Energy storage element, method for manufacturing an energy storage element, and energy storage device

Abstract

A power storage element according to one aspect of the present invention comprises a non-aqueous electrolyte and an electrode body that includes a positive electrode, a negative electrode and a separator. The negative electrode includes: a negative electrode base material; a first layer which is disposed directly or indirectly on the separator side of the negative electrode base material and which contains gold, platinum or a metal that is a combination of these; and a second layer which is disposed on the separator side of the first layer, contains a lithium salt and a polymer having lithium ion conductivity, and can restrict passage of the non-aqueous electrolyte. The negative electrode further contains a lithium metal layer that is disposed between the negative electrode base material and the first layer.

Description

[Technical Field]

[0001] The present invention relates to an energy storage element, a method for manufacturing an energy storage element, and an energy storage device. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as energy storage elements.

[0003] In recent years, there has been a demand for higher capacity negative electrodes in order to increase the capacity of non-aqueous electrolyte secondary batteries. Compared to graphite, which is currently widely used as a negative electrode active material in lithium-ion secondary batteries, lithium metal has a significantly larger theoretical capacity per unit mass of active material. That is, the theoretical capacity per unit mass of graphite is 372 mAh / g, while the theoretical capacity per unit mass of lithium metal is 3860 mAh / g, which is significantly larger. For this reason, non-aqueous electrolyte secondary batteries using lithium metal as a negative electrode active material have been proposed (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-124154 [Overview of the project] [Problems that the invention aims to solve]

[0005] In energy storage elements using lithium metal as the negative electrode active material as described above, lithium metal may deposit in a dendritic pattern on the negative electrode surface during charging (hereinafter, lithium metal in a dendritic form will be referred to as "dendrites"). If these dendrites grow toward the separator, they may penetrate the separator and come into contact with the positive electrode, potentially causing a short circuit or other problems.

[0006] The object of the present invention is to provide an energy storage element in which the growth of dendrites toward the separator side is suppressed, a method for manufacturing the same, and an energy storage device equipped with this energy storage element. [Means for solving the problem]

[0007] An energy storage element according to one aspect of the present invention comprises an electrode body including a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode substrate, a first layer disposed directly or indirectly on the separator side of the negative electrode substrate and containing a metal such as gold, platinum, or a combination thereof, and a second layer disposed on the separator side of the first layer and containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and the negative electrode further includes a lithium metal layer disposed between the negative electrode substrate and the first layer.

[0008] A method for manufacturing an energy storage element according to another aspect of the present invention comprises preparing a positive electrode, preparing a separator, preparing a negative electrode, and creating an electrode body by stacking the positive electrode, the separator, and the negative electrode in this order, wherein the preparation of the negative electrode involves forming a first layer containing gold, platinum, or a combination thereof directly or indirectly on the separator side of the negative electrode substrate, forming a second layer on the separator side of the first layer containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and forming a lithium metal layer between the negative electrode substrate and the first layer.

[0009] The power storage device according to another aspect of the present invention includes the one or more power storage elements and a restraining member that restrains the one or more power storage elements, and the one or more power storage elements are pressed in the thickness direction by the restraint by the restraining member, so that the electrode body is in a pressed state.

Advantages of the Invention

[0010] The power storage element according to one aspect of the present invention suppresses the growth toward the separator side of dendrites.

[0011] The method for manufacturing a power storage element according to another aspect of the present invention can manufacture a power storage element in which the growth toward the separator side of dendrites is suppressed.

[0012] The power storage device according to another aspect of the present invention suppresses the growth toward the separator side of dendrites in the power storage element.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a side cross-sectional view schematically showing the layer configuration of an electrode body of an embodiment of a power storage element. [Figure 2] FIG. 2 is a side cross-sectional view schematically showing the layer configuration of an electrode body of another embodiment of a power storage element. [Figure 3] FIG. 3 is a perspective view showing an embodiment of a power storage element. [Figure 4] FIG. 4 is a schematic view showing an embodiment of a power storage device configured by assembling a plurality of power storage elements. [Figure 5] FIG. 5 is a FE-SEM image showing the crystal shape of lithium metal deposited on the first layer containing gold in the negative electrode. [Figure 6] FIG. 6 is a FE-SEM image showing the crystal shape of lithium metal deposited on the second lithium metal layer in the negative electrode without the first layer.

Embodiments for Carrying Out the Invention

[0014] First, an overview of the energy storage element, the method for manufacturing the energy storage element, and the energy storage device disclosed herein will be described.

[0015] Section 1. An energy storage element according to one embodiment of the present invention comprises an electrode body including a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode substrate, a first layer disposed directly or indirectly on the separator side of the negative electrode substrate and containing a metal such as gold, platinum, or a combination thereof, and a second layer disposed on the separator side of the first layer and containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and the negative electrode further includes a lithium metal layer disposed between the negative electrode substrate and the first layer.

[0016] According to the energy storage element described in item 1 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0017] Section 2. The energy storage element described in item 1 above may be formed from a polymer material in which the polymer contained in the second layer contains vinylene carbonate, acrylonitrile, or a combination thereof as monomers.

[0018] According to the energy storage element described in item 2 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0019] Section 3. The energy storage element described in item 1 or 2 above may further include a lithium metal layer disposed between the first layer and the separator as the negative electrode.

[0020] According to the energy storage element described in item 3 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0021] Section 4. The energy storage element described in any one of the above items 1 to 3 may have a separator comprising a base material layer and an inorganic material layer disposed on the negative electrode side of the base material layer.

[0022] According to the energy storage element described in item 4 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0023] Section 5. The energy storage element described in any one of the above paragraphs 1 to 4 may be one in which the lithium salt is lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, or a combination thereof.

[0024] According to the energy storage element described in item 5 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0025] Section 6. The energy storage element described in any one of the above paragraphs 1 to 5 may be in a state in which the electrode body is pressed in the thickness direction.

[0026] According to the energy storage element described in item 6 above, the growth of dendrites toward the separator side in the energy storage element can be suppressed.

[0027] Section 7. A method for manufacturing an energy storage element according to one embodiment of the present invention comprises preparing a positive electrode, preparing a separator, preparing a negative electrode, and manufacturing an electrode body by stacking the positive electrode, the separator, and the negative electrode in this order, wherein the preparation of the negative electrode comprises forming a first layer containing gold, platinum, or a combination thereof directly or indirectly on the separator side of the negative electrode substrate, forming a second layer on the separator side of the first layer containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and forming a lithium metal layer between the negative electrode substrate and the first layer.

[0028] According to the method for manufacturing an energy storage element described in item 7 above, the above-mentioned energy storage element can be manufactured. That is, an energy storage element in which dendrite growth is suppressed can be manufactured.

[0029] Section 8. An energy storage device according to one embodiment of the present invention comprises one or more energy storage elements as described in any one of items 1 to 6 above, and a restraining member that restrains the one or more energy storage elements, wherein the one or more energy storage elements are pressed in the thickness direction of the electrode body by the restraining member, and the electrode body is in a pressed state.

[0030] According to the energy storage device described in item 8 above, the growth of dendrites toward the separator side in the energy storage device can be suppressed.

[0031] An energy storage element according to one aspect of the present invention comprises an electrode body including a positive electrode, a negative electrode, and a separator, and a non-aqueous electrolyte, wherein the negative electrode includes a negative electrode substrate, a first layer disposed directly or indirectly on the separator side of the negative electrode substrate and containing a metal such as gold, platinum, or a combination thereof, and a second layer disposed on the separator side of the first layer and containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and the negative electrode further includes a lithium metal layer disposed between the negative electrode substrate and the first layer.

[0032] Here, "restricting the passage of non-aqueous electrolytes" means completely preventing the passage of non-aqueous electrolytes. Specifically, the swelling amount (absorption amount) of non-aqueous electrolytes in the second layer is 0.25 cm per gram of the second layer under conditions of 25°C and atmospheric pressure. 3 (0.25cm 3 This means that the amount is less than or equal to / g. The second layer mentioned above is not a layer formed by decomposition products of the non-aqueous electrolyte during charging of the energy storage element, but rather a layer formed from the initial state before charging, i.e., a layer formed during the manufacturing of the energy storage element.

[0033] In this energy storage element, the negative electrode is equipped with the first and second layers described above, which suppresses the growth of dendrites toward the separator side (hereinafter also simply referred to as "dendrite growth"). The reason why dendrite growth is suppressed in this way is not entirely clear, but it can be inferred, for example, as follows.

[0034] In other words, the presence of the second layer on the separator side of the first layer suppresses the non-aqueous electrolyte from reaching the first layer, while lithium ions in the second layer and the non-aqueous electrolyte swollen in the second layer can reach the first layer. Thus, direct contact between the non-aqueous electrolyte and the first layer is reduced (blocking effect of the non-aqueous electrolyte), while lithium ions in the second layer and the non-aqueous electrolyte swollen in the second layer can come into contact with the first layer.

[0035] In this energy storage element, during charging, lithium ions from the second layer and the non-aqueous electrolyte swollen in the second layer reach the separator-side surface of the first layer, causing lithium metal crystals to precipitate between the first and second layers. At this time, because the first layer has conductivity due to the gold, platinum, or combination thereof, localized current concentration on the separator-side surface of the first layer is suppressed, making it easier for lithium metal crystals to form relatively uniformly across the entire surface, while making it difficult for localized lithium metal crystals to form on the surface. Therefore, dendrite growth is suppressed. Furthermore, because the first layer contains gold, platinum, or combination thereof, the affinity between the first layer and lithium metal is high. As a result, the lithium metal crystals formed between the first and second layers are more easily formed uniformly across the entire surface of the separator side of the first layer, and particulate lithium metal crystals are more easily formed in a relatively dense state, thus making it easier for the layer of particulate lithium metal crystals to grow into a smoother layer. In addition, the affinity between the first and second layers is also improved, so when forming the second layer on the first layer, the second layer is more easily formed uniformly on the first layer, thereby improving the adhesion of the second layer to the first layer, the uniformity of the thickness of the second layer, and the smoothness of the second layer. As a result, the formation of localized lithium metal crystals can be further suppressed. Therefore, the growth of dendrites is further suppressed.

[0036] When lithium metal crystals are formed relatively uniformly across the entire surface, particulate lithium metal crystals are more likely to form in a relatively dense state. As a result, the particulate lithium metal crystals between the first and second layers tend to grow into a smooth layer with relatively few irregularities and a relatively uniform thickness. On the other hand, in addition to the suppression of dendrite growth by the gold, platinum, or combination thereof as described above, the localized concentration of current is also suppressed by the non-aqueous electrolyte barrier effect of the second layer as described above. This also suppresses dendrite growth caused by direct contact between the non-aqueous electrolyte and the first layer.

[0037] Thus, by having a first and second layer in the negative electrode, the first and second layers cooperate to suppress dendrite growth, while a relatively dense and smooth layer of lithium metal crystals can be formed between the first and second layers. Because this smooth layer of lithium metal crystals has a smaller contact area with the non-aqueous electrolyte compared to a non-smooth layer of lithium metal crystals, dendrite growth is suppressed.

[0038] Furthermore, because the second layer contains the polymer, it is flexible and can expand and contract to conform to the crystal shape of the lithium metal precipitated between the first and second layers. This expansion and contraction suppresses the occurrence of cracks in the second layer due to the crystal growth of the lithium metal, thereby preventing the non-aqueous electrolyte from reaching the first layer through the cracks in the second layer and suppressing the growth of dendrites caused by localized lithium metal crystal formation at the point of arrival.

[0039] Furthermore, the inclusion of a lithium salt in the second layer enhances its flexibility, thereby further suppressing cracking and other damage to the second layer. This further inhibits dendrite growth. In addition, the inclusion of a lithium salt in the second layer improves its lithium ion conductivity, thereby further suppressing localized current concentration. This also further inhibits dendrite growth.

[0040] In addition, the negative electrode further includes a lithium metal layer disposed between the negative electrode substrate and the first layer, so that this lithium metal layer functions as a negative electrode active material layer or a lithium metal replenishment layer. Therefore, the lithium metal layer contributes to charging and discharging as a negative electrode active material layer and can also replenish the amount of electricity corresponding to the lithium metal that can no longer contribute to charging and discharging due to the electrical isolation of the dendrites. Furthermore, the presence of this lithium metal layer causes the lithium metal contained in this layer to alloy with the metal contained in the first layer, making the layer of lithium metal crystals deposited on the first layer a smoother layer and suppressing the growth of dendrites.

[0041] Thus, it is presumed that the growth of dendrites is suppressed by this energy storage element.

[0042] As described above, suppressing dendrite growth reduces the occurrence of short circuits caused by dendrites. Furthermore, suppressing dendrite growth also reduces the electrical isolation of dendrites (formation of dead lithium) that occurs when dendrites detach from the layer of particulate lithium metal crystals formed between the first and second layers during charging. This suppresses the decrease in capacity caused by dead lithium, and consequently, the decrease in discharge capacity maintenance rate is also suppressed. In addition, as described above, while reducing dendrite growth, the layer of particulate lithium metal crystals can be formed, allowing the deposited lithium metal crystals to be effectively utilized as an active material.

[0043] Here, the second layer may be formed from a polymer material containing vinylene carbonate, acrylonitrile, or a combination thereof as monomers.

[0044] If the second layer is formed of a polymer material that readily swells non-aqueous electrolytes, the non-aqueous electrolyte swollen in the second layer can pass through to the first layer, potentially causing localized current concentration due to direct contact between the non-aqueous electrolyte and the first layer. However, if the second layer is formed of a polymer material containing vinylene carbonate, acrylonitrile, or a combination thereof as monomers, the second layer is relatively less prone to swelling non-aqueous electrolytes, thus further reducing direct contact between the non-aqueous electrolyte and the first layer. Consequently, dendrite growth is further suppressed. This further suppression of dendrite growth reduces the occurrence of short circuits caused by dendrites. In addition, further suppression of dendrite growth also reduces the electrical isolation of dendrites (formation of dead lithium), thus further suppressing the decrease in capacity caused by dead lithium, and consequently, the decrease in discharge capacity maintenance rate is also further suppressed.

[0045] Here, the negative electrode may further include a lithium metal layer disposed between the first layer and the separator.

[0046] As mentioned above, although reduced, grown dendrites may become electrically isolated (generate dead lithium) and therefore unable to contribute to charging and discharging. However, if the negative electrode includes a lithium metal layer between the first layer and the separator, this lithium metal layer functions as a negative electrode active material layer or a lithium metal replenishment layer. Therefore, the lithium metal layer contributes to charging and discharging as a negative electrode active material layer and can also replenish the amount of electricity equivalent to the lithium metal that has become unable to contribute to charging and discharging due to the electrical isolation (generate dead lithium) of the dendrites.

[0047] Here, the separator may have a base layer and an inorganic material layer disposed on the negative electrode side of the base layer.

[0048] Thus, when the separator has the inorganic material layer, the presence of this inorganic material layer further hinders the growth of deposited lithium metal toward the separator. In addition, the presence of the inorganic material layer further suppresses penetration of the separator by the lithium metal, thus further suppressing the occurrence of short circuits.

[0049] Here, the lithium salt may be lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, or a combination thereof.

[0050] Thus, when the lithium salt is the compound described above, the flexibility of the second layer can be further increased, thereby further suppressing cracking of the second layer. This further suppresses the growth of dendrites.

[0051] In this case, the electrode body may be in a state where it is pressed in the thickness direction.

[0052] When the electrode body is pressed in the thickness direction as described above, it tends to be more prone to short circuits compared to when it is not pressed. However, even in this prone state, the occurrence of short circuits is suppressed. Therefore, when the electrode body is pressed in the thickness direction, the effect of suppressing the growth of dendrites in the energy storage element is particularly fully demonstrated.

[0053] A method for manufacturing an energy storage element according to another aspect of the present invention comprises preparing a positive electrode, preparing a separator, preparing a negative electrode, and creating an electrode body by stacking the positive electrode, the separator, and the negative electrode in this order, wherein the preparation of the negative electrode involves forming a first layer containing gold, platinum, or a combination thereof directly or indirectly on the separator side of the negative electrode substrate, forming a second layer on the separator side of the first layer containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and forming a lithium metal layer between the negative electrode substrate and the first layer.

[0054] According to this method for manufacturing energy storage elements, the aforementioned energy storage elements can be manufactured. In other words, it is possible to manufacture energy storage elements in which dendrite growth is suppressed.

[0055] Another aspect of the present invention relates to a power storage device comprising one or more power storage elements and a restraining member that restrains the one or more power storage elements, wherein the one or more power storage elements are pressed in the thickness direction of the electrode body by the restraining member, resulting in the electrode body being in a pressed state.

[0056] Because such an energy storage device is equipped with the energy storage element, the growth of dendrites is suppressed. In addition, since the energy storage element is pressed against the electrode body in the thickness direction, the electrode body is pressed in that thickness direction, and as described above, although it is in a state where short circuits are relatively likely to occur, the occurrence of short circuits is suppressed.

[0057] This document describes in detail an energy storage element, the configuration of an energy storage device, a method for manufacturing the energy storage element, and other embodiments related to one embodiment of the present invention. Note that the names of the components (parts) used in each embodiment may differ from the names of the components (parts) used in the background art.

[0058] <Configuration of energy storage element> An energy storage element according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator; a non-aqueous electrolyte; and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. As an example of an energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described.

[0059] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0060] The positive electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 7 The determination is made using Ω·cm as the threshold. The positive electrode substrate material can be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0061] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the secondary battery. "Average thickness of the positive electrode substrate" refers to the value obtained by dividing the punched mass when punching out a predetermined area of ​​the positive electrode substrate by the true density of the positive electrode substrate and the punched area.

[0062] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and for example, it contains a binder and a conductive agent.

[0063] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder (adhesive), a thickener, and a filler as required.

[0064] The positive electrode active material can be appropriately selected from known positive electrode active materials. Usually, a material capable of occluding and releasing lithium ions is used as the positive electrode active material. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include, for example, Li[Li x Ni (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Co (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Co (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Mn (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Ni γ Mn β Co (1-x-γ-β) O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), Li[Li x Ni γ Co β Al (1-x-γ-β) O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), etc. Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li<​​​​​(2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0065] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0066] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0067] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0068] The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

[0069] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

[0070] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0071] The binder content in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the active material can be stably maintained.

[0072] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0073] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0074] The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0075] (Negative electrode) The negative electrode includes a negative electrode substrate, a first layer directly or indirectly disposed on the negative electrode substrate and containing a metal such as gold, platinum, or a combination thereof (hereinafter also referred to as "non-lithium metal"), a second layer disposed on the separator side of the first layer and containing a lithium-ion conductive polymer (hereinafter also referred to as "lithium-ion conductive polymer"), and capable of restricting the passage of the non-aqueous electrolyte, and a lithium metal layer disposed between the negative electrode substrate and the first layer.

[0076] The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and lithium, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. When the negative electrode substrate is made of lithium metal or a lithium alloy, this lithium metal or alloy also constitutes the negative electrode active material or lithium metal layer. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0077] For example, when the material of the negative electrode substrate is copper, nickel, stainless steel, nickel-plated steel or an alloy thereof, or a carbon material, the average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per unit volume of the secondary battery. For example, when the material of the negative electrode substrate is lithium metal or lithium alloy, its average thickness may be set appropriately considering the performance required as a negative electrode active material. In this case, the average thickness of the negative electrode substrate may be set to more than 0 μm and 100 μm or less. The "average thickness" of the negative electrode substrate refers to the average value of the thickness measured at five arbitrary locations using a micrometer. The same applies to the average thickness of the separator, substrate layer, and inorganic material layer below.

[0078] (1st layer) The first layer contains a non-lithium metal. Preferably, the first layer contains a non-lithium metal as its main component. Here, "main component" refers to the component with the highest content, for example, a component with a content of 50% by mass or more. The lower limit of the non-lithium metal content in the first layer is preferably 50% by mass, more preferably 90% by mass, even more preferably 95% by mass, and even more preferably 99% by mass. By having a non-lithium metal content in the first layer that is above the lower limit, the growth of dendrites can be suppressed more reliably. On the other hand, the upper limit of the non-lithium metal content in the first layer may be 100% by mass.

[0079] The lower limit of the average thickness of the first layer described above is preferably 5 nm, and more preferably 10 nm. On the other hand, the upper limit of the average thickness of the first layer described above is preferably 200 nm, and more preferably 150 nm. When the average thickness of the first layer described above is within the above range, dendrite growth is more reliably suppressed. The average thickness of the first layer is determined by dividing the mass of the first layer by the area of ​​the first layer, and then by the true density of the first layer. If the average thickness of the first layer cannot be determined by this method due to the first layer being porous or an alloy, it may be determined by subtracting the average thickness of the negative electrode substrate and the average thickness of the lithium metal layer from the average thickness of the entire negative electrode. In this case, the average thickness of the negative electrode and the lithium metal layer refers to the average value measured at any five locations using a micrometer.

[0080] In terms of generating lithium metal crystals relatively uniformly across the entire separator-side surface of the first layer, it is preferable that the first layer be non-porous and dense. In this respect, it is preferable that the first layer be formed by sputtering, as it is both non-porous and dense.

[0081] The non-lithium metal is preferably a metal other than the main component metal of the negative electrode substrate. The non-lithium metal has a high affinity for lithium metal. Due to this high affinity, when lithium metal crystals precipitate between the first layer and the second layer, these lithium metal crystals tend to form relatively uniformly across the entire surface of the first layer, and particulate lithium metal crystals tend to form in a relatively dense state. This reduces dendrite growth, while at the same time making it easier to form the layer of particulate lithium metal crystals with a more uniform thickness and smoother surface. The affinity of the non-lithium metal for lithium metal can also be rephrased as the affinity of lithium metal for non-lithium metal, or the affinity between non-lithium metal and lithium metal.

[0082] In addition, it is preferable that the non-lithium metal also has high wettability to the lithium-ion conductive polymer solution of the second layer. When this wettability is high, a second layer can be formed on the first layer that has better adhesion to the first layer, is more uniform in thickness, and is smoother, thereby suppressing localized crystal formation of lithium metal caused by inferior properties. Furthermore, cracking of the second layer due to the crystal growth of lithium metal can be suppressed. Note that the wettability of the non-lithium metal to the lithium-ion conductive polymer solution can be rephrased as the wettability of the lithium-ion conductive polymer to the non-lithium metal, or the wettability between the non-lithium metal and the lithium-ion conductive polymer.

[0083] As described above, considering that the first and second layers cooperate to suppress dendrite growth while simultaneously generating a smooth layer of particulate lithium metal crystals, it is preferable that both the affinity of the non-lithium metal to the lithium metal and the wettability of the non-lithium metal to the lithium-ion conductive polymer solution are high.

[0084] As an indicator of the affinity of a non-lithium metal to a lithium metal and the wettability of a non-lithium metal to a lithium-ion conductive polymer solution, the contact angle of the reference solution to the non-lithium metal, using a polyvinyl carbonate (PVC) solution as the reference solution, can be cited. The smaller the contact angle of the reference solution to the non-lithium metal, the higher the affinity of the non-lithium metal to the lithium metal and the higher the wettability of the non-lithium metal to the lithium-ion conductive polymer solution tend to be. On the other hand, if the contact angle is too small, it may become difficult to form the second layer on the first layer. Taking this into consideration, the lower limit of the contact angle of the reference solution to the non-lithium metal is preferably, for example, 2°, and more preferably 5°. On the other hand, the upper limit of the contact angle is preferably, for example, 40°, and more preferably 35°.

[0085] The above contact angle is measured as follows. First, a PVC solution obtained by mixing PVC and dimethyl sulfoxide (DMSO) in a mass ratio of 15:85 is used as the reference solution. 0.02 mL of this reference solution is dropped onto the upper surface of a 20 mm diameter disc-shaped non-lithium metal at 25°C. Next, 10 minutes after dropping, a photograph of the droplets of the non-lithium metal and the reference solution is taken from any side (parallel to the upper surface of the non-lithium metal). In the obtained image, the angle between the tangent line to the contour curve of the droplet at any one intersection point of the contour curve and the upper surface of the non-lithium metal and the upper surface of the non-lithium metal is measured, and this angle is determined to be the contact angle. A smaller contact angle indicates a higher affinity of the non-lithium metal to the lithium metal and a higher wettability of the non-lithium metal to the lithium-ion conductive polymer solution.

[0086] In addition to the contact angle mentioned above, indicators of the affinity of the non-lithium metal to the lithium metal and the wettability of the non-lithium metal to the lithium-ion conductive polymer solution include the degree of spreading of the reference solution on the surface of the non-lithium metal. The greater the degree of spreading of the reference solution on the surface of the non-lithium metal, the higher the affinity of the non-lithium metal to the lithium metal and the higher the wettability of the non-lithium metal to the lithium-ion conductive polymer solution. Considering this point, the lower limit of the degree of spreading of the reference solution (maximum droplet diameter) on the surface of the non-lithium metal is preferably 6.0 mm, and more preferably 6.5 mm. On the other hand, the upper limit of the degree of spreading of the reference solution is not particularly limited. For example, the upper limit may be 10 mm.

[0087] The degree of spreading of the above solution is measured as follows. First, using the above-mentioned reference solution, 0.02 mL of this reference solution is dropped onto the upper surface of a 20 mm diameter disc-shaped non-lithium metal sample at 25°C. Next, 5 minutes after dropping, photographs of the droplets of the non-lithium metal and the reference solution are taken from above (perpendicular to the upper surface of the non-lithium metal). The maximum diameter of the contour curve of the droplet is measured in the obtained image, and the obtained maximum diameter is determined to be the degree of spreading. A larger degree of spreading indicates a higher affinity of the non-lithium metal to the lithium metal and a higher wettability of the non-lithium metal to the lithium-ion conductive polymer solution.

[0088] Furthermore, it is preferable that the wettability of the non-lithium metal to the lithium-ion conductive polymer solution is higher than that of the lithium metal to the lithium-ion conductive polymer solution. That is, it is preferable that the contact angle of the reference solution to the non-lithium metal is smaller than that of the reference solution to the lithium metal, and that the degree of spreading of the reference solution on the surface of the non-lithium metal is greater than the degree of spreading of the reference solution on the surface of the lithium metal. By having a higher wettability of the non-lithium metal to the lithium-ion conductive polymer solution than that of the lithium metal to the lithium-ion conductive polymer solution, the affinity between the first layer and the lithium metal can be increased, and the affinity between the first layer and the second layer can also be increased.

[0089] The non-lithium metals mentioned above are gold, platinum, or combinations thereof. Because the first layer contains gold, platinum, or combinations thereof as metals, the affinity between the first layer and lithium metal is high. As a result, the lithium metal crystals formed between the first and second layers are more likely to form more uniformly across the entire surface of the separator side of the first layer, and particulate lithium metal crystals are more likely to form in a relatively dense state, thus making it easier for the layer of particulate lithium metal crystals to grow into a smoother layer. In addition, the affinity between the first and second layers is also improved, so when forming the second layer on the first layer, the second layer is more likely to form more uniformly on the first layer, improving the adhesion of the second layer to the first layer, the uniformity of the thickness of the second layer, and the smoothness of the second layer. As a result, the localized formation of lithium metal crystals can be further suppressed. Therefore, the growth of dendrites is further suppressed.

[0090] As mentioned above, it is preferable that the first layer is non-porous and dense in order to enhance its affinity for lithium metal.

[0091] (2nd layer) The second layer described above contains a lithium-ion conductive polymer and a lithium salt, and is a layer capable of restricting the passage of the non-aqueous electrolyte. This second layer is not a solid electrolyte interface (SEI) formed by decomposition products of the non-aqueous electrolyte during charging of the energy storage element, but a layer formed during the manufacturing of the energy storage element. While the SEI is a non-uniform and porous layer due to its formation process, the second layer is preferably a more uniform and non-porous layer compared to the SEI. When the second layer is non-porous in this way, it can more effectively restrict the passage of the non-aqueous electrolyte, while allowing lithium ions to pass through due to the presence of the lithium-ion conductive polymer. In contrast, the SEI allows the non-aqueous electrolyte to pass through. A "non-porous layer" refers to a layer that does not have continuous pores in the thickness direction through which the non-aqueous electrolyte can pass, although this layer may have pores that do not allow the non-aqueous electrolyte to pass through.

[0092] As described above, the porous SEI allows the non-aqueous electrolyte to pass through to the first layer, causing localized formation of lithium metal crystals on the separator-side surface of the first layer and facilitating dendrite growth. In contrast, the second layer restricts the passage of the non-aqueous electrolyte, thereby suppressing localized lithium metal crystal formation on the separator-side surface of the first layer, while allowing relatively uniform formation of lithium metal crystals across the entire surface. Furthermore, if the second layer is non-porous as described above, it can suppress dendrite growth and prevent dendrites from penetrating the second layer. Moreover, because the second layer contains the lithium-ion conductive polymer, it is flexible and can expand and contract to conform to the crystal shape of the lithium metal deposited between the first and second layers. This suppresses the occurrence of cracks and other damage associated with the crystal growth of lithium metal in the second layer. In contrast, the SEI does not contain the lithium-ion conductive polymer and therefore lacks flexibility.

[0093] The lower limit of the lithium-ion conductive polymer content in the second layer is preferably 30% by mass, more preferably 50% by mass, even more preferably 70% by mass, and even more preferably 90% by mass. A lithium-ion conductive polymer content above this lower limit ensures more reliable suppression of dendrite growth. On the other hand, the upper limit of the lithium-ion conductive polymer content in the second layer is preferably 99% by mass, and more preferably 95% by mass.

[0094] The lower limit of the average thickness of the second layer is preferably 0.01 μm, more preferably 0.1 μm, and even more preferably 0.5 μm. On the other hand, the upper limit of the average thickness of the second layer is preferably 3 μm, and more preferably 1 μm. When the average thickness of the second layer is within the above range, dendrite growth is more reliably suppressed. The average thickness of the second layer is determined by subtracting the average thickness of the negative electrode substrate, the average thickness of the lithium metal layer, and the average thickness of the first layer from the average thickness of the entire negative electrode.

[0095] The lithium-ion conductive polymer described above is preferably one that does not easily swell (is poorly miscible) with non-aqueous electrolytes. In this respect, the lithium-ion conductive polymer is preferably a carbonate-based polymer, a nitrile-based polymer, or a combination thereof; that is, it is preferably formed from a polymer material containing a carbonate-based monomer, a nitrile-based monomer, or a combination thereof. Such a lithium-ion conductive polymer has structural units derived from the carbonate-based monomer or nitrile-based monomer.

[0096] Examples of carbonate monomers include linear carbonate monomers and cyclic carbonate monomers, of which cyclic carbonate monomers are preferred. Examples of the above cyclic carbonate monomers include vinylene carbonate (VC), ethylene carbonate (EC), propylene carbonate (PC), etc., and one of these may be used alone or in combination of two or more. Of these, VC or PC is preferred as the carbonate monomer for the lithium-ion conductive polymer, with VC being more preferred. That is, it is more preferable that the lithium-ion conductive polymer is formed from a polymer material containing VC as a monomer. Because the second layer is formed from a polymer material containing VC as a monomer, the second layer is less likely to swell the non-aqueous electrolyte, thus further reducing direct contact between the non-aqueous electrolyte and the first layer. Therefore, dendrite growth is further suppressed.

[0097] Nitrile monomers are monomers having a carbon-carbon double bond and a nitrile group. Examples of nitrile monomers include acrylonitrile (AN) and methacrylonitrile, and one of these may be used alone or in combination of two or more. Of these, AN is preferred as the nitrile monomer for the lithium-ion conductive polymer. That is, it is more preferable that the lithium-ion conductive polymer is formed from a polymer material containing AN as a monomer. Because the second layer is formed from a polymer material containing AN as a monomer, the second layer is less likely to swell the non-aqueous electrolyte, thus further reducing direct contact between the non-aqueous electrolyte and the first layer. Therefore, dendrite growth is further suppressed. In addition, the second layer (nitrile second layer) formed from a polymer material containing nitrile monomers tends to have a smaller swelling amount of the non-aqueous electrolyte per unit mass than the second layer (carbonate second layer) formed from carbonate monomers, thus further reducing direct contact between the non-aqueous electrolyte and the first layer. On the other hand, the nitrile second layer tends to have higher resistance than the carbonate second layer, so it is preferable for the nitrile second layer to contain a lithium salt in order to improve lithium ion conductivity.

[0098] Furthermore, the above polymer material may contain both carbonate monomers and nitrile monomers. The above lithium-ion conductive polymer may be a copolymer formed of carbonate monomers and nitrile monomers, or a mixture of polymers formed of only one of these. In addition, the above polymer material may contain monomers other than carbonate monomers and nitrile monomers. Furthermore, the above lithium-ion conductive polymer may be a polymer formed of at least one of carbonate monomers and nitrile monomers, a copolymer formed of at least one of carbonate monomers and nitrile monomers and other monomers, or a mixture of polymers formed of only one of these. For example, the lithium-ion conductive polymer may be a copolymer of at least one of polyvinylene carbonate (PVC) and polyacrylonitrile (PAN), at least one of VC and AN and other monomers, or a mixture thereof. The content of at least one of the carbonate monomer and the nitrile monomer relative to the total amount of other monomers (total monomers) is preferably 10 mol% to 90 mol%, and preferably 20 mol% to 80 mol%.

[0099] The second layer further contains a lithium salt. The inclusion of a lithium salt in the second layer increases its flexibility, thereby further suppressing cracking and other damage to the second layer. This further inhibits dendrite growth. In addition, the inclusion of a lithium salt in the second layer improves its lithium ion conductivity, further suppressing localized current concentration. This also further inhibits dendrite growth.

[0100] The lower limit of the lithium salt content in the second layer is preferably 2% by mass, and more preferably 5% by mass. Furthermore, the lower limit of the lithium salt content per 100 parts by mass of lithium conductive polymer in the second layer is preferably 2 parts by mass, and more preferably 5 parts by mass. On the other hand, the upper limit of the lithium salt content in the second layer is preferably 70% by mass, more preferably 50% by mass, even more preferably 30% by mass, and even more preferably 20% by mass. Furthermore, the upper limit of the lithium salt content per 100 parts by mass of lithium conductive polymer in the second layer is preferably 240 parts by mass, more preferably 100 parts by mass, and even more preferably 50 parts by mass. A lithium salt content above the lower limit allows for more reliable suppression of dendrite growth. On the other hand, a lithium salt content below the upper limit reduces the amount of swelling of the non-aqueous electrolyte in the second layer.

[0101] The lithium salt is preferably compatible with the lithium-ion conductive polymer. Furthermore, it is preferable that the lithium salt is relatively poorly soluble in non-aqueous electrolytes. Considering this, the lithium salt can be appropriately selected depending on the type of non-aqueous electrolyte and lithium-ion conductive polymer. For example, examples of the lithium salt include lithium difluorophosphate (LiDFP), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and among these, LiDFP, LiDFOB, LiTFSI, or a combination thereof are preferred. The second layer may contain the lithium salt alone or two or more types. When the lithium salt is the compound described above, the flexibility of the second layer can be further increased, thus further suppressing cracking of the second layer. This further suppresses dendrite growth.

[0102] (Lithium metal layer) The negative electrode preferably further comprises a lithium metal layer (hereinafter also referred to as the "first lithium metal layer") between the first layer and the separator, and more preferably comprises the first lithium metal layer between the first layer and the second layer. The first lithium metal layer functions as a negative electrode active material layer or a lithium metal replenishment layer. Therefore, the first lithium metal layer contributes to charging and discharging as a negative electrode active material layer and can also replenish the amount of electricity corresponding to the lithium metal that has become unable to contribute to charging and discharging due to the electrical isolation of grown dendrites, although this amount has been reduced. As shown in Figure 2, when the negative electrode comprises the first lithium metal layer between the first layer and the second layer, the first lithium metal layer can be formed as a layer of particulate lithium metal crystals between the first layer and the second layer by charging (initial charging and subsequent charging), as described above. When the negative electrode comprises the first lithium metal layer formed by charging, the first lithium metal layer does not need to be present in the discharge state.

[0103] When the first lithium metal layer is formed by charging, its average thickness depends on the capacity density and charge / discharge depth during the charging and discharging of the energy storage element. Therefore, the average thickness of the first lithium metal layer is set appropriately according to the capacity density and charge / discharge depth.

[0104] The negative electrode further comprises a lithium metal layer (hereinafter also referred to as the "second lithium metal layer") between the negative electrode substrate and the first layer. The second lithium metal layer functions as a negative electrode active material layer or a lithium metal replenishment layer. Therefore, the second lithium metal layer contributes to charging and discharging as a negative electrode active material layer and can also replenish the amount of electricity corresponding to the lithium metal that can no longer contribute to charging and discharging due to the electrical isolation of the dendrites. The second lithium metal layer is formed between the negative electrode substrate and the first layer during the manufacture of the energy storage element. The second lithium metal layer can be manufactured, for example, by cutting or shaping a lithium metal foil into a predetermined shape.

[0105] As mentioned above, considering that the second lithium metal layer is a lithium metal replenishment layer, a larger average thickness of the second lithium metal layer is preferable because it allows for longer charge-discharge cycles. For example, the average thickness of the second lithium metal layer may be set so that the energy storage element achieves a mass energy density of 400 Wh / kg and maintains an 80% capacity retention rate after 200 charge-discharge cycles. On the other hand, a larger average thickness of the second lithium metal layer may lead to the energy storage element becoming unnecessarily large. The average thickness of the second lithium metal layer is also set according to the Coulomb efficiency during charge-discharge. Therefore, the average thickness of the second lithium metal layer should be set appropriately, taking these points into consideration. For example, the lower limit of the average thickness of the second lithium metal layer is preferably greater than 0 μm, and even more preferably 10 μm. On the other hand, the upper limit of the average thickness of the second lithium metal layer may be preferably 100 μm, and even more preferably 60 μm. Note that "average thickness of the second lithium metal layer" refers to the average value of the thickness measured at any five points. This average thickness is calculated by subtracting the average thickness of the negative electrode substrate from the average thickness measured at any five points on the laminate of the negative electrode substrate and the second lithium metal layer.

[0106] The first and second lithium metal layers described above contain lithium metal as a negative electrode active material. The inclusion of lithium metal as a negative electrode active material in the first and second lithium metal layers improves the discharge capacity per unit mass of active material. The lithium metal includes not only pure lithium metal but also lithium alloys. Examples of lithium alloys include lithium aluminum alloy.

[0107] When a metal foil (e.g., copper foil) is used as the negative electrode substrate, an alloy layer containing a metal (e.g., copper metal) and lithium metal, which are components of the negative electrode substrate, may be formed between the negative electrode substrate and the second lithium metal layer.

[0108] The above-mentioned negative electrode may include an intermediate layer between the negative electrode substrate and the second lithium layer. This intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode substrate and the second lithium metal layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0109] (Separator) The separator has a base layer. The separator may also have a base layer and an inorganic material layer disposed on the negative electrode side of the base layer. When the separator has the inorganic material layer in this way, the presence of this inorganic material layer prevents the lithium metal deposited as described above from growing toward the separator. Therefore, penetration of the separator by the lithium metal is suppressed, and the occurrence of short circuits is further suppressed.

[0110] Thus, as a separator, for example, a separator consisting only of a base layer, or a separator in which an inorganic material layer is formed on one or both sides of the base layer can be used. Examples of the shape of the base layer include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

[0111] The inorganic material layer described above is a layer formed using inorganic particles as the forming material. This inorganic material layer is a porous layer. The inorganic material layer preferably has heat resistance. The inorganic particles preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Examples of inorganic compounds constituting the above inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials or artificial products thereof such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. These inorganic compounds may be used individually or in combination, or two or more may be mixed. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for the energy storage element. The above inorganic material layer may contain a binder, and the same type of binder as that contained in the positive electrode active material layer described above can be used.

[0112] The porosity of the separator is preferably 80 volume% or less from the viewpoint of strength, and preferably 20 volume% or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

[0113] When the separator has the above-mentioned base material layer and the above-mentioned inorganic material layer, the separator is manufactured by, for example, mixing the above-mentioned inorganic particles, a binder and a known dispersion medium such as an organic solvent, applying the resulting mixture to at least one surface of the base material layer, and drying the dispersion medium. Alternatively, the separator may be manufactured by, for example, applying the above-mentioned mixture onto a known base material, drying it to form a sheet-like inorganic material layer, peeling the resulting inorganic material layer from the base material, and laminating it onto at least one surface of the base material layer using a known adhesive.

[0114] The larger the average thickness of the substrate layer, the more difficult it tends to be for dendrites to penetrate the substrate layer. On the other hand, if the average thickness of the substrate layer is too large, the mass energy density of the energy storage element tends to decrease. Therefore, the average thickness of the substrate layer can be appropriately set considering these points, for example, with a preferred lower limit of 3 μm and a more preferred lower limit of 6 μm. On the other hand, with a preferred upper limit of 50 μm and a more preferred lower limit of 25 μm.

[0115] The larger the average thickness of the inorganic material layer, the more difficult it tends to be for dendrites to penetrate the inorganic material layer. Also, because the inorganic material layer is a porous layer, the larger the average thickness of the inorganic material layer, the more uniform the current distribution tends to be. On the other hand, if the average thickness of the inorganic material layer is too large, the mass energy density of the energy storage element tends to decrease. Therefore, the average thickness of the inorganic material layer can be appropriately set considering these points. For example, a lower limit for the average thickness of the inorganic material layer is preferably 2 μm, and 3 μm may be more preferable. On the other hand, a higher limit for the average thickness of the inorganic material layer is preferably 10 μm, and 6 μm may be more preferable.

[0116] (Layer structure of the electrode body) As shown in Figures 1 and 2, the following are some examples of the layer configuration of the electrode body provided in the energy storage element.

[0117] For example, in the embodiment shown in Figure 1, the electrode body 2 has a positive electrode 6, a separator 9, and a negative electrode 12. Specifically, in the embodiment shown in Figure 1, the positive electrode 6 has a positive electrode substrate 7 and a positive electrode active material layer 8 disposed on the separator 9 side of the positive electrode substrate 7. The separator 9 has a substrate layer 10 and an inorganic material layer 11 disposed on the negative electrode 12 side of the substrate layer 10. The negative electrode 12 has a negative electrode substrate 13, a first layer 14 disposed on the separator 9 side of the negative electrode substrate 13, and a second layer 15 disposed on the separator 9 side of the first layer 14, and has a layer structure with a second lithium metal layer 17 further between the negative electrode substrate 13 and the first layer 14. In the electrode body 2 having the layer structure shown in Figure 1, charging may cause lithium metal crystals to precipitate between the first layer 14 and the second layer 15, thereby forming the first lithium metal layer 16 as shown in Figure 2, and the layer structure of the electrode body 2 may change to the layer structure shown in Figure 2. On the other hand, discharging may cause the layer structure of the electrode body 2 to return to the layer structure of Figure 1.

[0118] For example, in the embodiment shown in Figure 2, the electrode body 2 has the same layer configuration as in Figure 1, except that the negative electrode 12 has an additional first lithium metal layer 16 between the first layer 14 and the second layer 15. The first lithium metal layer 16 of the electrode body 2 shown in Figure 2 may be formed when the electrode body 2 shown in Figure 1 is charged, and the layer configuration of the electrode body 2 may change to the layer configuration of Figure 1 due to discharge.

[0119] (Non-aqueous electrolytes) As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0120] As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogens may also be used.

[0121] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, EC and FEC are preferred.

[0122] Examples of linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate (TFEMC), and bis(trifluoroethyl) carbonate. Among these, DMC, EMC, and TFEMC are preferred.

[0123] It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0124] Lithium salts are typically used as the electrolyte salt.

[0125] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalate salts such as lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), and lithium bis(oxalato)difluorophosphate (LiFOP); and lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0126] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3 Preferably, it is 0.3 mol / dm³ 3 More than 2.0mol / dm 3 It is more preferable that it be less than or equal to 0.5 mol / dm 3 More than 1.7mol / dm 3 It is even more preferable that the following is the case: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0127] Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), and lithium bis(oxalato)difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyls, alkylbiphenyls, terphenyls, partially hydrogenated terphenyls, and cyclohexyl biphenyls. Aromatic compounds such as silbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, and ethylvinylene carbonate Succinic acid anhydride, glutaric acid anhydride, maleic acid anhydride, citraconic acid anhydride, glutaconic acid anhydride, itaconic acid anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3) Examples include 2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithtrimethylsilyl titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used individually or in combination of two or more.

[0128] The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further improve safety.

[0129] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0130] The solid electrolyte can be selected from any material that has lithium ion conductivity and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0131] Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 These are some examples.

[0132] The shape of the energy storage element in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like. Figure 3 shows an example of a rectangular battery, specifically an energy storage element 1. Note that this figure is a transparent view of the inside of the container. An electrode body 2, having a positive electrode and a negative electrode wound around a separator, is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51. A non-aqueous electrolyte is injected into the container 3.

[0133] In this embodiment, it is preferable that the electrode body of the energy storage element is pressed in the thickness direction. When the electrode body is pressed in the thickness direction in this manner, it tends to be more prone to short circuits compared to when it is not pressed, but even in this case, the occurrence of short circuits is suppressed. Therefore, when the electrode body is pressed in the thickness direction, the effect of suppressing the growth of dendrites in the energy storage element is particularly fully exhibited. For example, in the energy storage element 1 shown in Figure 3, the electrode body 2 can be pressed in the thickness direction by constraining the container 3 with a restraining member (not shown) or the like in the thickness direction of the electrode body 2 (from the front left to the back right in Figure 3). The pressure applied to the container is adjusted, for example, by changing the distance in the thickness direction of the restraining member. The lower limit of the pressing force is preferably 0.01 MPa, and more preferably 0.2 MPa. On the other hand, the upper limit of the pressing force is preferably 2 MPa, and more preferably 1 MPa. When the pressing force is within the above range, the effect of suppressing the growth of dendrites is more fully exhibited. The above pressing force is measured by observing the change in color of pressure-sensitive paper placed between the restraining member and the energy storage element 1 being pressed.

[0134] <Configuration of the energy storage device> The energy storage elements of this embodiment can be mounted as an energy storage unit (battery module) comprising multiple energy storage elements in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power supplies for power storage. In this case, it is sufficient that the technology of the present invention is applied to at least one of the energy storage elements included in the energy storage unit. Figure 4 shows an example of a power storage device 30 which is formed by further assembling power storage units 20, each of which is an assembly of two or more electrically connected power storage elements 1. The power storage device 30 may include busbars (not shown) that electrically connect two or more power storage elements 1, busbars (not shown) that electrically connect two or more power storage units 20, etc. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more power storage elements.

[0135] The energy storage device of this embodiment comprises one or more energy storage elements and a restraining member that restrains the one or more energy storage elements, and it is preferable that the electrode body is pressed down by the one or more energy storage elements being pressed in the thickness direction by the restraining member. In such an energy storage device, for example, in an energy storage device 30 comprising multiple energy storage elements 1 as shown in Figure 4, the electrode body 2 of the multiple energy storage elements 1 can be pressed in the thickness direction by restraining the multiple energy storage elements 1 in the thickness direction (left-right direction in Figure 4) by a restraining member (not shown). Furthermore, if the energy storage device comprises one energy storage element, the electrode body can be pressed in the thickness direction by restraining this energy storage element in the thickness direction of the electrode body by a restraining member.

[0136] <Manufacturing method for energy storage elements> The manufacturing method for the energy storage element of this embodiment comprises preparing a positive electrode, preparing a separator, preparing a negative electrode, stacking the positive electrode, the separator, and the negative electrode in this order to create an electrode body, and housing the electrode body and a non-aqueous electrolyte in a container. The preparation of the negative electrode comprises forming a first layer containing gold, platinum, or a combination thereof directly or indirectly on the separator side of the negative electrode substrate, forming a second layer on the separator side of the first layer containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte, and forming a lithium metal layer between the negative electrode substrate and the first layer. The manufacturing method for the energy storage element may further comprise pressing the container in the thickness direction of the electrode body. According to the manufacturing method for the energy storage element, the above-described energy storage element can be manufactured. That is, an energy storage element in which dendrite growth is suppressed can be manufactured.

[0137] (Preparing the positive electrode) The positive electrode described above will be prepared, and the positive electrode described above will be used.

[0138] (Preparing the separator) The above-mentioned separator will be prepared and used.

[0139] (Preparing the negative electrode) To prepare the above-mentioned negative electrode, a first layer containing gold, platinum, or a combination thereof (non-lithium metal) is formed directly or indirectly on the separator side of the negative electrode substrate; a second layer containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte is formed on the separator side of the first layer; and a lithium metal layer is formed between the negative electrode substrate and the first layer.

[0140] To form the first layer on the separator side of the negative electrode substrate, sputtering, vapor deposition, plating, coating, etc., of the first layer forming material mainly composed of a non-lithium metal can be applied directly or indirectly to the surface of the negative electrode substrate. Of these methods, sputtering the first layer forming material is preferred in that it forms a denser layer.

[0141] The second layer can be formed on the separator side of the first layer, and a material for forming the second layer, mainly composed of the lithium conductive polymer and containing a lithium salt, can be applied to the first layer formed on the negative electrode substrate. The material for forming the second layer can be prepared, for example, by dissolving the lithium conductive polymer and lithium salt in a solvent. Examples of the solvent include DMSO.

[0142] The lithium-ion conductive polymer described above can be obtained as follows. Specifically, a solution is obtained by mixing a carbonate monomer such as VC, a nitrile monomer such as AN, or a combination thereof, and optionally a monomer other than a carbonate monomer or a nitrile monomer, with a solvent such as N,N-dimethylformamide (DMF) at room temperature, or while heating as needed for speed, etc. A polymerization initiator such as a radical reaction initiator such as azobisisobutyronitrile (AIBN) is added to the solution, and the monomers are polymerized to obtain the product by standing overnight in a constant temperature bath at a predetermined temperature according to the type of monomer and polymerization initiator. The obtained product can be purified by washing and recrystallizing the product using known methods to obtain a purified lithium-ion conductive polymer.

[0143] In applying the forming material for the second layer to the separator side of the first layer, for example, first, droplets of the forming material for the second layer are applied to the separator side surface of the first layer so that the amount of droplets per unit area is the same. Then, by natural drying and reduced-pressure drying, the second layer is laminated and formed on the separator side surface of the first layer. Examples of methods for applying the forming material for the second layer include spraying, dip coating, spin coating, and roll coating.

[0144] If the negative electrode further includes the first lithium metal layer disposed between the first layer and the separator, more preferably between the first layer and the second layer, the first lithium metal layer can be formed between the first layer and the second layer by the deposition of lithium metal accompanying the charging of the energy storage element.

[0145] To form the lithium metal layer between the negative electrode substrate and the first layer, for example, a lithium metal foil can be cut into a predetermined shape or molded into a predetermined shape as the second lithium metal layer, and after pressing the negative electrode substrate and the lithium metal foil together, the first layer can be formed on the separator side of the lithium metal foil.

[0146] (Fabrication of electrode bodies) To manufacture the electrode body, for example, the positive electrode, the separator, and the negative electrode can be stacked or wound together in this order. If the separator has the base material layer and the inorganic material layer, in manufacturing the electrode body, the positive electrode, the separator, and the negative electrode can be stacked or wound together in this order, and the inorganic material layer of the separator can face the negative electrode.

[0147] (Placement in a container) The above-mentioned electrode body and non-aqueous electrolyte can be housed in a container using any known method. For example, when a non-aqueous electrolyte is used, the electrode body is housed in a container, the non-aqueous electrolyte is injected through an inlet formed in the container, and then the inlet is sealed. Details of the other elements constituting the energy storage element obtained by this manufacturing method are as described above.

[0148] (Pressure on the electrode) One way to achieve this is to press the electrode body in the thickness direction, by restraining the container with a restraining member (not shown) or the like so that the electrode body is pressed in the thickness direction.

[0149] As described above, the energy storage element of this embodiment has suppressed dendrite growth. The method for manufacturing the energy storage element of this embodiment can manufacture an energy storage element in which dendrite growth is suppressed. The energy storage device of this embodiment has suppressed dendrite growth.

[0150] <Other Embodiments> Furthermore, the energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0151] In the above embodiment, the case in which the energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors.

[0152] In Figures 1 and 2 of the above embodiment, the separator is shown to have a base material layer and an inorganic material layer, but for example, the separator may have only a base material layer. [Examples]

[0153] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0154] [Test Examples 1 to 6] (Manufacturing of the laminate in Test Example 1) As a negative electrode substrate on which a second lithium metal layer is laminated, a disc-shaped copper-lithium metal laminate with a diameter of 20 mm (manufactured by Honjo Metal Co., Ltd.) was prepared, consisting of a lithium metal plate with an average thickness of 60 μm laminated on a copper foil with an average thickness of 10 μm.

[0155] A JEOL MAGNETRON SPUTTERING DEVICE (JUC-5000) was used as the sputtering apparatus, and 99.99% pure gold (Au) was used as the target. The height from the surface of the lithium metal plate to the target in the copper-lithium metal laminate was set to 25 mm, and the current was set to 10 mA. Gold was sputtered onto the surface of the laminate where the lithium metal plate was stacked. The sputtering was performed for 5 minutes each, for a total of three times. All of the above work was performed in a dry room. The average thickness of the first layer containing gold as the metal formed by the above sputtering was 50 nm. In this way, the laminate of Test Example 1 was obtained.

[0156] (Manufacturing of laminates for test examples 2 and 3) Laminates for Test Examples 2 and 3 were obtained in the same manner as in Test Example 1, except that the metals shown in Table 1 were used as targets, and in which copper foil, lithium metal plate, and a first layer formed of the metals shown in Table 1 were laminated in that order.

[0157] (Manufacturing of metal foils in Test Examples 4 to 6) For Test Examples 4 through 6, the metal foils shown in Table 1 were cut into 20mm diameter disc shapes and used. In Test Example 4, the copper-lithium metal laminate prepared in Test Example 1 was used.

[0158] (Evaluation of affinity and wettability of the first layer in the laminates of Test Examples 1 to 3 and the metal foils of Test Examples 4 to 6) Using the laminates and metal foils obtained from Test Examples 1 to 6 as described above, the affinity and wettability of the metals contained in the first layer of the laminates in Test Examples 1 to 3 and the metal foils (corresponding to the first layer) in Test Examples 4 to 6 were evaluated by measuring the contact angle of the reference solution and the degree of spreading of the reference solution (maximum droplet diameter) using the measurement method described above. The results are shown in Table 1.

[0159] [Example 1] (Fabrication of the negative electrode) Similar to Test Example 1, a copper-lithium metal laminate was prepared as a negative electrode substrate on which a second lithium metal layer was laminated. This laminate consisted of a copper foil with an average thickness of 10 μm, on which a lithium metal plate with an average thickness of 60 μm was laminated as the second lithium metal layer. In the same manner as in Test Example 1, a first layer was laminated onto the surface of this copper-lithium metal laminate on the side where the lithium metal plate was laminated by sputtering gold (Au). The average thickness of the resulting first layer was 50 nm.

[0160] A second layer was formed on the surface of the obtained first layer by the following procedure. A solution was obtained by mixing 10 g of VC and 2 mL of N,N-dimethylformamide (DMF), to which 0.06 g of azobisisobutyronitrile (AIBN), a radical reaction initiator, was added, and the mixture was left to stand overnight in a 60°C bath to synthesize a product containing PVC. 20 mL of DMF was added to the obtained product, and the product was redissolved in DMF by stirring while heating at 60°C. Although the product could be dissolved in DMF at room temperature, heating was performed as described above for the sake of speed. The obtained solution was recrystallized by gradually adding it dropwise to 1 L of ethanol being stirred at 350 rpm. After removing the supernatant ethanol from the product, impurities were removed by washing the product several times with ethanol. The final obtained product was filtered through a Buchner funnel and left to stand overnight in a 60°C bath to obtain purified PVC as a lithium-ion conductive polymer.

[0161] Next, a lithium ion conductive polymer solution was prepared as the material for forming the second layer by dissolving the PVC obtained above and LiDFP as a lithium salt in DMSO. The PVC content in this forming material was 20% by mass, and the LiDFP content was 0.6% by mass. That is, the LiDFP content was set to 3 parts by mass per 100 parts by mass of PVC. In other words, the PVC content (mixing amount 1) and the LiDFP content (mixing amount 2) were set to 97% by mass and 3% by mass relative to the total content of PVC and LiDFP. The obtained forming material was coated onto the first layer obtained above using the dip-coating method so that the amount of material dropped per unit area was the same, and then air-dried and dried under reduced pressure. The average thickness of the obtained second layer was 1.0 μm.

[0162] The negative electrode obtained in this way was in the form of a strip 32 mm wide and 42 mm long.

[0163] (Fabrication of the positive electrode) As the positive electrode active material, it has an α-NaFeO2 type crystal structure, Li 1+α Me 1-α A lithium transition metal composite oxide represented as O2 (where Me is a transition metal) was used. Here, the molar ratio of Li to Me (Li / Me) was 1.33, and Me consisted of Ni and Mn, with Ni:Mn present in a molar ratio of 0.33:0.67.

[0164] Next, a positive electrode paste was prepared using N-methylpyrrolidone (NMP) as the dispersion medium, containing the above-mentioned positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) and phosphonic acid as binders in a mass ratio of 92.25:4.5:3.0:0.25. The positive electrode paste was coated onto one side of an aluminum foil with an average thickness of 15 μm, which served as the positive electrode substrate. The foil was then dried and pressed to produce a positive electrode with a positive electrode active material layer. The coating amount of the positive electrode active material layer was 26.5 mg / cm². 2 The porosity was 40%. The fabricated positive electrode was in the shape of a strip, 30 mm wide and 40 mm long.

[0165] (Preparation of non-aqueous electrolytes) FEC and DMC were used as non-aqueous solvents. Then, LiPF6 was added at a volume ratio of 30:70 to a mixed solvent containing FEC and DMC. 3 The solution was dissolved at the specified concentration, and 1,3-propeneproton (PRS) was further mixed into this solution as an additive at a concentration of 2% by mass to obtain a non-aqueous electrolyte.

[0166] (Fabrication of energy storage elements) As a separator, a separator was used in which an inorganic material layer containing aluminosilicate particles, an inorganic material, was laminated on one side of a polypropylene microporous membrane, which served as the base layer. The average thickness of the separator was 21 μm, the average thickness of the base layer was 15 μm, and the average thickness of the inorganic material layer was 6 μm. The separator was positioned so that the inorganic material layer faced the negative electrode, and the electrode body was fabricated by laminating the positive electrode and the negative electrode through this separator. This electrode body was placed in a container, the non-aqueous electrolyte was injected into it, and then the container was sealed by heat welding to obtain the single-layer pouch cell of Example 1.

[0167] [Example 2] An energy storage element for Example 2 was obtained in the same manner as in Example 1, except that the average thickness of the second layer described above was set to 3.0 μm.

[0168] [Comparative Example 1] A comparative example of energy storage element 1 was obtained in the same manner as in Example 1, except that the negative electrode was fabricated without forming a second layer on the first layer.

[0169] [Comparative Example 2] A comparative energy storage element of Comparative Example 2 was obtained in the same manner as in Example 1, except that a first layer was formed by sputtering tin (Sn) instead of gold, and a negative electrode was fabricated without forming a second layer on the formed first layer. The average thickness of the first layer was 50 nm.

[0170] [Comparative Example 3] Comparative Example 3 was obtained in the same manner as in Example 1, except that a copper-lithium metal laminate similar to that in Example 1, with a second lithium metal layer laminated on it, was used as the negative electrode without forming either the first or second layer on the lithium metal plate.

[0171] (Initial charge / discharge 1) Each obtained energy storage element underwent two initial charge-discharge cycles at 25°C under the following conditions: Charging was performed using constant current-constant voltage (CCCV) charging with a charging current of 0.1C and a charging voltage of 4.6V, with the charging termination condition being when the charging current reached 0.05C. Discharging was performed using constant current (CC) discharge with a discharge current of 0.1C and a discharge termination voltage of 2.0V. A 10-minute rest period was provided after both charging and discharging. Note that 1C here represents the current per unit area of ​​the positive electrode, which is 6.0mA / cm². 2 That's what I decided.

[0172] (Charge-discharge cycle test 1) Each energy storage element after the initial charge / discharge cycle 1 was subjected to a 10-cycle charge / discharge test at 25°C under the following conditions: Charging was performed using constant current constant voltage (CCCV) charging with a charging current of 0.2C and a charging voltage of 4.6V, and the charging termination condition was when the charging current reached 0.05C. Discharging was performed using constant current (CC) discharge with a discharge current of 0.1C and a discharge termination voltage of 2.0V. A 10-minute rest period was provided after both charging and discharging. Note that 1C is the same as in the initial charge / discharge cycle 1 described above.

[0173] (Measurement of the average thickness of lithium metal dendrites deposited after charge-discharge cycle test 1) The average thickness of the lithium metal dendrites deposited after charge-discharge cycle test 1 in Examples 1, 2, and Comparative Examples 1 to 3 was measured as follows. Specifically, the energy storage element was disassembled after the 10th discharge cycle in charge-discharge cycle test 1, and the overall thickness of the negative electrode was measured at five arbitrary locations using a micrometer, and the average value was calculated. From the obtained overall average thickness of the negative electrode, the sum of the average thicknesses of the negative electrode substrate (10 μm), the second lithium metal layer (60 μm), the first layer (50 nm), and the second layer (1.0 μm and 3.0 μm) was subtracted to obtain the average thickness of the dendrites. Note that in charge-discharge cycles of about 10 times, the thickness of each layer of the negative electrode hardly changes, and in the discharged state, the first lithium metal layer is almost nonexistent, so the above average thickness is the average length of the dendrites in the stacking direction of the positive electrode, separator, and negative electrode. Furthermore, the above average thickness is an indicator of the likelihood of short circuits occurring and the amount of dendrites becoming electrically isolated. A larger average length indicates a higher likelihood of short circuits and greater dendrite isolation, while a smaller average length indicates a lower likelihood of short circuits and less dendrite isolation.

[0174] [Table 1]

[0175] [Table 2]

[0176] As shown in Table 1, gold and platinum, compared to the other metals in Table 1, have a smaller contact angle in the standard solution and a greater degree of spreading of the reference solution. This indicates high affinity for lithium metal and high wettability in the lithium-ion conductive polymer solution. Therefore, the first layer containing these non-lithium metals showed relatively high affinity for lithium metal and also relatively high affinity for the second layer. As shown in Table 2, Examples 1 and 2, which included the first and second layers, showed suppressed dendrite growth compared to Comparative Examples 1 to 3, which did not include at least one of the first and second layers. Furthermore, it was shown that the higher the wettability of the non-lithium metal in the first layer compared to lithium metal in the lithium-ion conductive polymer solution, the more effectively dendrite growth was suppressed.

[0177] For reference, the effect of the first layer on the crystal shape of the deposited lithium metal was investigated. Figure 5 shows an image obtained by observing the crystal shape of the lithium metal deposited on the first layer of the negative electrode after the first charge of initial charge-discharge 1 in Comparative Example 1 using a field emission scanning electron microscope (FE-SEM) from a direction perpendicular to the first layer. Similarly, Figure 6 shows an image obtained by observing the crystal shape of the lithium metal deposited on the second lithium metal layer of the negative electrode after the first charge of initial charge-discharge 1 in Comparative Example 3 using an FE-SEM from a direction perpendicular to the second lithium metal layer. As shown in Figure 5, when the negative electrode had the first layer, particulate lithium metal crystals formed a dense and smooth layer, whereas as shown in Figure 6, in Comparative Example 3, which did not have the first layer, a large amount of dendrites were deposited.

[0178] Thus, the shape of the lithium metal crystals deposited during the initial charge contributes to the suppression of dendrite growth. The reason for this is not entirely clear, but it can be inferred as follows: If relatively smooth lithium metal crystals are formed during the initial charge due to the presence of the first layer, the contact area between these smooth lithium metal (see Figure 5) and the non-aqueous electrolyte will be smaller than the contact area between non-smooth lithium metal (see Figure 6) and the non-aqueous electrolyte. Therefore, it is inferred that dendrite growth (average thickness) is reduced in subsequent charge-discharge cycles.

[0179] [Reference example 1] A power storage element of Reference Example 1 was fabricated in the same manner as in Example 1, except that tin (Sn) was sputtered onto the surface of the second lithium metal layer in the same manner as in Test Example 2 during the formation of the first layer, the average thickness of the second layer was set as shown in Table 3 during the formation of the second layer, and TFEMC was used instead of DMC in the preparation of the non-aqueous electrolyte.

[0180] [Reference example 2] In the formation of the second layer, polypropylene carbonate (PPC) was synthesized using PC instead of VC. Using the synthesized PPC, the energy storage element of Reference Example 2 was fabricated in the same manner as Reference Example 1, except that the average thickness of the second layer was set as shown in Table 4.

[0181] (Initial charge / discharge 2) For the energy storage elements of Reference Examples 1 and 2 and Comparative Examples 2 and 3 described above, the coating amount of the positive electrode active material layer was set to 32.0 mg / cm². 2 Assuming 1C, the current per unit area of ​​the positive electrode is 7.2mA / cm². 2 The initial charge and discharge was performed in the same manner as in initial charge and discharge 1, except for the following:

[0182] (Charge-discharge cycle test 2) For each energy storage element after initial charge and discharge 2, 1C is applied, and the current per unit area of ​​the positive electrode is 7.2 mA / cm². 2 The charge-discharge cycle test was performed in the same manner as in charge-discharge cycle test 1, except for the following:

[0183] (Measurement of the average thickness of lithium metal dendrites deposited after charge-discharge cycle test 2) The average thickness of lithium metal dendrites deposited after charge-discharge cycle test 2 in Reference Examples 1 and 2 and Comparative Examples 2 and 3 was measured in the same manner as described above for measuring the average thickness of dendrites. The results are shown in Table 3.

[0184] [Table 3]

[0185] As shown in Table 3, Reference Examples 1 and 2, which include the first and second layers, were shown to suppress dendrite growth compared to Comparative Examples 2 and 3, which do not include at least one of the first and second layers.

[0186] [Example 3] In forming the second layer, polyacrylonitrile (PAN, average molecular weight: 150,000, manufactured by Aldrich) was used instead of PVC, and LiTFSI was used as the lithium salt. PAN and LiTFSI were dissolved in DMSO. Specifically, 10 mL of DMSO was mixed with 1 g of PAN to dissolve the PAN in DMSO. The second layer forming material was prepared by dissolving LiTFSI in the resulting solution. The PAN content in this forming material was 10% by mass, and the LiTFSI content was 1% by mass. That is, the LiTFSI content was set to 10 parts by mass per 100 parts by mass of PAN. In other words, the PAN content (mixing amount 1) and the LiTFSI content (mixing amount 2) were set to 91% by mass and 9% by mass respectively, relative to the total content of PAN and LiTFSI. Using the forming material thus obtained, the energy storage element of Example 3 was fabricated in the same manner as in Example 1, except that the average thickness of the second layer was set as shown in Table 4.

[0187] [Example 4] An energy storage element for Example 4 was fabricated in the same manner as in Example 3, except that the PAN content in the forming material was 10% by mass and the LiTFSI content was 2.5% by mass (i.e., the LiTFSI content was set to 25 parts by mass per 100 parts by mass of PAN). Specifically, in Example 4, the PAN content (mixing amount 1) relative to the total content of PAN and LiTFSI was set to 80% by mass and the LiTFSI content (mixing amount 2) was set to 20% by mass.

[0188] [Example 5] The energy storage element of Example 5 was fabricated in the same manner as in Example 3, except that the PAN content in the forming material was 10% by mass and the LiTFSI content was 5% by mass (i.e., the LiTFSI content was set to 50 parts by mass per 100 parts by mass of PAN), and the average thickness of the second layer was as shown in Table 4. In other words, in Example 5, the PAN content (mixing amount 1) relative to the total content of PAN and LiTFSI was set to 67% by mass and the LiTFSI content (mixing amount 2) was set to 33% by mass. Note that the mixing amount 1 and mixing amount 2 in Example 5 are expressed rounded to the first decimal place.

[0189] [Example 6] The energy storage element of Example 6 was fabricated in the same manner as in Example 3, except that the content of PAN in the forming material was 10% by mass and the content of LiTFSI was 10% by mass (i.e., the content of LiTFSI was set to 100 parts by mass relative to 100 parts by mass of PAN), and the average thickness of the second layer was as shown in Table 4. In other words, in Example 6, the content of PAN (mixing amount 1) relative to the total content of PAN and LiTFSI was set to 50% by mass and the content of LiTFSI (mixing amount 2) was set to 50% by mass.

[0190] [Example 7] The energy storage element of Example 7 was fabricated in the same manner as in Example 3, except that the PAN content in the forming material was 10% by mass and the LiTFSI content was 20% by mass (i.e., the LiTFSI content was set to 200 parts by mass relative to 100 parts by mass of PAN), and the average thickness of the second layer was as shown in Table 4. In other words, in Example 7, the PAN content (mixing amount 1) relative to the total content of PAN and LiTFSI was set to 33% by mass and the LiTFSI content (mixing amount 2) was set to 67% by mass. Note that the mixing amount 1 and mixing amount 2 in Example 7 are expressed rounded to the first decimal place.

[0191] [Comparative Example 4] A storage element for Comparative Example 4 was fabricated in the same manner as in Example 3, except that LiTFSI was not used as the forming material and the average thickness of the second layer was as shown in Table 4.

[0192] (Initial charge / discharge 3) Initial charging and discharging were performed on the energy storage elements obtained from Examples 3 to 7 and Comparative Example 4 in the same manner as in Initial Charging and Discharging 1.

[0193] (Charge-discharge cycle test 3) For each energy storage element after the initial charge-discharge cycle 3, a charge-discharge cycle test was performed in the same manner as in charge-discharge cycle test 1.

[0194] (Measurement of the average thickness of lithium dendrites deposited after 3 charge-discharge cycle tests) The average thickness of lithium dendrites deposited after charge-discharge cycle test 3 in Examples 3 to 7 and Comparative Example 4 was measured in the same manner as described above for measuring the average thickness of the dendrites. The results are shown in Table 4. Table 4 also shows the results for Comparative Examples 1 and 3 and Example 1 described above.

[0195] [Table 4]

[0196] As shown in Table 4, even when the second layer contains a PAN-based lithium-ion conductive polymer, Examples 3 to 7, which have both a first and second layer, showed suppressed dendrite growth compared to Comparative Examples 1 and 3, which lacked at least one of the first and second layers. Furthermore, Examples 3 to 7, which have a second layer containing a lithium salt, showed suppressed dendrite growth compared to Comparative Example 4, which has a second layer without a lithium salt. In addition, as shown in Examples 3 to 5, when the lithium salt content is small compared to the PAN content, it was shown that the greater the lithium salt content, the more suppressed the dendrite growth tended to be. The reason for this is not entirely clear, but it is presumed that the lithium ion conductivity of the second layer is improved by the inclusion of a PAN-based lithium-ion conductive polymer and a lithium salt, resulting in suppressed dendrite growth. Furthermore, a comparison between Example 3 and Example 1 showed that dendrite growth was suppressed more effectively in Example 1, which has a second layer containing a PVC-based lithium-ion conductive polymer, than in Example 3, which has a second layer containing a PAN-based lithium-ion conductive polymer, even with a small amount of lithium salt. Considering these results, and the fact that PVC-based lithium-ion conductive polymers are less prone to swelling of non-aqueous electrolytes than PAN-based lithium-ion conductive polymers, as will be discussed later, it can be reasonably inferred that even in energy storage elements having a second layer containing a PVC-based lithium-ion conductive polymer, dendrite formation is suppressed more when the second layer contains a lithium salt than when it does not.

[0197] [Test Example 7] The forming material was prepared in the same manner as in Comparative Example 4 described above. The obtained forming material was coated onto a glass substrate using the doctor blade method, air-dried and then dried under reduced pressure. After that, it was punched out into a 20 mm diameter disc to form the second layer for the non-aqueous electrolyte swelling test of Test Example 7. The average thickness of this second layer was set as shown in Table 5. The obtained second layer of Test Example 7 was subjected to the non-aqueous electrolyte swelling test.

[0198] [Test Examples 8 to 12] A second layer for the non-aqueous electrolyte swelling test of Test Example 8 was formed in the same manner as in Test Example 7, except that the forming material prepared in the same manner as in Example 3 described above was set to the average thickness shown in Table 5. A second layer for the non-aqueous electrolyte swelling test of Test Example 9 was formed in the same manner as in Test Example 7, except that the forming material prepared in the same manner as in Example 4 described above was set to the average thickness shown in Table 5. A second layer for the non-aqueous electrolyte swelling test of Test Example 10 was formed in the same manner as in Test Example 7, except that the forming material prepared in the same manner as in Example 5 described above was set to the average thickness shown in Table 5. A second layer for the non-aqueous electrolyte swelling test of Test Example 11 was formed in the same manner as in Test Example 7, except that the forming material prepared in the same manner as in Example 6 described above was set to the average thickness shown in Table 5. A second layer for the non-aqueous electrolyte swelling test of Test Example 12 was formed in the same manner as in Test Example 7, except that the forming material prepared in the same manner as in Example 7 described above was set to the average thickness shown in Table 5. The obtained second layers of Test Examples 8 to 12 were subjected to the non-aqueous electrolyte swelling test.

[0199] [Test Example 13] The forming material was prepared in the same manner as in Example 3, except that LiDFP was used instead of LiTFSI as the lithium salt. Using this forming material, the second layer for the non-aqueous electrolyte swelling test of Test Example 13 was formed in the same manner as in Test Example 7, except that the average thickness was set as shown in Table 5. The obtained second layer of Test Example 13 was subjected to the non-aqueous electrolyte swelling test.

[0200] [Test Example 14] The forming material was prepared in the same manner as in Example 4, except that LiDFP was used instead of LiTFSI as the lithium salt. Using this forming material, the second layer for the non-aqueous electrolyte swelling test of Test Example 14 was formed in the same manner as in Test Example 7, except that the average thickness was set as shown in Table 5. The obtained second layer of Test Example 14 was subjected to the non-aqueous electrolyte swelling test.

[0201] [Test Example 15] Using the forming material prepared in the same manner as in Example 1 described above, a second layer for the non-aqueous electrolyte swelling test of Test Example 15 was formed in the same manner as in Test Example 7, except that the average thickness was set as shown in Table 5. The obtained second layer of Test Example 15 was subjected to the non-aqueous electrolyte swelling test.

[0202] (Non-aqueous electrolyte swelling test) (1) Preparation of non-aqueous electrolytes for testing FEC and DMC were used as non-aqueous solvents. Then, LiPF6 was added at a volume ratio of 30:70 to a mixed solvent containing FEC and DMC. 3 The solution was dissolved at the specified concentration, and PRS was further mixed into this solution as an additive at a concentration of 2% by mass to prepare a non-aqueous electrolyte for testing. (2) Evaluation of the degree of swelling For each of the second layers obtained in Test Examples 7 to 15, a non-aqueous electrolyte swelling test was performed as follows. First, the mass A (g) of the obtained second layer before non-aqueous electrolyte swelling was measured. Then, 0.2 mL of the above-mentioned test non-aqueous electrolyte was dropped onto the second layer and allowed to stand in a sealed container for 24 hours to allow the non-aqueous electrolyte to swell the second layer. After standing, the second layer was removed from the sealed container, and any excess non-aqueous electrolyte adhering to the surface of the removed second layer was removed in a manner that would not affect the measurement results. Then, the mass B (g) of the second layer after non-aqueous electrolyte swelling was measured. The mass increase (g) of the second layer due to the non-aqueous electrolyte swelling test was calculated by subtracting the mass A before non-aqueous electrolyte swelling from the mass B after non-aqueous electrolyte swelling, as shown in Equation 1 below. Furthermore, the degree of non-aqueous electrolyte swelling (mass %) of the second layer was calculated by calculating the ratio (percentage) of the mass B after non-aqueous electrolyte swelling to the mass A before non-aqueous electrolyte swelling, as shown in Equation 2 below. The results are shown in Table 5. Mass increase in the second layer (g) = Mass B - Mass A ... 1 Swelling degree of non-aqueous electrolyte in the second layer (mass%) = (mass B / mass A) × 100 ... 2

[0203] [Table 5]

[0204] As shown in Table 5, the second layer containing PAN tended to swell less in the non-aqueous electrolyte compared to the second layer containing PVC. In the second layer containing PAN, as in Test Examples 8 to 10, when the lithium salt content was small compared to the PAN content, the amount of swelling of the non-aqueous electrolyte tended to increase as the lithium salt content increased. Generally, it is thought that the greater the amount of swelling of the non-aqueous electrolyte, the more likely dendrites are to form. However, as is clear from the results in Tables 4 and 5 above, in the second layer containing PAN, when the lithium salt content was small compared to the PAN content, although the amount of swelling of the non-aqueous electrolyte increased relatively as the lithium salt content increased relatively, the formation of dendrites tended to be reduced compared to the second layer with a relatively small lithium salt content. The reason for this is not entirely clear, but it is presumed that the second layer containing PAN is a layer in which the amount of swelling of the non-aqueous electrolyte is relatively small compared to the second layer containing PVC, while also being a layer with relatively low lithium ion conductivity, and that this relatively small lithium ion conductivity was improved by the lithium salt.

[0205] The results above demonstrate that dendrite growth is suppressed in the energy storage element. [Industrial applicability]

[0206] The present invention is suitable for various power sources, including power sources for personal computers, electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and other automobiles; power sources for aircraft such as airplanes and drones; power sources for electronic devices such as personal computers and communication terminals; and power storage power sources. In particular, this energy storage element is especially suitable for use as a power source for aircraft because it combines the extremely high mass energy density particularly required for aircraft power sources with sufficient charge-discharge cycle performance. [Explanation of Symbols]

[0207] 1. Energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 6 Positive electrode 7. Positive electrode substrate 8 Cathode active material layer 9 Separator 10 Base material layer 11 Inorganic material layer 12 Negative electrode 13. Negative electrode substrate 14 1st layer 15 2nd layer 16. First Lithium Metal Layer 17. Second Lithium Metal Layer 20 Energy storage units 30 Energy storage devices

Claims

1. An electrode body including a positive electrode, a negative electrode, and a separator, Non-aqueous electrolytes and Equipped with, The above negative electrode is, Anode substrate and A first layer containing gold, platinum, or a combination thereof is disposed directly or indirectly on the separator side of the negative electrode substrate, A second layer is disposed on the separator side of the first layer, containing a lithium-ion conductive polymer and a lithium salt, and capable of restricting the passage of the non-aqueous electrolyte. Includes, The negative electrode further comprises a lithium metal layer disposed between the negative electrode substrate and the first layer.

2. The energy storage element according to claim 1, wherein the polymer contained in the second layer is formed from a polymer material containing vinylene carbonate, acrylonitrile, or a combination thereof as monomers.

3. The energy storage element according to claim 1 or claim 2, wherein the negative electrode further comprises a lithium metal layer disposed between the first layer and the separator.

4. The above separator, A base layer and The inorganic material layer disposed on the negative electrode side of the base material layer A storage element according to claim 1 or claim 2, having the following characteristics.

5. The energy storage element according to claim 1 or claim 2, wherein the lithium salt is lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, or a combination thereof.

6. The energy storage element according to claim 1 or claim 2, wherein the electrode body is pressed in the thickness direction.

7. Preparing the positive electrode, Prepare a separator, Prepare the negative electrode, The electrode body is manufactured by stacking the above-mentioned positive electrode, the above-mentioned separator, and the above-mentioned negative electrode so that they are arranged in this order. Equipped with, Preparing the above negative electrode is A first layer containing gold, platinum, or a combination thereof is formed directly or indirectly on the separator side of the negative electrode substrate. A second layer is formed on the separator side of the first layer, which contains a lithium-ion conductive polymer and a lithium salt and is capable of restricting the passage of a non-aqueous electrolyte. A lithium metal layer is formed between the above-mentioned negative electrode substrate and the above-mentioned first layer. A method for manufacturing an energy storage element.

8. One or more energy storage elements according to claim 1 or claim 2, A restraining member that restrains one or more of the above-mentioned energy storage elements and Equipped with, An energy storage device in which the electrode body is pressed down by the restraint of the above-mentioned restraint member, causing the one or more energy storage elements to be pressed in the thickness direction of the electrode body.

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