Anode for solid-state secondary battery, and solid-state secondary battery

Abstract

Provided are: an anode for a solid-state secondary battery, contributing to the implementation of high energy density; and a solid-state secondary battery using the anode for a solid-state secondary battery. The anode for a solid-state secondary battery comprises an anode active material layer, a protective layer and an anode current collector, wherein: the anode active material layer contains an anode active material, which forms lithium and the like, and a first resin material, the first resin material including at least one resin material selected from either hydrophobic resin material group X or hydrophilic resin material group Y; the protective layer contains a second resin material and a carbon material, the second resin material including at least one resin material selected from either X, which is not included in the anode active material layer, or Y, which is not included in the anode active material layer, and the protective layer is positioned between the anode active material layer and the anode current collector; and the anode current collector contains aluminum or an aluminum alloy at least in part.

Description

Negative electrode for solid-state secondary battery and solid-state secondary battery

[0001] The present invention relates to a negative electrode for a solid-state secondary battery and a solid-state secondary battery.

[0002] Recently, solid-state rechargeable batteries using solid electrolytes have been attracting attention. To increase the energy density of these solid-state rechargeable batteries, cathode technologies referred to as anode-free or anode-less are being proposed.

[0003] For example, Patent Document 1 discloses an all-solid-state secondary battery and a charging method thereof in which the initial capacity of the positive electrode active material layer is greater than the initial capacity of the negative electrode active material layer. According to Patent Document 1, when the all-solid-state secondary battery is charged beyond the charging capacity of the negative electrode active material layer, lithium ions that have moved from the positive electrode to the negative electrode may be precipitated as lithium, a lithium alloy, or a lithium compound on the back side of the negative electrode active material layer or within the negative electrode active material layer. Since these can be used as active materials, the characteristics of the all-solid-state secondary battery can be improved. For example, the capacity density (capacity per unit mass) of lithium is 10 times that of graphite, which is generally used as a negative electrode active material. Therefore, by using lithium as a negative electrode active material, the all-solid-state secondary battery can be made thinner while simultaneously increasing the output.

[0004] However, when increasing the energy density of a solid-state secondary battery using such technology, side reactions may occur between the lithium, lithium alloy, or lithium compound deposited on the negative current collector during the charging process and the negative current collector. Non-patent document 1 discloses that such side reactions occur when aluminum foil or the like is used as the negative current collector of an anode-free type negative electrode. When such side reactions occur, the absorption and release of lithium present in the solid-state secondary battery become substantially impossible, which may lead to a decrease in the capacity and energy density of the solid-state secondary battery.

[0005] In order to prevent side reactions between the negative current collector and lithium, lithium alloys, or lithium compounds present in the negative electrode, a technique for forming a functional layer on the surface of the negative current collector is being considered. Patent Document 2 discloses a technique for placing an alloying prevention layer between a negative current collector made of aluminum or an aluminum alloy and a negative electrode comprising a mixed powder of negative active material particles and sulfide solid electrolyte particles. According to Patent Document 2, the alloying prevention layer consists solely of graphite. However, when the alloying prevention layer is applied to an anode-free type negative electrode, voids may exist because there is no material that hinders the diffusion of lithium between the graphite particles constituting the alloying prevention layer. Consequently, there is a risk that lithium may precipitate within the voids during the charging process, and that side reactions may occur as the precipitated lithium reaches the negative current collector.

[0006] Patent Document 1: Japanese Patent Publication No. 2019-96610

[0007] Patent Document 2: Japanese Patent Publication No. 2012-164571

[0008] Non-patent literature 1: Burak Aktekin et al., “SEI growth on Lithium metal anodes in solid-state batteries quantified with coulometric titration time analysis”, Nature Communications, October 31, 2023, No. 9, Article No. 6946

[0009] Non-patent literature 2: Naoki Suzuki et al., “Synthesis and Electrochemical Properties of I4--type Li1+2xZn1-xPS4 Solid Electrolyte”, Chemistry of Materials, published March 9, 2018, No. 30, 2236-2244 (2018)

[0010] The present invention is intended to provide a negative electrode for a solid secondary battery that contributes to the realization of high energy density, and a solid secondary battery using said negative electrode.

[0011] According to an embodiment of the present invention, a negative electrode for a solid secondary battery may be provided. The negative electrode for a solid secondary battery may include a negative active material layer, a protective layer, and a negative current collector. The negative active material layer comprises a negative active material formed from at least one selected from the group consisting of lithium, lithium alloy, and lithium compound, and a first resin material, wherein the first resin material comprises at least one selected from either a group of hydrophobic resin materials X or a group of hydrophilic resin materials Y, and the protective layer comprises a second resin material and a carbon material, wherein the second resin material comprises at least one selected from either a group of hydrophobic resin materials X not included in the negative active material layer or a group of hydrophilic resin materials Y not included in the negative active material layer, and the protective layer is disposed between the negative active material layer and the negative current collector, and the negative current collector may contain at least a portion of aluminum or an aluminum alloy.

[0012] The protective layer may contain, for every 100 parts by mass of the total content of the materials constituting the protective layer, 30 parts by mass or more and 99 parts by mass or less of the second resin material, and 1 part by mass or more and 70 parts by mass or less of the carbon material.

[0013] The above hydrophobic resin material group X may be a resin material group consisting of polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF / HFP), and polytetrafluoroethylene (PTFE).

[0014] The above hydrophilic resin material group Y may be a resin material group consisting of carboxymethylcellulose (CMC) or its salt, polyacrylamide (PAM) or its salt, polyethylene oxide (PEO) or its salt, polyvinylpyrrolidone (PVP) or its salt, and polyacrylic acid (PAA) or its salt.

[0015] The film thickness of the above protective layer may be 0.5 μm or more and 10 μm or less.

[0016] The above-mentioned cathode active material may include at least one selected from the group consisting of amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium, and zinc.

[0017] The above cathode active material may include amorphous carbon.

[0018] The above-mentioned cathode active material may be a mixture of (a) amorphous carbon and (b) at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium, and zinc.

[0019] The above-mentioned cathode active material layer may contain 33 parts by mass or more and 95 parts by mass or less of amorphous carbon with respect to 100 parts by mass of the total content of the materials constituting the above-mentioned cathode active material layer.

[0020] According to an embodiment of the present invention, a solid secondary battery may be provided. The solid secondary battery may include a positive electrode, a solid electrolyte layer, and a negative electrode. The positive electrode may include a positive active material layer and a positive current collector, the solid electrolyte layer may be disposed between the positive electrode and the negative electrode, and the negative electrode may be the negative electrode for the solid secondary battery described above.

[0021] According to the present invention, a negative electrode for a solid secondary battery that contributes to the realization of high energy density, and a solid secondary battery using the negative electrode for a solid secondary battery can be provided.

[0022] FIG. 1 is a schematic cross-sectional diagram showing the schematic configuration of a solid secondary battery according to one embodiment of the present invention.

[0023] Figure 2 is an SEM image showing the cross-sectional structure of a solid-state secondary battery fabricated according to Example 1.

[0024] Figure 3 is an SEM image showing the surface condition of the negative electrode current collector of a solid-state secondary battery fabricated according to Example 1.

[0025] Figure 4 is an SEM image showing the surface condition of the negative electrode current collector of a solid-state secondary battery fabricated according to Comparative Example 1.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in the drawings below, common components are given the same reference numerals and their functions are also considered to be the same. Also, for convenience, a negative electrode for a solid secondary battery may be simply referred to as a “negative electrode.”

[0027] Solid-state secondary battery

[0028] First, with reference to FIG. 1, an example of a solid secondary battery according to the present embodiment will be described. As shown in FIG. 1, the solid secondary battery (1) may include a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30). The positive electrode (10) may include a positive current collector (11) and a positive active material layer (12). The negative electrode (20) may include a negative current collector (21), a negative active material layer (22), and a protective layer (23). The protective layer (23) is disposed between the negative current collector (21) and the negative active material layer (22). The solid electrolyte layer (30) is formed between the positive electrode (10) and the negative electrode (20) and may include a solid electrolyte. The negative electrode (20) and the solid electrolyte layer (30) formed on the negative electrode (20) are collectively referred to as an electrolyte negative electrode structure (40). In addition, the negative electrode (20) corresponds to the negative electrode for a solid secondary battery described later.

[0029] (anode)

[0030] As illustrated in FIG. 1, the positive electrode (10) may include a positive electrode current collector (11) and a positive electrode active material layer (12). The positive electrode active material layer (12) may further include a solid electrolyte. The solid electrolyte included in the positive electrode active material layer (13) may be of the same type as the solid electrolyte included in the solid electrolyte layer (30) described later, or it may not be of the same type.

[0031] The material of the positive current collector may be, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), or germanium (Ge). The positive current collector may be formed from any one of these metals, or from an alloy of two or more metals. The shape of the positive current collector may be, for example, plate-like or thin. An undercoating layer may be applied to the positive current collector. The thickness of the positive current collector is not particularly limited, but it is preferably 1 μm or more and 20 μm or less.

[0032] The positive electrode active material may be a positive electrode active material capable of reversibly absorbing and releasing lithium ions. The material of such a positive electrode active material may be, for example, a lithium salt such as lithium cobaltate (hereinafter referred to as LCO), lithium nickelate, lithium nickel cobaltate, lithium nickel cobalt aluminumate (hereinafter referred to as NCA), lithium nickel cobalt manganese (hereinafter referred to as NCM), lithium manganese, and / or lithium iron phosphate. Furthermore, the positive electrode active material may be nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide. Each of these positive electrode active materials may be used individually or in combination of two or more.

[0033] The positive electrode active material preferably comprises a lithium salt of a transition metal oxide having a layered rock salt-type structure among the lithium salts described above. Here, “layered rock salt-type structure” refers to a cubic rock salt-type structure. <111> It is a structure in which oxygen atomic layers and metal atomic layers are alternately arranged in a regular pattern, and as a result, each atomic layer forms a two-dimensional plane. The “cubic rock salt type structure” refers to a sodium chloride type structure, which is one of the crystal structures, and specifically, it refers to a structure in which face-centered cubic lattices formed by each of the cations and anions are arranged offset from each other by half the corners of the unit cell.

[0034] Lithium salts of transition metal oxides having such a layered rock salt-type structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z O2(NCM) (where 0 <x<1, 0<y<1, 0<z<1, 그리고 x+y+z=1)과 같은 삼원계 전이 금속산화물의 리튬염을 포함할 수 있다.

[0035] When the positive active material includes a lithium salt of a ternary transition metal oxide having the above-mentioned layered rock salt structure, the energy density and thermal stability of the solid secondary battery (1) can be improved.

[0036] The positive active material may be covered by a coating layer. Such a coating layer is not particularly limited as long as it is known as a coating layer for the positive active material of a solid-state secondary battery, but may be, for example, Li2-ZrO2.

[0037] When the positive electrode active material is formed from a lithium salt of a ternary transition metal oxide such as NCA or NCM and contains nickel (Ni) as the positive electrode active material, the capacity density of the solid-state secondary battery can be increased and the leaching of metal from the positive electrode active material in the charged state can be reduced. Accordingly, the long-term reliability and cycle characteristics of the solid-state secondary battery in the charged state can be improved.

[0038] The shape of the positive electrode active material may be a particle shape, for example, such as a perfect sphere or an elliptical sphere. The particle size of the positive electrode active material is not particularly limited and may be within a range applicable to the positive electrode active material of a conventional solid-state secondary battery. The content of the positive electrode active material is not particularly limited and may be within a range applicable to the positive electrode of a conventional solid-state secondary battery.

[0039] In addition to the aforementioned positive current collector, positive active material layer, and solid electrolyte, the positive electrode may be appropriately combined with, for example, a conductivity aid, a binder, a filler, a dispersant, and an ion conductivity aid.

[0040] The conductivity aid may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon nanofiber, VGCF (registered trademark, product of Resonac), carbon nanotube, graphene, carbon fiber, or metal powder. The binder may be, for example, styrene butadiene copolymer (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or polyethylene (PE). The filler, dispersant, and ion conductivity aid may be known materials generally used in electrodes of solid-state secondary batteries.

[0041] (cathode)

[0042] As illustrated in FIG. 1, the negative electrode (20) may include a negative electrode current collector (21), a negative electrode active material layer (22), and a protective layer (23). The protective layer (23) may be disposed between the negative electrode active material layer (22) and the negative electrode current collector (21). Preferably, the protective layer (23) may be disposed only between the negative electrode active material layer (22) and the negative electrode current collector (21). A secondary battery having a so-called anode-free type (where lithium is deposited in the charged state) negative electrode generally has a high energy density, but due to the high reactivity of lithium deposited on the negative electrode current collector, side reactions between the negative electrode current collector and lithium may occur, which may result in a decrease in the energy density of the secondary battery. The negative electrode (20) according to the present embodiment may have a protective layer (23) disposed between the negative electrode current collector (21) and the negative electrode active material layer (22). Specifically, the negative electrode active material layer (22) may include a first resin material, and the protective layer (23) may include a second resin material. Here, the first resin material and the second resin material exhibit different properties. That is, one of the first resin material and the second resin material may exhibit hydrophilicity, and the other may exhibit hydrophobicity. Accordingly, when at least one selected from the group consisting of lithium, lithium alloy, and lithium compound (hereinafter, these may be summarized and simply referred to as “lithium, etc.”) is deposited between the negative electrode active material layer (22) and the protective layer (23) during the charging process of the solid secondary battery (1), the adhesion state between the negative electrode active material layer (22) and the protective layer (23) can be easily resolved. Therefore, lithium, etc. can be deposited uniformly. As a result, the protective layer (23) can sufficiently suppress side reactions between lithium, etc. and the negative electrode current collector (21), and as a result, can provide a negative electrode (20) that contributes to the realization of high energy density. The lithium alloy may be, for example, a Li-Au alloy, a Li-Pt alloy, a Li-Pd alloy, a Li-Si alloy, a Li-Ag alloy, a Li-Al alloy, a Li-Bi alloy, a Li-Sn alloy, a Li-Mg alloy, or a Li-Zn alloy.Lithium compounds can be, for example, lithium carbide.

[0043] The cathode current collector contains at least a portion of aluminum or an aluminum alloy. The material of the cathode current collector may be aluminum or an aluminum alloy. Aluminum or an aluminum alloy has high utility value because it is flexible, lightweight, relatively easy to handle, and low-cost. The shape of the cathode current collector may be, for example, plate-like or thin. The thickness of the cathode current collector is not particularly limited, but it is preferably 1 μm or more and 20 μm or less.

[0044] Since the negative electrode active material layer (22) contains a negative electrode active material that forms lithium, etc., lithium, etc. is deposited on the negative electrode during the charging process, contributing to the realization of high energy density. At this time, the protective layer (23) described later is placed between the negative electrode active material layer and the negative electrode current collector, thereby suppressing the diffusion of lithium, etc., deposited on the negative electrode during the charging process to the negative electrode current collector. As a result, side reactions that may occur between the lithium, etc., deposited on the negative electrode and the negative electrode current collector are suppressed, thereby suppressing the decrease in high energy density. Hereinafter, this function is referred to as the “current collector protection function.”

[0045] In addition to the negative electrode active material, the negative electrode active material layer (22) may further include a first resin material. Here, the first resin material may include at least one selected from either the hydrophobic resin material group X or the hydrophilic resin material group Y. By selecting the negative electrode active material layer from a resin material group exhibiting one of these properties, the surface of the protective layer of the negative electrode active material layer can be stabilized. The resin material included in the first resin material may be used alone within the same resin group or may be used in combination of two or more.

[0046] Hydrophobic resin material group X is a group of resin materials composed of hydrophobic resin materials such as, for example, polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF / HFP), and polytetrafluoroethylene (PTFE).

[0047] Hydrophilic resin material group Y is a group of resin materials that exhibit hydrophilicity, such as carboxymethylcellulose (CMC) or its salt, polyacrylamide (PAM) or its salt, polyethylene oxide (PEO) or its salt, polyvinylpyrrolidone (PVP) or its salt, and polyacrylic acid (PAA) or its salt. The form of the salt may be, for example, a lithium salt, a sodium salt, a potassium salt, or an ammonium salt.

[0048] The content of the first resin material is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the total content of the materials constituting the negative electrode active material layer, and more preferably 3 parts by mass or more and 15 parts by mass or less.

[0049] The cathode active material preferably comprises at least one selected from the group consisting of, for example, amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium, and zinc, and more preferably comprises amorphous carbon. The cathode active material may be a mixture of (a) amorphous carbon and (b) at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium, and zinc. Here, examples of amorphous carbon may be carbon black such as acetylene black, furnace black, and Ketjen black, or graphene. These cathode active materials are preferably in the form of, for example, particles, and their primary particle size is preferably 4 μm or less, more preferably 300 nm or less. Here, the primary particle size of the cathode active material may be, for example, a median diameter (so-called D50) measured using a laser particle size distributer.

[0050] When the negative electrode active material contains amorphous carbon, the negative electrode active material layer (22) preferably contains 33 parts by mass or more and 95 parts by mass or less of amorphous carbon with respect to 100 parts by mass of the total content of the materials constituting the negative electrode active material layer, and more preferably contains 50 parts by mass or more and 80 parts by mass or less of amorphous carbon. By adjusting the content of amorphous carbon included in the negative electrode active material, lithium, etc., becomes more uniformly precipitated at the negative electrode during the charging process.

[0051] In the negative electrode active material layer (22), additives used in conventional solid secondary batteries, such as fillers or dispersants, may be appropriately incorporated. Insulating fillers may be, for example, styrene butadiene copolymer (SBR). Dispersants may be known materials generally used in electrodes of solid secondary batteries.

[0052] The thickness of the negative electrode active material layer (22) is not particularly limited, but it is preferable that it be 1 μm or more and 20 μm or less. If the thickness of the negative electrode active material layer (22) is 1 μm or more and 20 μm or less, the increase in the resistance value of the negative electrode active material layer can be suppressed, thereby maintaining the characteristics of the solid secondary battery. The thickness of the negative electrode active material layer can be determined by observing the cross-section after assembling and press-molding the solid secondary battery using a scanning electron microscope (SEM).

[0053] The protective layer (23) may include a second resin material. The second resin material includes at least one selected from either a group of hydrophobic resin materials X that is not included in the negative electrode active material layer (22) or a group of hydrophilic resin materials Y that is not included in the negative electrode active material layer (22). Thus, the resin material included in the second resin material is selected from a group of resin materials that is different from the first resin material among the group of hydrophobic resin materials X or the group of hydrophilic resin materials Y (i.e., a group of resin materials that is not included in the negative electrode active material layer (22) in terms of either hydrophilicity or hydrophobicity). Accordingly, when lithium, etc. is precipitated between the negative electrode active material layer (22) containing the first resin material that exhibits one of hydrophilicity or hydrophobicity and the protective layer containing the second resin material that exhibits the other of hydrophilicity or hydrophobicity during the charging process, the adhesive force between the negative electrode active material layer (22) and the protective layer (23) is relaxed, and the adhesive state can be easily resolved. As a result, lithium and the like are uniformly deposited between the negative electrode active material layer (22) and the protective layer (23) during the charging process, thereby suppressing the occurrence of a short circuit. The resin material included in the second resin material may be used alone from the same resin group, or two or more may be used in combination.

[0054] Since the diffusion coefficient of lithium ions within the second resin material is small, side reactions that may occur between lithium deposited on the negative electrode and the negative electrode current collector are suppressed, thereby suppressing the decrease in energy density. Since there is a trade-off relationship between the characteristics of the secondary battery and the aforementioned current collector protection function regarding changes in the content of the second resin material, there exists a suitable range of the second resin material content. If the content of the second resin material is high, the current collector protection function tends to improve. However, since the second resin material has electrical insulation properties, it hinders the flow of current during the operation of the secondary battery, which may degrade the characteristics of the secondary battery. On the other hand, if the content of the second resin material is low, the characteristics of the secondary battery do not degrade, but it may be difficult to sufficiently secure the current collector protection function. Therefore, it is preferable that the content of the second resin material be 30 parts by mass or more and 99 parts by mass or less with respect to 100 parts by mass of the total content of the materials constituting the protective layer (23), and it is more preferable that it be 60 parts by mass or more and 80 parts by mass or less.

[0055] In addition to the second resin material, the protective layer (23) may further include a carbon material. The carbon material forms a conductive path necessary for normal battery operation within the protective layer (23). The carbon material is desirable to be used as a conductive filler because it has low reactivity with sulfides and is inexpensive. The carbon material is not particularly limited as long as it enhances the conductivity of the protective layer (23), but specific examples may be, for example, carbon black, natural graphite, artificial graphite, fibrous carbon, or nano carbon, and carbon black is preferred. Carbon black may be, for example, furnace black, channel black, thermal black, Ketjen black, or acetylene black. Fibrous carbon may be, for example, carbon fiber, VGCF (registered trademark, product of Resonac), or carbon nanofiber. Nano carbon may be, for example, carbon nanotubes or graphene. The carbon material may be used alone or in combination of two or more.

[0056] The content of the carbon material included in the protective layer (23) is within a suitable range depending on the trade-off relationship between the characteristics of the secondary battery and the current collector protection function. If the content of the carbon material is high, the characteristics of the secondary battery are not damaged, but the content of the resin material present in the protective layer is low, making it difficult to sufficiently secure the current collector protection function. On the other hand, if the content of the carbon material is low, the current collector protection function is improved by increasing the content of the resin material, but it may not be possible to sufficiently form the conductive path required for the operation of the secondary battery. Accordingly, the characteristics of the secondary battery may be degraded. Therefore, it is preferable that the content of the carbon material be 1 part by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the total content of the materials constituting the protective layer (23), and it is more preferable that it be 20 parts by mass or more and 40 parts by mass or less.

[0057] If the particle size of the carbon material included in the protective layer (23) is excessively large, it may be difficult to apply the protective layer (23). The primary particle size of the carbon material and the BET (Brunaure-Emmett-Teller) specific surface area are inversely proportional. The BET specific surface area of ​​the carbon material is 3m 2 / g It is desirable that it be more than 6m 2 / g It is more desirable to be above this, and 30m 2 / g It is more desirable to have an ideal value. On the other hand, if the specific surface area of ​​the carbon material is excessively large, it becomes difficult to disperse the carbon material within the slurry. For this reason, the BET specific surface area of ​​the carbon material is 5000 m² 2 It is desirable that it be less than / g.

[0058] The protective layer (23) may further include an insulating filler. The insulating filler may be, for example, polypropylene (PP). If the content of the second resin material is less than the content of the carbon material and the second resin material is selected from the group of hydrophilic resin materials, the conductivity of the protective layer (23) may be excessive, and the characteristics of the secondary battery may become unstable. Therefore, the content of the insulating filler may be 0 parts by mass or more and 69 parts by mass or less, and 20 parts by mass or more and 65 parts by mass or less, with respect to 100 parts by mass of the total content of the materials constituting the protective layer (23).

[0059] Since the protective layer (23) does not contain an active material, it is composed of an inactive material. Therefore, the smaller the thickness of the protective layer (23), the higher the volumetric energy density of the secondary battery can be. As described above, the current collector protection function is a function that suppresses the diffusion of lithium, etc., which is deposited on the negative electrode during the charging process, to the negative electrode current collector, and there is a positive correlation between the current collector protection function and the thickness of the protective layer (23). Therefore, the thicker the protective layer, the higher the current collector protection function can be. Since there is a trade-off relationship between the volumetric energy density of the secondary battery and the current collector protection with respect to the change in the thickness of the protective layer (23), there is a suitable range for the thickness of the protective layer (23). Therefore, it is preferable that the thickness of the protective layer (23) be 0.5 μm or more and 10 μm or less, and more preferable that it be 2 μm or more and 8 μm or less. In this way, by appropriately controlling the thickness of the protective layer (23), the volumetric energy density of the secondary battery and the current collector protection function can be achieved.

[0060] (Solid electrolyte layer)

[0061] As shown in FIG. 1, a solid electrolyte layer (30) is disposed between the positive electrode (10) and the negative electrode (20) (specifically, between the positive active material layer (12) and the negative active material layer (22)). The solid electrolyte layer (30) contains a solid electrolyte capable of moving ions.

[0062] The solid electrolyte is composed of, for example, a sulfide-based solid electrolyte material (hereinafter referred to as a sulfide-based solid electrolyte material). The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element such as I, Br, Cl, etc.), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are defined numbers, Z is any one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, or Li2S-SiS2-Li p MO q (p and q are integers, and M can be any one of P, Si, Ge, B, Al, Ga, or In). The solid electrolyte may be one material selected from these sulfide-based solid electrolyte materials, or two or more materials may be used.

[0063] The solid electrolyte is preferably composed of a sulfide solid electrolyte material containing sulfur (S), phosphorus (P), and lithium (Li), specifically Li2S-P2S5, in particular Li2S-P2S5-LiCl. It is more preferable to be composed of a sulfide-based solid electrolyte material. When a sulfide-based solid electrolyte material containing Li2S-P2S5 is used, the molar ratio of Li2S and P2S5 may be in the range of, for example, Li2S:P2S5 = 50:50 to 90:10.

[0064] Solid electrolytes can be in an amorphous or crystalline state. Alternatively, solid electrolytes can be in a mixed state of amorphous and crystalline.

[0065] The solid electrolyte layer may further include a binder. The material of the binder may be, for example, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or a polyacrylic acid ester-based resin. The material of the binder may be the same as or different from the material constituting the binder in the positive electrode active material layer.

[0066] Although not specifically limited, from the perspective of improving energy density, it is preferable that the thickness of the solid electrolyte layer be 500 μm or less, and more preferable that it be 100 μm or less. Meanwhile, from the perspective of suppressing internal short circuits in the secondary battery, it is preferable that the thickness of the solid electrolyte layer be 10 μm or more.

[0067] Method for manufacturing solid secondary batteries

[0068] Next, a method for manufacturing a solid secondary battery (1) according to the present embodiment will be described. The solid secondary battery (1) according to the present embodiment can be obtained by fabricating a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30), respectively, and then stacking each of the above layers.

[0069] (1) Anode manufacturing process

[0070] The manufacturing process of the anode may be a dry process or a wet process. In the case of a dry process, the anode (10) is obtained by compacting and molding a mixture of materials constituting the anode active material layer (12) into a pellet shape or by stretching it into a sheet shape. When the anode (10) is manufactured by this method, the anode current collector (11) may be pressed onto the manufactured pellet or sheet. In the case of a wet process, materials constituting the anode active material layer (12) (anode active material, binder, etc.) are added to a non-polar solvent to produce a slurry (which may be a paste). Subsequently, the slurry is applied onto the anode current collector (11) and dried to obtain a laminate. The anode (10) is manufactured by applying pressure to the laminate, for example, using hydrostatic pressure. The pressure application process may be omitted.

[0071] (2) Cathode fabrication process

[0072] A material constituting the negative electrode active material layer (22) (negative electrode active material, first resin material, etc.) is added to a polar solvent or a non-polar solvent to produce a slurry (which may be a paste) for the negative electrode active material layer. Similarly, a material constituting the protective layer (23) (carbon material, second resin material, etc.) is added to a polar solvent or a non-polar solvent to produce a slurry (which may be a paste) for the protective layer. Subsequently, the slurry for the protective layer is applied onto a negative electrode current collector (21) and dried to obtain an intermediate laminate having a protective layer (23) formed on the negative electrode current collector (21). A slurry for the negative electrode active material layer is applied onto the protective layer (23) of the intermediate laminate and dried to obtain a laminate having a negative electrode active material layer (22) formed on the protective layer (23). The laminate is cut to a predetermined size to produce a negative electrode (20). The method of applying the slurry is not particularly limited and, for example, screen printing, metal mask printing, electrostatic coating, dip coating, It may be a spray coating method, roll coating method, doctor blade method, gravure coating method, die coating method, comma coating method, or knife coating method.

[0073] (3) Solid electrolyte layer fabrication process

[0074] The solid electrolyte layer (30) can be made of a solid electrolyte formed from a sulfide-based solid electrolyte material.

[0075] First, a sulfide-based solid electrolyte material is obtained by processing the starting material using a melt quenching method or a mechanical milling method.

[0076] In the case of the melt quenching method, a sulfide-based solid electrolyte material can be produced by mixing a predetermined amount of starting materials, forming them into pellets, reacting them in a vacuum at a predetermined reaction temperature, and then quenching them. The reaction temperature of the mixture of Li2S and P2S5 is preferably 400°C to 1000°C, and more preferably 800°C to 900°C. The reaction time is preferably 0.1 hours to 12 hours, and more preferably 1 hour to 12 hours. The quenching temperature of the reactants is generally 10°C or lower, preferably 0°C or lower, and the quenching rate is generally 1°C / sec to 10000°C / sec, preferably 1°C / sec to 1000°C / sec.

[0077] In the case of the mechanical milling method, sulfide-based solid electrolyte materials can be produced by stirring and reacting starting materials using a ball mill or the like. Although the stirring speed and stirring time in the mechanical milling method are not specifically limited, a faster stirring speed can accelerate the formation rate of the sulfide-based solid electrolyte material, while a slower stirring speed can increase the conversion rate of the raw materials into the sulfide-based solid electrolyte material.

[0078] Subsequently, a particulate solid electrolyte can be produced by heat-treating the mixed raw material (sulfide-based solid electrolyte material) at a predetermined temperature and then grinding it. If the solid electrolyte has a glass transition point, it can be transformed from an amorphous state to a crystalline state through heat treatment.

[0079] Furthermore, a solid electrolyte layer (30) can be produced by forming a film using a known method, such as an aerosol deposition method, a cold spray method, and a sputtering method, on the solid electrolyte obtained by the above method. The solid electrolyte layer (30) may also be produced by pressing solid electrolyte particles. A solid electrolyte layer (30) may be produced in the form of a sheet by mixing the solid electrolyte layer (30), the solid electrolyte, a solvent, and a binder to obtain a solid electrolyte in the form of a slurry, and then applying and drying it on a substrate such as a PET film.

[0080] (4) Additive manufacturing process

[0081] A solid secondary battery (1) according to the present embodiment can be manufactured by arranging a positive electrode (10) and a negative electrode (20) with a solid electrolyte layer (30) in between and applying pressure using, for example, hydrostatic pressure. According to the present embodiment, there is no need to apply high external pressure to the solid secondary battery (1) using an end plate, and excellent discharge capacity can be obtained even if the external pressure applied to the positive electrode (10), negative electrode (20), and solid electrolyte layer (30) during use of the solid secondary battery (1) is 1 MPa or less. After manufacturing an electrolyte negative electrode structure (40) which is a laminate of a negative electrode (20) and a solid electrolyte layer (30), a positive electrode (10) can be arranged so as to overlap on the electrolyte negative electrode structure (40), and the solid secondary battery (1) can be manufactured by applying pressure such as hydrostatic pressure.

[0082] Charging Method for Solid Secondary Batteries

[0083] Next, a method for charging a solid secondary battery (1) is described. The solid secondary battery (1) is charged based on the charging capacity of the negative electrode active material layer (22). At the beginning of charging, lithium is absorbed within the negative electrode active material layer (22). When charging is performed, lithium is deposited on the rear side of the negative electrode active material layer (22) (i.e., between the protective layer (23) and the negative electrode active material layer (22)), and a metal layer (24) containing a lithium alloy or lithium compound that did not exist at the time of manufacturing is formed by this lithium. During discharge, the lithium within the negative electrode active material layer (22) and the metal layer (24) is ionized and moves toward the positive electrode (10). Thus, the solid secondary battery (1) can use lithium as a negative electrode active material. Since the protective layer (23) is placed between the negative electrode active material layer (22) and the negative electrode current collector (21), the uneven deposition of lithium, etc., can be suppressed. By doing so, short circuits and capacity reduction of the solid secondary battery (1) are suppressed, and furthermore, the characteristics of the solid secondary battery (1) can be improved.

[0084] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. The present invention includes all aspects included within the concept and claims of the present invention and may be modified in various ways within the scope of the present invention.

[0085] [Example]

[0086] Embodiments of the present invention are described below, but the present invention is not limited to these examples unless the spirit thereof is exceeded. Unless specifically stated otherwise, the processes are performed at room temperature or within the range of room temperature and 20℃±5℃.

[0087] [Example 1]

[0088] A solid secondary battery was fabricated by the following process. Each component is arranged as shown in Fig. 1.

[0089] The Production of the Bipolar

[0090] The anode (10) described below was manufactured by a dry method in a dry room set to a dew point of -60°C. LiNi as the anode active material 0.8 Co 0.15 Mn 0.05 O2 (NCM) was prepared. Li2-ZrO2 was coated onto the positive active material according to the method described in Non-Patent Literature 2. Li6PS5Cl, an Argyrodite-type crystal, was prepared as the solid electrolyte. Polytetrafluoroethylene (Teflon (registered trademark) binder manufactured by DuPont) was prepared as the binder. Carbon nanofiber (CNF) was prepared as the conductivity aid. Subsequently, a mixture was prepared by mixing the positive active material:solid electrolyte:conductivity aid:binder in a mass ratio of 85:15:3:1.5, and the mixture was stretched into a sheet shape to produce a positive sheet. By making this positive sheet into a square of about 1.7 cm and pressing it onto a positive current collector (11) made of 10 μm thick aluminum foil with a 1 μm thick undercoat layer applied to its surface, a positive (10) was produced in which a positive active material layer (12) was formed on the positive current collector (11). An aluminum tab lead was welded to the positive current collector (11) included in the positive electrode (10). The initial charging capacity of the positive electrode (charging capacity of the first cycle) was about 15 mAh for a 4.25 V charge, and the mass of the positive electrode was about 80 mg (about 240 mAh / g per mass of active material).

[0091] <Fabrication of the Cathode>

[0092] As described below, a protective layer (23) is formed on the surface of a negative current collector (21) formed of aluminum foil with a thickness of 15 μm. A negative active material layer (22) is formed on the surface of the protective layer (23) (i.e., the surface facing the positive electrode (10)).

[0093] (Construction of protective layer)

[0094] Carbon material with a nitrogen adsorption specific surface area of ​​approximately 16 m² 2Carbon black (furnace black, hereinafter referred to as “CB”) with a content of 1 / g was prepared. As a second resin material, an aqueous polyacrylamide solution (solid content concentration of 7.3 parts by mass) was prepared. As an insulating filler, an aqueous dispersion of polypropylene (hereinafter referred to as “PP”) resin fine particles (solid content concentration of 25 parts by mass) was prepared. Subsequently, 2.0g of carbon material and 128.4g of an aqueous polyacrylamide (hereinafter referred to as “PAM”) solution were weighed and placed into a stirring vessel. The stirring vessel was mounted on a rotating orbit mixer ARE-310 (THINKY) and mixed at 2000 rpm for 10 minutes. The resulting mixture was subjected to high-pressure dispersion treatment using an ultra-high pressure wet atomization device (manufactured by Yoshida Industrial Co., Ltd., “NanoVator”) to obtain an aqueous dispersion of furnace black. The solid content of the aqueous dispersion was about 10%.

[0095] Next, a separate stirring vessel was prepared, 14.0 g of an aqueous dispersion of polypropylene resin fine particles was added, and the mixture was stirred at 400 rpm using a magnetic stirrer. Then, 23.1 g of the obtained aqueous dispersion of furnace black was carefully added at a rate of about 0.5 g per second. Subsequently, the stirring vessel was mounted on a rotational mixer “ARE-310” (THINKY) and mixed at 2000 rpm for 6 minutes to obtain a protective layer in the form of a slurry (hereinafter also referred to as “protective layer slurry”). The solid content of the protective layer slurry was about 16%.

[0096] Using an applicator, the protective layer slurry obtained by the above method was applied onto a negative current collector (21) of aluminum foil having a thickness of 15 μm. By drying the aluminum foil after application in a constant temperature bath set to 80°C for 10 minutes, a protective layer (23) formed on the aluminum foil was obtained. The thickness of the protective layer (23) after drying was about 5 μm. As shown in Table 1, the mass ratio of the materials of the components included in the protective layer (23) was PP:CB:PAM = 60:28:12 (parts by mass), and the resin material:carbon material = 72:28 (parts by mass).

[0097] (Fabrication of the cathode active material layer)

[0098] Nitrogen adsorption as cathode active material, specific surface area approximately 52 m² 2CB with a DBP absorption of approximately 193 ml / 100 g and silver particles with a particle size of 60 nm were used. For example, the median diameter (so-called D50) measured using a laser particle size distribution meter was used for the silver particles. Subsequently, 3 g of CB and 1 g of silver particles were placed in a container, and 4 g of an N-methylpyrrolidone (NMP) solution containing 5 mass% of the first resin material (polyvinylidene fluoride (PVDF)) was added thereto. A slurry-type cathode active material layer (hereinafter referred to as the “cathode active material layer slurry”) was prepared by stirring the mixed solution while gradually adding a total amount of 30 g of NMP to this mixed solution. Using an applicator, a cathode active material layer slurry was applied onto the protective layer (23) described above, and by drying it in a constant temperature bath set to 80°C for 20 minutes, a cathode active material layer (22) was formed on the protective layer (23). This was cut into a rectangular shape of about 2 cm to produce a cathode (20). The produced cathode was brought into a dry room set to a dew point of -60°C and vacuum dried at 100°C for 12 hours. After vacuum drying, an aluminum tab lead was welded to the cathode current collector (21) containing the cathode (20). The mass ratio of the components contained in the cathode active material layer was CB:Ag:PVDF = 3:1:0.2 (parts by mass), and the active material:resin material = 4:0.2 (parts by mass).

[0099] <Fabrication of Solid Electrolyte Layer>

[0100] Li6PS5Cl powder was prepared as a solid electrolyte. A rubber-based binder was added to the solid electrolyte in terms of solid content, with respect to the mass of the solid electrolyte. By adding xylene and diethylbenzene to this mixture while stirring, a solid electrolyte in the form of a slurry (hereinafter referred to as “solid electrolyte slurry”) was prepared. Using an applicator, the solid electrolyte slurry was applied onto a PET (polyethylene terephthalate) film with a release-treated surface, dried on a hot plate at 40°C for 10 minutes, and then vacuum dried at 40°C for 12 hours. This was cut into a rectangular shape of approximately 2.1 cm to obtain a solid electrolyte sheet formed on the release-treated PET film. The thickness of the solid electrolyte layer after vacuum drying was approximately 65 μm.

[0101] Fabrication of Electrolyte Cathode Structure

[0102] A 3mm thick aluminum plate with a release film attached to its surface is prepared as a support material. Subsequently, the cathode (20) manufactured as described above and the solid electrolyte sheet formed on the release-treated PET film are provided on the release film attached to the aluminum plate. At this time, the surface of the cathode current collector (21) included in the cathode (20) is in contact with the surface of the release film, and the cathode active material layer (22) included in the cathode (20) is in contact with the solid electrolyte sheet. Then, they are arranged so that the contact area between the cathode active material layer (22) and the solid electrolyte sheet is maximized. To prevent this arrangement from collapsing, another release film is placed over it and secured with polyimide tape. Furthermore, these are vacuum-packed with an aluminum laminate film, immersed in a pressurized medium, and subjected to hydrostatic treatment (isotropic pressure press) at 50MPa. Afterward, the solid electrolyte layer (30) formed on the cathode (20) is produced by removing the PET film. Here, the cathode (20) and the solid electrolyte layer (30) formed on the cathode (20) are collectively referred to as an electrolyte cathode structure (40).

[0103] <Production of Solid Secondary Batteries>

[0104] An electrolyte negative electrode structure (40) is positioned so that the negative electrode (20) is below the solid electrolyte layer (30). Subsequently, an anode (10) is provided on the electrolyte negative electrode structure (40) so that the surface of the positive active material layer (12) contacts the surface of the solid electrolyte layer (30). At this time, the four sides of the electrolyte negative electrode structure (40) and the four sides of the anode (10) are arranged to be parallel so that the center of the electrolyte negative electrode structure (40) and the center of the anode (10) overlap. Subsequently, to prevent this arrangement from breaking, these are placed in an aluminum laminate film prepared as an outer body, and the tab leads of the anode (10) and the negative electrode (20) are drawn out to the outside and sealed in a vacuum, thereby producing a solid secondary battery (1). Additionally, the solid secondary battery (1) was subjected to hydrostatic pressure treatment at 490 MPa for 30 minutes. By performing this hydrostatic pressure treatment, the characteristics as a solid-state secondary battery can be significantly improved.

[0105] A solid secondary battery was placed between two stainless steel plates that were rectangular in shape with a diameter of 5.5 cm and a thickness of approximately 1 cm. Each of the two stainless steel plates had four holes drilled at the same location, and the solid secondary battery was positioned to fit inside the rectangle formed by the four holes. In this state, one bolt was passed through each of the four holes to penetrate the two stainless steel plates from the outside. Subsequently, a pressure of approximately 4 MPa was applied to the solid secondary battery by tightening the four bolts with nuts to press the two stainless steel plates from the outside.

[0106] Charge / Discharge Test

[0107] The charge-discharge characteristics of the solid-state secondary battery fabricated as described above were evaluated by the following charge-discharge test. The charge-discharge test was conducted by placing the solid-state secondary battery in a constant temperature bath at 25°C. In the first cycle, 1.5 mA (approx. 0.52 mA / cm²) was applied until the battery voltage reached 4.25 V.2 It was charged with a constant current, and then charged with a constant voltage until the battery voltage reached 4.25 V and the current became 0.26 mA. Subsequently, it was charged at 1.5 mA (approx. 0.52 mA / cm²) until the battery voltage reached 2.5 V. 2 Discharged with a constant current of ).

[0108] During the charge-discharge test, the presence or absence of a short circuit was checked. A discharge capacity of 150 mAh / g or more per unit mass of active material was evaluated as “OK,” and a discharge capacity of 150 mAh / g or more per unit mass of active material was evaluated as “NG.” The results are shown in Table 1. However, if a short circuit occurred during the charge-discharge test, the discharge capacity was not measured.

[0109] SEM observation of lithium precipitated during the charging process

[0110] After the charge / discharge test, the cross-section of the solid secondary battery was observed using a scanning electron microscope (SEM, commonly referred to as “SEM”) to confirm the precipitation of lithium. Observation and imaging were performed at a magnification of 2000x. The results are shown in FIG. 2. Additionally, from the SEM image in FIG. 2, the thickness of the negative electrode active material layer (22) was approximately 10 μm.

[0111] <Evaluation of Side Reactions Between Lithium and Cathode Current Collector>

[0112] After the charge / discharge test, the solid secondary battery was removed from the charge / discharge device, and the solid secondary battery was disassembled in a dry room and only the negative current collector (21) was removed. Then, the surface of the negative current collector (21) opposite to the surface coated with the protective layer (23) was observed using SEM. Observation and photography were performed at a magnification of 1000 times. The results are shown in FIG. 3.

[0113] <Evaluation of the Uniformity of Precipitated Lithium>

[0114] During the charge / discharge test, the charge / discharge test program was stopped when the battery was fully charged, and the solid secondary battery was removed from the charge / discharge device. Subsequently, the solid secondary battery was brought into a dry room, and the aluminum laminate film sealing the solid secondary battery was removed. The surface of the negative current collector (21) on the opposite side from the surface coated with the protective layer (23) was visually inspected.

[0115] In the above-described visual observation, if the flatness of the negative electrode current collector (21) is clearly damaged, the deposition of lithium is evaluated as non-uniform, and in other cases, it is evaluated as uniform. The results are shown in Table 1.

[0116] [Example 2]

[0117] A solid secondary battery was manufactured in the same manner as Example 1, except that the mass ratio of the components contained in the protective layer (23) was set to PAM:CB=70:30 and the insulating filler was not included, and was evaluated as described above. The results are shown in Table 1.

[0118] [Example 3]

[0119] As the first resin material and insulating filler included in the negative electrode active material layer (22), CMC with a content of 2 mass% and SBR (styrene butadiene copolymer) with a content of 3 mass% are used, respectively. PVDF is used as the second resin material included in the protective layer (23). A solid secondary battery was manufactured in the same manner as in Example 2, except that the mass ratio of the materials included in the protective layer was set to PVDF : CB = 80 : 20, and the evaluation described above was performed. The results are shown in Table 1.

[0120] [Example 4]

[0121] A solid-state secondary battery was fabricated in the same manner as in Example 1, except that an aluminum-deposited PET film was used as the material for the negative electrode current collector, and the evaluation described above was performed. The results are shown in Table 1.

[0122] [Example 5]

[0123] A solid secondary battery was fabricated in the same manner as in Example 2, except that PAA and carbon nanotubes (hereinafter also referred to as “CNT”) were used as the second resin material and carbon material included in the protective layer (23), respectively, and the above-described evaluation was performed. The results are shown in Table 1.

[0124] [Example 6]

[0125] A solid secondary battery was manufactured in the same manner as in Example 2, except that PVP and CNT were used as the second resin material and carbon material, respectively, included in the protective layer (23), and the evaluation described above was performed. The results are shown in Table 1.

[0126] [Example 7]

[0127] A solid secondary battery was manufactured in the same manner as in Example 2, except that CMC and CNT were used as the second resin material and carbon material included in the protective layer (23), respectively, and the mass ratio of the materials of the components included in the protective layer was set to CMC : CNT = 99 : 1, and the evaluation described above was performed. The results are shown in Table 1.

[0128] [Example 8]

[0129] A solid secondary battery was manufactured in the same manner as in Example 3, except that the mass ratio of the materials of the components included in the protective layer (23) was set to PVDF:CB=30:70, and the above-described evaluation was performed. The results are shown in Table 1.

[0130] [Comparative Example 1]

[0131] A solid secondary battery was manufactured in the same manner as in Example 1, except that a protective layer (23) was not formed, and the evaluation described above was performed. The results are shown in Table 1. As in FIG. 3, in order to evaluate the side reaction between lithium and the negative current collector (21), only the negative current collector (21) was removed, and the surface of the negative current collector (21) opposite to the surface facing the negative active material layer (22) was observed using SEM. The SEM image is shown in FIG. 4.

[0132] [Comparative Example 2]

[0133] A solid secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode active material layer (22) was not formed, and the evaluation described above was performed. The results are shown in Table 1.

[0134] [Comparative Example 3]

[0135] A solid secondary battery was manufactured in the same manner as in Example 2, except that PVDF was used as the first resin material included in the negative electrode active material layer (22) and the mass ratio of the materials of the components included in the protective layer (23) was set to PVDF:CB=8:92, and the above-described evaluation was performed. The results are shown in Table 1.

[0136] [Comparative Example 4]

[0137] A solid secondary battery was manufactured in the same manner as in Example 4, except that CMC with a content of 2 mass% and SBR with a content of 3 mass% were used as the first resin material and insulating filler for the negative electrode active material layer (22), respectively, and the evaluation described above was performed. The results are shown in Table 1.

[0138] [Table 1]

[0139]

[0140] As shown in Table 1, it was found that Examples 1 to 8 all had no short circuits in the charge-discharge test, possessed excellent discharge capacity, and possessed high energy density. As shown in FIG. 2, in the negative electrode for a solid secondary battery fabricated according to Example 1, it was confirmed that a metal layer (24) in which lithium is uniformly deposited is formed between the negative electrode active material layer (22) and the protective layer (23) after the charge-discharge test. Therefore, according to Examples 1 to 8, it can be seen that a solid secondary battery with high energy density can be provided by utilizing an anode-free type negative electrode technology in which lithium (at least one selected from the group consisting of lithium, lithium alloys, and lithium compounds) can be used as the active material of the negative electrode, and by providing a negative electrode for a solid secondary battery that can contribute to the realization of high energy density through a current collector protection function.

[0141] When comparing Example 1 and Comparative Example 1, it was found that Comparative Example 1, in which the protective layer (23) is not formed, has a small discharge capacity and does not possess a sufficiently high energy density. In Comparative Example 1, a side reaction occurs between the lithium deposited on the negative electrode and the aluminum foil, which is the negative electrode current collector, during the charging process, resulting in a smaller discharge capacity and a decrease in energy density. In Fig. 4, the flatness of the negative electrode current collector is lost compared to Fig. 3. From these observation results, it can be seen that side reactions of the negative electrode current collector, including the aluminum foil, can be suppressed by forming a protective layer.

[0142] When comparing Example 1 and Comparative Example 2, a short circuit occurred in Comparative Example 2, in which a negative electrode active material layer containing a negative electrode active material and a first resin material was not installed. From this, it can be seen that by forming a negative electrode active material layer, a short circuit does not occur and high energy density can be achieved.

[0143] When comparing Example 1 and Comparative Example 3, a short circuit occurred in Comparative Example 3, where hydrophobic resin materials were used as the first resin material and the second resin material, respectively. From this, by using resin materials with different properties (one exhibiting hydrophilicity and the other exhibiting hydrophobicity) as the first resin material and the second resin material, respectively, the adhesion between the negative electrode active material layer and the protective layer was easily resolved during the charging process, and lithium, etc., was uniformly precipitated, thereby suppressing the occurrence of a short circuit.

[0144] In the comparison between Example 1 and Comparative Example 4, just as in the comparison between Example 1 and Comparative Example 3, a short circuit occurred in Comparative Example 4, in which a hydrophilic resin material was used as the first resin material and a second resin material, respectively. Therefore, it appears that a short circuit occurred in Comparative Example 4 as well, due to the same phenomenon described above.

[0145] [Explanation of the symbol]

[0146] 1 Solid-state secondary battery

[0147] 10 anodes

[0148] 11 positive current collector

[0149] 12 positive electrode active material layer

[0150] 20 cathodes

[0151] 21 Cathode current collector

[0152] 22 Cathode active material layer

[0153] 23 protective layer

[0154] 24 metal layers

[0155] 30 solid electrolyte layers

[0156] 40 Electrolyte cathode structure

Claims

1. A negative electrode for a solid-state secondary battery comprising a negative electrode active material layer, a protective layer, and a negative electrode current collector, The above negative electrode active material layer comprises a negative electrode active material formed from at least one selected from the group consisting of lithium, lithium alloys and lithium compounds, and a first resin material. The first resin material comprises at least one selected from either the hydrophobic resin material group X or the hydrophilic resin material group Y, and The above protective layer comprises a second resin material and a carbon material, and The second resin material comprises at least one selected from either group of hydrophobic resin materials X not included in the negative electrode active material layer or group of hydrophilic resin materials Y not included in the negative electrode active material layer. The above protective layer is disposed between the above negative electrode active material layer and the above negative electrode current collector, and the above negative electrode current collector is a negative electrode for a solid secondary battery containing at least a portion of aluminum or an aluminum alloy.

2. In Paragraph 1, The above protective layer is a negative electrode for a solid secondary battery containing, with respect to a total content of 100 parts by mass of the materials constituting the above protective layer, 30 parts by mass or more and 99 parts by mass or less of the above second resin material, and 1 part by mass or more and 70 parts by mass or less of the above carbon material.

3. In Paragraph 1, The above hydrophobic resin material group X is a negative electrode for a solid secondary battery, comprising polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF / HFP), and polytetrafluoroethylene (PTFE).

4. In Paragraph 1, The above hydrophilic resin material group Y is a negative electrode for a solid secondary battery, which is a resin material group comprising carboxymethylcellulose (CMC) or its salt, polyacrylamide (PAM) or its salt, polyethylene oxide (PEO) or its salt, polyvinylpyrrolidone (PVP) or its salt, and polyacrylic acid (PAA) or its salt.

5. In Paragraph 1, A negative electrode for a solid secondary battery having a protective layer thickness of 0.5 μm or more and 10 μm or less.

6. In Paragraph 1, The above negative electrode active material comprises at least one selected from the group consisting of amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium, and zinc, for a solid secondary battery negative electrode.

7. In Paragraph 6, The above negative electrode active material is a negative electrode for a solid secondary battery containing amorphous carbon.

8. In Paragraph 6, The above negative electrode active material is (a) amorphous carbon, and (b) a negative electrode for a solid secondary battery that is a mixture of at least one selected from the group consisting of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, magnesium and zinc.

9. In Paragraph 6, The above negative electrode active material layer contains 33 parts by mass or more and 95 parts by mass or less of amorphous carbon with respect to 100 parts by mass of the total content of the materials constituting the above negative electrode active material layer, for a negative electrode for a solid secondary battery.

10. A solid secondary battery comprising a positive electrode, a solid electrolyte layer, and a negative electrode, The above-mentioned positive electrode includes a positive electrode active material layer and a positive electrode current collector, and The above solid electrolyte layer is disposed between the anode and the cathode, and The above-mentioned negative electrode is a solid secondary battery that is a negative electrode for a solid secondary battery as described in any one of claims 1 to 9.

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