediate layer shown in FIG. 1 has a configuration in which the surface of a resin bead (circular gray portion in FIG. 1 ) serving as a structural material is coated with silver (Ag; the white portion covering the outer periphery of the resin bead in FIG. 1 ) serving as an electronic conductor, and the composite material is bound by polyvinylidene fluoride (PVDF; the gray portion between the composite material or between the composite material and the negative electrode current collector). Below, each component constituting the negative electrode intermediate layer will be described.

[0012] [Structural Material] The negative electrode intermediate layer according to this embodiment essentially contains, as a main component, a structural material made of a material that does not absorb or release lithium. The structural material has the main function of securing voids in the negative electrode intermediate layer. In this specification, whether or not a material is a "material that does not absorb or release lithium" is determined by the following method.

[0013] First, 0.01 g of sample A to be identified was weighed out, placed in an SLD sleeve (Φ10), and clamped at both ends with hard Cr-plated SLD pins. The sleeve was pressed at room temperature (25°C) for 1 minute under a pressure of 390 MPa to prepare pellet A made of sample A. ６ P.S. ５0.1 g of Cl was weighed out, and a solid electrolyte pellet was prepared in the same manner as above. A measurement half cell was prepared by sequentially stacking SUS foil as a current collector, pellet A, a solid electrolyte pellet, lithium metal as a counter electrode, and SUS foil as a current collector. A pressure of 3 MPa was applied to the measurement half cell in the stacking direction using a pressure member, while charging and discharging were performed at a constant current of 0.1 mA at a temperature of 60°C. The behavior of the cell voltage during this process was measured, and the reversible capacity [mAh] of pellet A was determined from this behavior. The cutoff voltage differs depending on the type of material, but the points at which the cell voltage sharply increases and decreases were taken as the cutoff voltages during charging and discharging, respectively. The product of the time T (h) from the start of charging to cutoff and the constant charging current of 0.1 [mA], and the product of the time T (h) from the start of discharging to cutoff and the constant charging current of 0.1 [mA], divided by the mass (0.01 g) of Sample A used in the measurement, give the charge capacity and discharge capacity per unit mass [mA / g] of Sample A. After repeating this charge / discharge cycle three times, the value of the next discharge capacity is taken as the reversible capacity, and if this is less than 1 [mA / g], Sample A is considered to be a "material that does not absorb or release lithium."

[0014] The material that does not absorb and release lithium is not particularly limited as long as it satisfies the above definition, but examples thereof include resins (synthetic resins, natural resins), ceramics (oxides (e.g., Al ２ O ３ , SiO ２ , ZrO ２ , TiO ２ Examples include carbides, nitrides, borides, etc. The specific types of resins and ceramics can be selected appropriately by those skilled in the art. Among these materials, resins are preferred. That is, the structural material preferably contains at least one type of resin, and preferably consists of at least one type of resin. Resins have the advantage of being flexible and their structure is less likely to be destroyed by stress changes that occur with the deposition and dissolution of lithium. Resins are also lightweight, which is advantageous in terms of improving energy density.

[0015] The shape of the structural material is not particularly limited as long as it can form voids in the negative electrode intermediate layer, and examples thereof include particles, fibers, porous membranes, etc. Among these shapes, particles are preferred.

[0016] When the structural material is particulate, the average particle diameter of the structural material particles is preferably 0.1 μm or more and 2 μm or less, more preferably 0.3 μm or more and 1.5 μm or less, and even more preferably 0.5 μm or more and 1.2 μm or less. If the average particle diameter is within the above range, sufficient voids can be formed in the negative electrode intermediate layer, and the negative electrode intermediate layer can be made thinner. In this specification, the average particle diameter of the structural material particles is defined as the 50% cumulative diameter (D) of the particle diameters of the particles observed in several to several tens of fields of view when a cross section of a layer containing the particles is observed with a scanning electron microscope (SEM) (the maximum distance between any two points on the outline of the observed particles). ５０ )

[0017] The structural material is also characterized in that it is contained as a major component in the negative electrode intermediate layer. In this specification, whether the structural material is a major component or not is determined by checking whether the ratio (area ratio) of the area of ​​the structural material to the cross-sectional area (including voids) of the negative electrode intermediate layer exceeds 50% when the negative electrode intermediate layer is cut perpendicular to its plane and the cross section is observed, using the method described in the Examples below. If the area ratio of the structural material is less than 50%, the effect of improving the high-rate discharge capacity may not be achieved. The area ratio of the structural material is preferably 60% or more and 90% or less, more preferably 65% ​​or more and 80% or less. If the area ratio is within the above range, sufficient voids can be formed in the negative electrode intermediate layer, and the high-rate discharge capacity can be further improved.

[0018] [Electron Conductor] The electron conductor forms an electron conduction path in the negative electrode intermediate layer by covering at least a portion of the surface of the structure. In this specification, the term "electron conductor" refers to a material that exhibits an electron conductivity of 1 mS / cm or more when measured using a powder resistivity measurement system (manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0019] The electron conductor is not particularly limited as long as it satisfies the above definition, but examples include metals, carbon materials (graphite, carbon black, etc.), conductive polymer materials, etc. Among these materials, metals are preferred from the viewpoint of further improving the discharge capacity at high rates. That is, the electron conductor preferably contains at least one metal, and preferably consists of at least one metal.

[0020] In the negative electrode intermediate layer according to this embodiment, it is preferable to use a combination of metal A (hereinafter simply referred to as "metal A") that does not form an alloy with lithium and metal B (hereinafter simply referred to as "metal B") that can form an alloy with lithium. Metal A contributes to maintaining electronic conductivity, and metal B contributes to improving the wettability of lithium. Therefore, by using these metals in combination, it is possible to further improve the discharge capacity at high rates.

[0021] Here, the metal A that does not alloy with lithium is not particularly limited, but preferably includes at least one selected from the group consisting of titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu) and zirconium (Zr), more preferably includes nickel, and even more preferably is nickel. The metal B that can alloy with lithium is also not particularly limited, but preferably includes at least one selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), indium (In), magnesium (Mg) and zinc (Zn), more preferably includes silver, and even more preferably is silver. By using these materials, the discharge capacity at high rates can be further improved.

[0022] When metal A and metal B are used in combination, the metal coating on the surface of the structural material can be, for example, (1) a structure in which the surface of the structural material is coated with an alloy consisting of metal A and metal B; (2) a structure in which metal A coats a portion of the surface of the structural material and metal B coats another portion; or (3) a structure in which metal A coats the surface of the structural material and metal B coats the surface of metal A. Among these, the structure (3) is preferred. Metal B, which can be alloyed with lithium, alloys with a large amount of lithium during charging to form a metal B-Li alloy. When lithium elutes from the metal B-Li alloy during discharging, metal B remains in islands, and the continuity of metal B is lost, which may interrupt the electron conduction path. In the structure (3), even if the continuity of metal B is lost due to metal B coating the surface of metal A, the continuity of metal A is maintained, so the electron conduction path is maintained even after repeated charge-discharge cycles.

[0023] The electron conductor only needs to cover at least a portion of the surface of the structural material. The ratio (area ratio) of the area of ​​the electron conductor to the cross-sectional area (including voids) of the negative electrode intermediate layer, determined by the method described in the Examples below, is preferably 2% or more and 20% or less, more preferably 3% or more and 18% or less, and even more preferably 4% or more and 15% or less. When the area ratio of the electron conductor is 2% or more, a good electron conduction path can be formed. When the area ratio of the electron conductor is 20% or less, sufficient voids can be secured and the energy density can be improved.

[0024] The method for coating the surface of the structural material with an electron conductor is not particularly limited, and known methods can be appropriately adopted. When the electron conductor is a metal, the surface of the structural material can be coated with the electron conductor by a film formation method such as physical vapor deposition (vacuum vapor deposition, ion plating, sputtering, etc.), chemical vapor deposition, plating (electrolytic plating, electroless plating, etc.). From the viewpoint of uniformity of the coating thickness, coating by plating is preferred.

[0025] [Binder] The negative electrode intermediate layer may contain a binder as needed in addition to the composite material composed of the structural material and the electron conductor. For example, if the structural material is in the form of a porous membrane, a self-supporting membrane can be formed using only the composite material, and therefore a binder is not 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, with tetrafluoroethylene and polyvinylidene fluoride being more preferred. These binders may be used alone or in combination of two or more.

[0026] When the negative electrode intermediate layer contains a binder, the content of the binder is preferably 5 parts by mass or more and 35 parts by mass or less relative to 100 parts by mass of the total mass of the composite material (total mass of the structural material and the electron conductor), from the viewpoint of maintaining the structure and improving the energy density at the same time.

[0027] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1.5 μm to 10 μm, more preferably 2 μm to 7 μm, and even more preferably 4 μm to 6 μm. When the thickness of the negative electrode intermediate layer is 10 μm or less, the path of lithium moving through the negative electrode intermediate layer is not too long, so that the cell resistance can be kept low. Furthermore, when the thickness of the negative electrode intermediate layer is 10 μm or less, the energy density can be improved. When the thickness of the negative electrode intermediate layer is 1.5 μm or more, the strength of the negative electrode intermediate layer can be ensured.

[0028] <Lithium Deposition-Type Secondary Battery> By applying the above-mentioned negative electrode intermediate layer to a lithium deposition-type secondary battery, it is possible to suppress the growth of dendrites and improve the discharge capacity during high-rate discharge. Therefore, according to another aspect of the present invention, there is provided a lithium deposition-type secondary battery (hereinafter also simply referred to as a "secondary battery") including a power generating element including: a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode current collector and from which lithium metal is deposited during charging, a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte, and the above-mentioned negative electrode intermediate layer for a lithium deposition-type secondary battery interposed between the negative electrode current collector and the solid electrolyte layer.

[0029] Hereinafter, an embodiment 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 duplicate explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0030] FIG. 2 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. FIG. 2 shows a cross section of the stacked-type secondary battery during charging. The stacked-type secondary battery 10a shown in FIG. 2 has a structure in which a substantially rectangular power-generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior. The power-generating element 21 has a structure in which a negative electrode, a solid 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 made of lithium metal deposited on the surface of the negative electrode current collector 11′ are stacked. A negative electrode intermediate layer 14 is disposed so as to contact the negative electrode active material layer 13 and the solid electrolyte layer 17, respectively. The positive electrode has a structure in which a positive electrode active material layer 15 is 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 negative electrode intermediate layer 14, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constitute one unit cell layer 19. Therefore, it can be said that the stacked secondary battery 10a shown in FIG. 2 has a structure 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 extend 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 power generating element 21 by a pressure member (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0031] Hereinafter, the main components of the lithium deposition type secondary battery according to this embodiment other than the negative electrode intermediate layer will be described.

[0032] [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 limitations on the material constituting the current collector. For example, metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins, can be used as the material constituting the current collector. There are also no particular limitations on the thickness of the current collector, but an example is 10 to 100 μm.

[0033] [Negative Electrode Active Material Layer] The secondary battery according to this embodiment is a so-called lithium deposition type in which lithium metal 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 is the negative electrode active material layer of the secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. Although the negative electrode active material layer does not need to be present during full discharge, in some cases, a negative electrode active material layer composed of a certain amount of lithium metal may be present during full discharge. Furthermore, the thickness of the negative electrode active material layer (lithium metal layer) during full charge is not particularly limited, but is typically 0.1 to 1000 μm.

[0034] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as a main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any solid electrolyte known in the art can be appropriately used. As an example, 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. ４Examples of sulfide solid electrolytes include sulfide solid electrolytes such as those listed above. These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity and a low bulk modulus, allowing them to follow the volume changes of the electrode active material that accompany charge and discharge. These solid electrolytes may be used alone or in combination of two or more. Of course, solid electrolytes other than those listed above may also be used.

[0035] The content of the solid electrolyte in the solid 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.

[0036] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder that can be used in the solid electrolyte layer is the same as that described above for the negative electrode intermediate layer.

[0037] The thickness of the solid electrolyte layer varies depending on the intended configuration of the secondary battery, but is usually 0.1 μm or more and 1000 μm or less, and preferably 10 μm or more and 40 μm or less.

[0038] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and / or a conductive additive as necessary. The positive electrode active material layer is typically disposed on the surface of a positive electrode current collector as shown in Figure 2. 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.

[0039] 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 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 , LiMnPO４ 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.

[0040] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle diameter (D ５０ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. ５０ The value of can be measured by a laser diffraction scattering method.

[0041] The content of the positive electrode active material is not particularly limited, but from the viewpoint of energy density, it is, for example, 50% by mass or more and 99% by mass or less, preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 99% by mass or less, relative to the total mass of the positive electrode active material layer.

[0042] The positive electrode active material layer may further contain a solid electrolyte, a binder, and / or a conductive additive in addition to the positive electrode active material. Here, the solid electrolyte that can be used in the positive electrode active material layer is the same as that described for the solid electrolyte layer above. The binder that can be used in the positive electrode active material layer is the same as that described for the negative electrode intermediate layer above. Examples of conductive additives include 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.), but are not limited thereto. Furthermore, a conductive additive can also be used in which particulate ceramic materials or resin materials are coated with the above-mentioned metal materials by plating or the like.

[0043] The thickness of the positive electrode active material layer varies depending on the configuration of the intended secondary battery, but is, for example, 0.1 μm or more and 1000 μm or less, preferably 30 μm or more and 300 μm or less, more preferably 50 μm or more and 200 μm or less, and even more preferably 70 μm or more and 150 μm or less.

[0044] [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.

[0045] [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.).

[0046] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element, as shown in FIG. 2, 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 achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable as the exterior material because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0047] The secondary battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a power source for driving EVs and HEVs.

[0048] 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.

[0049] For example, the type of battery to which the negative electrode intermediate layer of this embodiment is 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.

[0050] Furthermore, the secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0051] The following items are also included within the scope of the present invention: Item 1: A negative electrode intermediate layer for a lithium deposition secondary battery, comprising: a structural material composed of a material that does not absorb and release lithium as a main component; and an electron conductor that coats at least a portion of the surface of the structural material; Item 2: The negative electrode intermediate layer for a lithium deposition secondary battery according to Item 1, in which the ratio of the area of ​​the structural material to the cross-sectional area (including voids) of the negative electrode intermediate layer for a lithium deposition secondary battery is 60% to 90% (preferably 65% ​​to 80%); Item 3: The negative electrode intermediate layer for a lithium deposition secondary battery according to Item 1 or 2, in which the material that does not absorb and release lithium includes at least one selected from the group consisting of resins and ceramics (preferably includes at least one resin, more preferably consists of at least one resin); Item 4: The negative electrode intermediate layer for a lithium deposition secondary battery according to any one of Items 1 to 3, in which the structural material is in the form of particles, fibers, or a porous film (preferably particles); Item 5: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of Items 1 to 4, wherein the structural material is in the form of particles and has an average particle size of 0.1 μm to 2 μm (preferably 0.3 μm to 1.5 μm, more preferably 0.5 μm to 1.2 μm); Item 6: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of Items 1 to 5, wherein the electron conductor contains a metal (preferably is a metal); Item 7: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to Item 6, wherein the metal contains a metal A that does not alloy with lithium and a metal B that can alloy with lithium; Item 8: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to Item 7, wherein the metal A contains at least one selected from the group consisting of titanium, chromium, manganese, iron, nickel, copper, and zirconium (preferably contains nickel, more preferably is nickel); Item 9: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to Item 7 or 8, wherein the metal B comprises at least one selected from the group consisting of gold, platinum, palladium, silver, aluminum, bismuth, tin, indium, magnesium, and zinc (preferably comprising silver, more preferably silver); Item 10: (1) An alloy composed of the metal A and the metal B coats the surface of the structural material;(2) A portion of the surface of the structural material is coated with the metal A, and another portion is coated with the metal B; or (3) A surface of the structural material is coated with the metal A, and the surface of the metal A is coated with the metal B (preferably (3) A surface of the structural material is coated with the metal A, and the surface of the metal A is coated with the metal B). The negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of items 7 to 9; Item 11: A negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of items 7 to 10, in which the ratio of the area of ​​the electron conductor to the cross-sectional area (including voids) of the negative electrode intermediate layer for a lithium deposition-type secondary battery is 2% or more and 20% or less (preferably 3% or more and 18% or less, more preferably 4% or more and 15% or less); Item 12: Further comprising a binder, Item 13: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of Items 1 to 11, wherein the binder comprises at least one selected from 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) (preferably at least one selected from SBR, PTFE, and PVDF, more preferably at least one selected from PTFE and PVDF); Item 13: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to Item 12, wherein the content of the binder is 10 parts by mass or more and 35 parts by mass or less with respect to 100 parts by mass of the total mass of the structural material and the electron conductor; Item 14: The negative electrode intermediate layer for a lithium deposition-type secondary battery according to any one of Items 1 to 13, wherein the thickness is 1.5 μm or more and 10 μm or less (preferably 2 μm or more and 7 μm or less, more preferably 4 μm or more and 6 μm or less); Item 15: A lithium deposition secondary battery comprising a power generating element including: a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a negative electrode intermediate layer for a lithium deposition secondary battery according to any one of Items 1 to 14, interposed between the negative electrode current collector and the solid electrolyte layer.

[0052] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0053] <Examples of Preparation of Evaluation Cells> [Example 1] (Preparation of Composite Material) The surfaces of resin beads (Micropearl (registered trademark), manufactured by Sekisui Chemical Co., Ltd.; average particle size 1 μm, composed of a cross-linked polymer whose main component is divinylbenzene; the same applies hereinafter) serving as a structural material were coated with silver as an electron conductor by electroless plating to prepare silver-plated resin beads (plating thickness 30 nm).

[0054] (Preparation of Negative Electrode Intermediate Layer) 86 parts by mass of the composite material prepared above, 14 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersion medium were mixed to prepare a negative electrode intermediate layer slurry. The negative electrode intermediate layer slurry was applied to the surface of a stainless steel foil as a negative electrode current collector and dried to obtain a negative electrode intermediate layer (thickness 5 μm).

[0055] (Preparation of Evaluation Cell) The preparation of the evaluation cell was carried out in a glove box in an argon atmosphere with a dew point of −68° C. or less. A stainless steel cylindrical convex punch (10 mm diameter) was inserted into one side of a cylindrical tube jig (manufactured by Macor) (tube inner diameter 10 mm, outer diameter 23 mm, height 20 mm), and an argyrodite-type sulfide solid electrolyte (manufactured by Ampcera, Li ６ P.S. ５80 mg of HCl was placed inside. Then, another stainless steel cylindrical convex punch was inserted to sandwich the solid electrolyte, and a hydraulic press was used to press the solid electrolyte at a pressure of 75 MPa for 3 minutes to form a solid electrolyte layer with a diameter of 10 mm and a thickness of 0.6 mm in the cylindrical tube jig. Next, the cylindrical convex punch (which also serves as a positive electrode current collector) inserted from above was temporarily removed, and indium foil (manufactured by Nilaco Corporation, thickness 0.02 mm, diameter 10 mm) was placed on one side of the solid electrolyte layer in the cylindrical tube, and the cylindrical convex punch was inserted again from above. Subsequently, the cylindrical convex punch (which also serves as a negative electrode current collector) inserted from below was temporarily removed, and the negative electrode intermediate layer formed on the stainless steel foil prepared above was inserted on the other side of the solid electrolyte layer in the cylindrical tube so that the exposed surface of the negative electrode intermediate layer faced the solid electrolyte layer, and the cylindrical convex punch was inserted again from below. The indium foil and the negative electrode intermediate layer were pressed to the solid electrolyte layer by pressing at a pressure of 300 MPa for 3 minutes. The upper cylindrical convex punch was removed again, and a lithium foil (manufactured by Nilaco Corporation, thickness 0.20 mm, diameter 8 mm) and an indium foil (manufactured by Nilaco Corporation, thickness 0.30 mm, diameter 9 mm) were placed on top of the indium foil. The cylindrical convex punch was then inserted again, and the mixture was pressed at a pressure of 100 MPa for 3 minutes to form a lithium-indium positive electrode. In this way, an evaluation cell (lithium deposition-type all-solid-state secondary battery) was produced in which the positive electrode current collector, the lithium-indium positive electrode, the solid electrolyte layer, the negative electrode intermediate layer, and the negative electrode current collector were stacked.

[0056] [Example 2] The above (production of a composite material) was carried out by the following method: The surface of resin beads as a structural material was coated with nickel as an electron conductor by electroless plating to produce nickel-plated resin beads (plating thickness: 18 nm); except for this, an evaluation cell for this example was obtained by the same method as in Example 1.

[0057] [Example 3] The above (production of a composite material) was carried out by the following method: the surface of silica beads (average particle size 1.5 μm, the same applies below) as a structural material was coated with nickel as an electron conductor by electroless plating to produce nickel-plated silica beads (plating thickness 14 nm); except for this, an evaluation cell for this example was obtained by the same method as in Example 1.

[0058] [Example 4] The above (production of a composite material) was carried out by the following method; the surface of resin beads as a structural material was coated with nickel as an electron conductor by electroless plating, and then coated with silver as an electron conductor by electroless plating to produce nickel / silver-plated resin beads (nickel plating thickness: 19 nm, silver plating thickness: 23 nm); except for this, an evaluation cell for this example was obtained by the same method as in Example 1.

[0059] [Example 5] The above (production of a composite material) was carried out by the following method; the surface of silica beads as a structural material was coated with nickel as an electron conductor by electroless plating, and then coated with silver as an electron conductor by electroless plating to produce nickel / silver-plated silica beads (nickel plating thickness: 11 nm, silver plating thickness: 26 nm); except for this, an evaluation cell for this example was obtained by the same method as in Example 1.

[0060] Comparative Example 1 The above (production of the negative electrode intermediate layer) was carried out by the following method: 64.5 parts by mass of amorphous carbon particles (DENKA BLACK (registered trademark) Li-400, manufactured by Denka Company, average particle diameter 48 nm, hereinafter the same) and 21.5 parts by mass of silver particles (particle diameter 40 to 60 nm, hereinafter the same) were mixed using a mortar. 86 parts by mass of the resulting mixture was mixed with 14 parts by mass of polyvinylidene fluoride (PVDF) as a binder and an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersion medium to prepare a negative electrode intermediate layer slurry. The negative electrode intermediate layer slurry was applied to the surface of a stainless steel foil as a negative electrode current collector and dried to obtain a negative electrode intermediate layer (thickness 5 μm).

[0061] Except for this, the same method as in Example 1 was used to obtain an evaluation cell for this comparative example.

[0062] Comparative Example 2 An evaluation cell for this comparative example was obtained in the same manner as in Comparative Example 1, except that in the above (preparation of the negative electrode intermediate layer), the amount of amorphous carbon particles was changed from 64.5 parts by mass to 43 parts by mass, and the amount of silver particles was changed from 21.5 parts by mass to 43 parts by mass.

[0063] [Comparative Example 3] The above (preparation of composite material) was carried out in accordance with the method described in Production Example 1 of JP 2022-98487 A by the following method: 50 mL of glycerol (99.9%, manufactured by Aldrich) and 0.5 mM polyvinylpyrrolidone (PVP) (Mw = 55,000, manufactured by Aldrich) were placed in a 100 mL reaction vessel, heated to 80 ° C., mixed until a transparent solution was obtained, and then cooled to 30 ° C. Next, 5 g of amorphous carbon particles were added to the mixture, mixed for 10 minutes, and 50 mM AgNO was added. ３ (99.9%, manufactured by Aldrich) was added and mixed for 5 minutes. The temperature of the mixture was raised to 100°C and allowed to react for 12 hours. 50 mL of deionized water was added and ultrasonic treatment was performed for 2 minutes. Next, glycerol and polyvinylpyrrolidone were separated from the supported carbon using a glass filter, and the silver-supported amorphous carbon particles were washed with ethanol and deionized water to remove any remaining components. After washing, the particles were dried in a vacuum oven at 90°C for at least 8 hours to obtain a silver-carbon composite. The silver content in the silver-carbon composite was 30% by mass and the carbon content was 70% by mass. The evaluation cell for this example was obtained using the same method as in Example 1, except for this.

[0064] <Proportion (area ratio) of structural material in negative electrode intermediate layer> The negative electrode intermediate layer (before charge / discharge reaction) prepared above was cut perpendicular to its plane, and the cross section was observed using a scanning electron microscope (SEM; magnification: 10,000 times). From the observed image, the area A of the cross section of the negative electrode intermediate layer (the area surrounded by the outer edge of the negative electrode intermediate layer, including voids) and the total area B of the structural material included in the image were calculated, and the proportion (area ratio) of the structural material in the negative electrode intermediate layer was calculated using the formula: B ÷ A × 100 (%). The obtained values ​​are shown in Table 1 below. In this specification, when the proportion (area ratio) exceeds 50%, it is considered that the structural material is present as the main component in the negative electrode intermediate layer.

[0065] <Proportion (area ratio) of electronic conductor in negative electrode intermediate layer> The negative electrode intermediate layer (before charge / discharge reaction) prepared above was cut perpendicular to its plane, and the cross section was observed using a scanning electron microscope (SEM; magnification: 10,000 times). From the observed image, the area A of the cross section of the negative electrode intermediate layer (the area surrounded by the outer edge of the negative electrode intermediate layer, including voids) and the total area C of the electronic conductor contained in the image were determined, and the proportion (area ratio) of the electronic conductor in the negative electrode intermediate layer was calculated using the formula: C ÷ A × 100 (%). The obtained values ​​are shown in Table 1 below.

[0066] <Rapid Discharge Characteristics of Cell> The rapid discharge characteristics of the evaluation cell prepared above were evaluated using a charge / discharge tester (HJ-SD8, manufactured by Hokuto Denko Corporation). First, the cell was placed in a constant temperature bath set at 60°C. After the cell temperature became constant, a current of 0.2 mA / cm was applied. ２ The battery was subjected to constant current charging (lithium deposition reaction) for 20 hours at a current density of 0.2 mA / cm. Thereafter, the battery was subjected to constant current discharging (lithium elution reaction) at the same current density until the cell voltage reached 1.4 V. This charge / discharge cycle was repeated three times to carry out pretreatment. ２ After 20 hours of constant current charging at a current density of 0.4 mA / cm ２ The capacity when constant current discharge was performed at a current density of 1.4 V to a cell voltage of 1.4 V was defined as the low rate discharge capacity C Ｌ Subsequently, the current was set to 0.2 mA / cm ２ After 20 hours of constant current charging at a current density of 8.0 mA / cm ２ The capacity when constant current discharge was performed at a current density of 1.4 V to a cell voltage of 1.4 V was defined as the high rate discharge capacity C Ｈ The ratio of the high-rate discharge capacity to the low-rate discharge capacity was calculated using the formula: C Ｈ ÷C Ｌ The rapid discharge capacity retention rate (%) was calculated by multiplying the ratio by 100 (%). The results are shown in Table 1 below.

[0067]

[0068] As shown in Table 1, according to the present invention, by constructing a lithium deposition type secondary battery using a negative electrode intermediate layer containing a composite material in which an electron conductor is coated on the surface of a structural material made of a material that does not absorb and release lithium, it is understood that the discharge capacity during high-rate discharge is improved.

[0069] A comparison of Examples 1 and 2 with Example 4, or a comparison of Example 3 with Example 5, reveals that the discharge capacity during high-rate discharge is further improved by using, as an electron conductor, a metal A that does not alloy with lithium and a metal B that can alloy with lithium in combination.

[0070] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layer, 21 power generating element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film.

Claims

A structural material mainly composed of a material that does not absorb or release lithium, an electron conductor covering at least a portion of the surface of the structural material; A negative electrode intermediate layer for a lithium deposition type secondary battery, comprising:

2. The negative electrode intermediate layer for a lithium deposition-type secondary battery according to claim 1, wherein the electron conductor is a metal.

3. The negative electrode intermediate layer for a lithium deposition-type secondary battery according to claim 2, wherein the metals include a metal A that does not form an alloy with lithium and a metal B that can form an alloy with lithium.

4. The negative electrode intermediate layer for a lithium deposition type secondary battery according to claim 3, wherein the metal A comprises at least one selected from the group consisting of titanium, chromium, manganese, iron, nickel, copper, and zirconium.

4. The negative electrode intermediate layer for a lithium deposition-type secondary battery according to claim 3, wherein the metal B comprises at least one selected from the group consisting of gold, platinum, palladium, silver, aluminum, bismuth, tin, indium, magnesium, and zinc.

3. The negative electrode intermediate layer for a lithium deposition-type secondary battery according to claim 1, wherein the structural material comprises at least one resin. 　 a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode current collector and on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; the negative electrode intermediate layer for a lithium deposition secondary battery according to claim 1 or 2, which is interposed between the negative electrode current collector and the solid electrolyte layer; A lithium deposition type secondary battery comprising a power generating element having the above structure.

Images