Manufacturing methods of solid-state batteries and solid-state batteries

Abstract

This invention provides a solid-state battery with high energy density and excellent cycle characteristics, as well as a method for manufacturing the same. The method for manufacturing a solid-state battery 100 includes a positive electrode 110, a solid electrolyte 120, and a negative electrode 140, comprising: a step of preparing a negative electrode 140 without a negative electrode active material; and a layer-forming step of immersing the negative electrode 140 in a layer-forming solution containing a lithium salt and a precursor, and then forming a solid electrolyte interface layer 130 having an organic compound containing lithium and an inorganic compound containing lithium on at least one surface of the negative electrode 140 by a reduction reaction on the surface of the negative electrode 140.

Description

Technical Field

[0001] This invention relates to a method for manufacturing solid-state batteries and to solid-state batteries themselves. Background Technology

[0002] In recent years, technologies that convert natural energy such as sunlight or wind power into electrical energy have attracted much attention. Along with this, various solid-state batteries have been developed as energy storage devices that are highly safe and capable of storing a large amount of electrical energy.

[0003] Among these, secondary batteries that exhibit high voltage and high energy density by moving metal ions between the positive and negative electrodes are known to perform charging and discharging. Typically, lithium-ion secondary batteries are known. As a typical lithium-ion secondary battery, an active material capable of retaining lithium is introduced into both the positive and negative electrodes, and charging and discharging are performed by the donation and acceptance of lithium ions between the positive and negative active materials. Furthermore, as a secondary battery that does not use an active material at the negative electrode, lithium metal secondary batteries have been developed that retain lithium by depositing lithium metal on the surface of the negative electrode.

[0004] For example, Patent Document 1 discloses a high-energy-density, high-output lithium metal anode secondary battery that has a volumetric energy density exceeding 1000 Wh / L and / or a gravimetric energy density exceeding 350 Wh / kg when discharged at a rate of at least 1C at room temperature. Patent Document 1 discloses the use of an extremely thin lithium metal anode to achieve such a lithium metal anode secondary battery.

[0005] Furthermore, Patent Document 2 discloses a lithium secondary battery comprising a positive electrode, a negative electrode, a separator sandwiched between them, and an electrolyte. The negative electrode is formed by metal particles formed on a negative electrode current collector, which move from the positive electrode during charging and form lithium metal on the negative electrode current collector within the negative electrode. Patent Document 2 discloses a lithium secondary battery that solves problems caused by the reactivity of lithium metal and issues arising during assembly, thereby improving performance and lifespan.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Publication No. 2019-517722

[0009] Patent Document 2: Japanese Patent Publication No. 2019-537226 Summary of the Invention

[0010] However, when the inventors conducted a detailed study of previous solid-state batteries, including those described in the aforementioned documents, they found that at least one of the capacity density or cycle characteristics was insufficient.

[0011] For example, typical secondary batteries that charge and discharge by donating and accepting metal ions between the positive and negative electrode active materials have insufficient energy density. Furthermore, lithium metal secondary batteries, as described in the aforementioned patent documents, which retain lithium by depositing lithium metal on the negative electrode surface, are prone to dendrite formation on the negative electrode surface during repeated charge and discharge cycles, leading to short circuits and capacity reduction. As a result, their cycle performance is inadequate.

[0012] Furthermore, in lithium metal secondary batteries, methods have been developed to maintain a high voltage at the interface between the negative electrode and the separator by applying significant physical pressure to the battery in order to suppress the discrete growth of lithium metal during deposition. However, since applying such a high voltage requires a large mechanical mechanism, the overall weight and volume of the battery increase, and the energy density decreases.

[0013] The present invention was made in view of the above-mentioned problems, and its object is to provide a solid-state battery with high energy density and excellent cycle characteristics, as well as a method for manufacturing the same.

[0014] One embodiment of the present invention relates to a manufacturing method for a solid-state battery comprising a positive electrode, a solid electrolyte, and a negative electrode. The manufacturing method comprises: a step of preparing a negative electrode without a negative electrode active material; and a layer-forming step of immersing the negative electrode in a layer-forming solution comprising a lithium salt and a precursor, and then forming a solid electrolyte interface layer having an organic compound containing lithium and an inorganic compound containing lithium on at least one surface of the negative electrode by a reduction reaction occurring on the surface of the negative electrode.

[0015] When a negative electrode without a negative electrode active material is used in a solid-state battery, the energy density of the solid-state battery increases because charging and discharging occur through the deposition of metal on the surface of the negative electrode and the dissolution of the deposited metal. Furthermore, when a solid electrolyte interphase (SEI) layer is formed before assembling the solid-state battery, there is no concern about the presence of precursors for SEI layer formation in the battery. Since the amount and type of precursors are not limited, the formation of the SEI layer can be precisely controlled. Then, such a solid-state battery is charged and discharged by depositing metal on the surface of a negative electrode with a precisely controlled SEI layer and the dissolution of the deposited metal. Because the SEI layer has ionic conductivity, the surface of the negative electrode becomes a uniform reaction field, and the metal deposited on the negative electrode surface grows uniformly. That is, dendrite formation is suppressed. As a result, problems such as short circuits and capacity reduction caused by dendrites forming on the negative electrode can be suppressed, resulting in solid-state batteries with excellent cycle characteristics.

[0016] An embodiment of the present invention relates to a manufacturing method that may further include a lamination step of forming a laminate by laminating a negative electrode, a solid electrolyte, and a positive electrode forming a solid electrolyte interface layer in that order with the solid electrolyte interface layer and the solid electrolyte facing each other, and a sealing step of forming a sealed body by sealing the laminate and the electrolyte into a sealed container.

[0017] The electrolyte described above preferably contains a lithium salt but not a precursor. In this manner, since the formation of the SEI layer can be suppressed when using a solid-state battery, there is a tendency to obtain a solid-state battery with superior cycle characteristics. Furthermore, since the internal resistance of the solid-state battery is further reduced, a solid-state battery with higher energy density and superior cycle characteristics can be obtained.

[0018] The aforementioned solid-state battery is preferably a lithium secondary battery that performs charging and discharging by depositing lithium metal on the surface of the negative electrode forming a solid electrolyte interface layer and then dissolving the deposited lithium. In this manner, a solid-state battery with higher energy density can be obtained.

[0019] The aforementioned negative electrode is preferably a lithium-free electrode. In this way, since highly flammable lithium metal can be avoided during manufacturing, a solid-state battery with superior safety and manufacturability can be obtained.

[0020] Preferably, in the aforementioned solid-state battery, no lithium foil is formed between the solid electrolyte and the negative electrode forming the solid electrolyte interface layer before initial charging. In this manner, since highly flammable lithium metal can be avoided during manufacturing, a solid-state battery with superior safety and manufacturability can be obtained.

[0021] The aforementioned precursor may also be at least one selected from the group consisting of one or more metal complexes selected from the group consisting of aromatic compounds, ether compounds, ester compounds, carbonate compounds, fluorine compounds, sulfone compounds, and Sn, Bi, Zn, Se, Sb, Mg, Ca, Al, Na, As, and Co.

[0022] The aforementioned precursor may also be at least one selected from the group consisting of trimethoxybenzene, difluoroanisole, monofluorobenzene, difluorobenzene, trifluorobenzene, cumene, biphenyl, cyclohexylbenzene, diphenylpropane, terphenyl, tert-alkylbenzene, tert-butylbenzene, triphenylene, fluorinated ethylene carbonate, difluoroethylene carbonate, chlorinated ethylene carbonate, phenyl carbonate, diphenyl carbonate, vinyl ethylene carbonate, trifluoropropylene carbonate, phosphazene, and derivatives thereof.

[0023] In the above-described layer formation process, it is preferable to use a two-electrode system in which the negative electrode is used as the working electrode and an electrode with a standard electrode potential of -1.0V or less for the self-dissolution reaction is used as the counter electrode, and 0.01 mA / cm flows through the working electrode. 2 Above 2.0mA / cm 2 The following reduction current generates a reduction reaction. In this way, the formation of the SEI layer can be controlled more precisely.

[0024] The aforementioned layer-forming liquid may further contain organic solvents other than the precursor.

[0025] The content of the precursor in the aforementioned layer-forming solution is preferably 1% by mass to 100% by mass relative to the total content of components other than lithium salt in the layer-forming solution. In this manner, an SEI layer that further suppresses dendrite formation on the surface of the negative electrode can be formed.

[0026] The concentration of lithium salt in the aforementioned layer-forming solution is preferably 0.01 M to 20 M relative to the layer-forming solution. In this manner, an SEI layer that further suppresses dendrite formation on the surface of the negative electrode can be formed.

[0027] The aforementioned positive electrode can also contain positive electrode active materials.

[0028] The average thickness of the aforementioned solid electrolyte interface layer is preferably 1 nm to 500 nm. This method can further suppress the formation of dendrites on the surface of the negative electrode.

[0029] An embodiment of the present invention relates to a solid-state battery comprising a positive electrode, a solid electrolyte, and a negative electrode without a negative electrode active material. Before initial charging, a solid electrolyte interface layer comprising an organic compound containing lithium and an inorganic compound containing lithium is formed on the negative electrode.

[0030] When a negative electrode without a negative electrode active material is used, the energy density of the solid-state battery is increased because charging and discharging occur through the deposition of metal on the surface of the negative electrode and the dissolution of the deposited metal. Furthermore, before the initial charge, an SEI layer containing both an organic compound and an inorganic compound containing lithium is formed on the negative electrode, allowing for precise control of the SEI layer's formation. Then, such a solid-state battery is charged and discharged by depositing metal on the surface of the negative electrode with the precisely controlled SEI layer and dissolving the deposited metal. Because the SEI layer has ionic conductivity, the negative electrode surface becomes a uniform reaction field, and the metal deposited on the negative electrode surface grows uniformly. That is, dendrite formation is suppressed. As a result, problems such as short circuits and capacity reduction caused by dendrite formation on the negative electrode can be suppressed, resulting in excellent cycle characteristics.

[0031] The aforementioned solid-state battery is preferably a lithium secondary battery that performs charging and discharging by depositing lithium metal on the surface of the negative electrode forming a solid electrolyte interface layer and then dissolving the deposited lithium. In this manner, the energy density is further increased.

[0032] The aforementioned negative electrode is preferably a lithium-free electrode. In this way, since highly flammable lithium metal can be avoided during manufacturing, both safety and manufacturability are significantly improved.

[0033] Preferably, in the aforementioned solid-state battery, no lithium foil is formed between the solid electrolyte and the negative electrode forming the solid electrolyte interface layer before initial charging. In this manner, since highly flammable lithium metal can be avoided during manufacturing, safety and manufacturability are significantly improved.

[0034] Invention Effects

[0035] According to the present invention, a solid-state battery with high energy density and excellent cycle characteristics, as well as a method for manufacturing the same, can be provided. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a solid-state battery involved in the implementation method.

[0037] Figure 2 This is a schematic diagram illustrating the use of a solid-state battery according to an implementation method.

[0038] Figure 3 This is a flowchart illustrating the manufacturing process of a solid-state battery according to the embodiments.

[0039] Figure 4 This is a schematic diagram of one step in the manufacturing method involved in the implementation method.

[0040] Figure 5 This is a schematic diagram of the process of forming a solid electrolyte interface layer in the manufacturing method described in the embodiment. Detailed Implementation

[0041] Hereinafter, with reference to the accompanying drawings, embodiments of the present invention (hereinafter referred to as "this embodiment") will be described in detail. Furthermore, in the drawings, the same reference numerals are used to label the same elements, and repeated descriptions are omitted. Moreover, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the scale of the drawings is not limited to the scale illustrated.

[0042] Solid-state batteries

[0043] like Figure 1As shown, the solid-state battery 100 of this embodiment includes a positive electrode 110, a solid electrolyte 120, and a negative electrode 140 without a negative electrode active material. Before initial charging, a solid electrolyte interface layer (SEI layer) 130 containing an organic compound containing lithium and an inorganic compound containing lithium is formed on the negative electrode 140.

[0044] (positive electrode)

[0045] As for the positive electrode 110, there are generally no particular limitations if it is used in a solid-state battery, and known materials can be appropriately selected based on the application of the solid-state battery and the type of carrier metal. From the viewpoint of improving the stability and output voltage of the solid-state battery 100, the positive electrode 110 preferably has a positive electrode active material.

[0046] In this specification, "positive electrode active material" refers to a substance used to hold metal ions that will become charge carriers or the metal corresponding to those metal ions (hereinafter referred to as "carrier metal") at the positive electrode in the battery. In other words, it can be referred to as the host material of the carrier metal.

[0047] There are no particular limitations on the positive electrode active material; examples include metal oxides and metal phosphates. For the aforementioned metal oxides, there are no particular limitations; examples include cobalt oxide compounds, manganese oxide compounds, and nickel oxide compounds. For the aforementioned metal phosphates, there are no particular limitations; examples include iron phosphate compounds and cobalt phosphate compounds. When the carrier metal is lithium ions, typical positive electrode active materials include LiCoO2 and LiNi. x Co y Mn Z O2(x+y+z=1), LiNi x Mn y O2 (x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, FeF3, LiFeOF, LiNiOF, and TiS2. One or more of these positive electrode active materials may be used alone.

[0048] The positive electrode 110 may also contain components other than the positive electrode active material mentioned above. There are no particular limitations on such components, and examples include known conductive additives, binders, solid polymer electrolytes, and inorganic solid electrolytes.

[0049] Here, as conductive additives, carbon black, single-walled carbon nanotubes (SW-CNTs), multi-walled carbon nanotubes (MW-CNTs), carbon nanofibers, and acetylene black can also be used, for example. Furthermore, as adhesives, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), acrylic resins, and polyimide resins can also be used, for example.

[0050] The content of the positive electrode active material in the positive electrode 110 can be, for example, 50% by mass or more and 100% by mass or less relative to the overall positive electrode 110. The content of the conductive additive can be, for example, 0.5% by mass or 30% by mass or less relative to the overall positive electrode 110. The content of the binder can be, for example, 0.5% by mass or 30% by mass or less relative to the overall positive electrode 110. The combined content of the solid polymer electrolyte and the inorganic solid electrolyte can also be, for example, 0.5% by mass or 30% by mass or less relative to the overall positive electrode 110.

[0051] (negative electrode)

[0052] The negative electrode 140 does not contain a negative electrode active material. Solid-state batteries with a negative electrode containing a negative electrode active material have difficulty increasing energy density due to the presence of that active material. On the other hand, the solid-state battery 100, having a negative electrode 140 without a negative electrode active material, avoids this problem. In other words, the solid-state battery 100 of this embodiment achieves high energy density because it performs charging and discharging through the deposition of metal on the surface of the negative electrode 140 and the dissolution of that deposited metal.

[0053] In this specification, "negative electrode active material" refers to a substance used to retain a carrier metal at the negative electrode; in other words, it can be considered as the host material of the carrier metal. There are no particular limitations on the mechanism for such retention; examples include intercalation, alloying, and absorption by metal clusters.

[0054] There are no particular limitations on the negative electrode active material, and examples include carbon-based materials, metal oxides, and metals or alloys. Among the aforementioned carbon-based materials, there are no particular limitations, and examples include graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanoparticles. Among the aforementioned metal oxides, there are no particular limitations, and examples include titanium oxide compounds, tin oxide compounds, and cobalt oxide compounds. Among the aforementioned metals or alloys, there are no particular limitations if they are substances capable of alloying with a carrier metal; examples include silicon, germanium, tin, lead, aluminum, gallium, and alloys containing them.

[0055] As for the negative electrode 140, there are no particular limitations if it does not have a negative electrode active material but can be used as a current collector. Examples include metals such as Cu, Al, Li, Ni, Mg, Ti, Au, Ag, Pt, Pd, and In, alloys containing them, stainless steel, and metal oxides such as fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), and tin-doped indium oxide (ITO). One or more of the above-mentioned negative electrode materials may be used alone.

[0056] The negative electrode 140 is preferably an electrode that does not contain lithium. In this way, since highly flammable lithium metal can be avoided during manufacturing, the solid-state battery 100 is superior in both safety and manufacturability. From the same viewpoint, the negative electrode 140 is preferably Cu or a Cu-containing alloy.

[0057] (Solid electrolyte)

[0058] The solid-state battery 100 includes a solid electrolyte 120. Generally, in batteries with liquid electrolytes, the physical pressure exerted by the electrolyte relative to the negative electrode surface varies depending on the liquid's movement. On the other hand, since the solid-state battery 100 includes a solid electrolyte 120, the pressure exerted by the solid electrolyte 120 on the surface of the negative electrode 140 becomes more uniform, thus better suppressing the formation of dendrites on the surface of the negative electrode 140.

[0059] As for the solid electrolyte 120, there are generally no particular limitations if it is used in a solid-state battery, and known materials can be appropriately selected according to the application of the solid-state battery and the type of carrier metal. The solid electrolyte 120 preferably has ionic conductivity but no electronic conductivity. By having ionic conductivity but no electronic conductivity, the solid electrolyte 120 can better suppress the decrease in internal resistance of the resulting solid-state battery 100 and better suppress short circuits within the solid-state battery 100. As a result, the energy density of the solid-state battery 100 is higher, and its cycle characteristics are better.

[0060] The solid electrolyte 120 is not particularly limited, and examples include substances containing resins and lithium salts. The resin itself is not particularly limited, and examples include resins having ethylene oxide units in the main chain and / or side chains, acrylic resins, vinyl resins, ester resins, nylon resins, polysiloxanes, polyphosphonates, polyvinylidene fluoride, polymethyl methacrylate, polyamides, polyimides, aramids, polylactic acid, polyethylene, polystyrene, polyurethane, polypropylene, polybutene, polyacetal, polysulfone, and polytetrafluoroethylene. One or more of the above-mentioned resins may be used alone.

[0061] The lithium salts included in the solid electrolyte 120 are not particularly limited, and examples include LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4. One or more of the aforementioned lithium salts may be used alone.

[0062] Generally, the ratio of resin to lithium salt in a solid electrolyte is determined by the ratio of oxygen atoms in the resin to lithium atoms in the lithium salt (“Li” / “O”). In the solid electrolyte 120, the resin to lithium salt ratio is preferably adjusted to the above ratio (“Li” / “O”) of 0.02 to 0.20, more preferably 0.03 to 0.15, and even more preferably 0.04 to 0.12.

[0063] The solid electrolyte 120 may also contain components other than the aforementioned resin and lithium salt. Such components are not particularly limited, and examples include solvents and salts other than lithium salts. Salts other than lithium salts are not particularly limited, and examples include salts of Na, K, Ca, and Mg.

[0064] As a solvent, there are no particular limitations, but examples include dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, chlorinated ethylene carbonate, fluorinated ethylene carbonate, difluoroethylene carbonate, trifluoromethyl propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, trimethyl phosphate, and triethyl phosphate, etc.

[0065] The solid electrolyte 120 preferably does not contain a precursor (hereinafter simply referred to as "precursor") for the formation of the SEI layer, as described later. By not containing a precursor, the solid electrolyte 120 tends to have better cycle characteristics because the formation of the SEI layer can be suppressed when using the solid battery 100. Therefore, when the solid electrolyte 120 contains an organic solvent, it is preferable to contain an organic solvent other than the precursor. Examples of organic solvents other than the precursor include those that can be included in the layer forming liquid 510, as described later.

[0066] Furthermore, in this specification, "solid electrolyte" refers to a substance containing a gel electrolyte. There are no particular limitations on the gel electrolyte; examples include substances containing polymers, organic solvents, and lithium salts. There are no particular limitations on the polymers in the gel electrolyte; examples include copolymers of polyethylene and / or polyethylene oxide, polyvinylidene fluoride (PVDF), and copolymers of PVDF and hexafluoropropylene (HFP).

[0067] (Solid electrolyte interface layer)

[0068] Since the solid-state battery 100 forms a solid electrolyte interface layer (SEI layer) 130 containing an organic compound containing lithium and an inorganic compound containing lithium on the negative electrode 140 before initial charging, it is believed to have high energy density and excellent cycle characteristics as follows.

[0069] In conventional solid-state batteries, especially lithium-ion rechargeable batteries, an SEI layer is not formed on the negative electrode before battery assembly. In such batteries, a precursor for SEI layer formation is added to the solid electrolyte and / or electrolyte during battery assembly, and the SEI layer forms inside the battery during initial charging. In existing methods of adding precursors to the electrolyte or the like inside such batteries, it is known that unreacted precursors remain in the electrolyte or the like during initial charging, and these residual precursors affect battery performance. In particular, it is known that in solid-state batteries where unreacted precursors remain in the electrolyte or the like, the SEI layer further forms due to the residual precursors, resulting in an excessively thick SEI layer and reduced capacity. That is, solid-state batteries with unreacted precursors remaining in the electrolyte or the like suffer from poor cycle characteristics. Therefore, from the viewpoint that in conventional solid-state batteries, especially lithium-ion rechargeable batteries, no precursors remain inside the battery after initial charging, the amount and type of precursors are limited. To form a high-quality SEI layer, the amount and type of precursors need to be adjusted. As mentioned above, in existing solid-state battery manufacturing methods, limiting the amount and type of precursors makes it difficult to form a high-quality SEI layer. On the other hand, since the solid-state battery 100 forms an SEI layer 130 containing both an organic compound and an inorganic compound containing lithium on the negative electrode 140 before initial charging, it is possible to precisely control the formation of the SEI layer 130. Furthermore, since precursors can be omitted from the battery, the problem of reduced cycle performance caused by residual precursors generated in existing batteries can also be solved.

[0070] Furthermore, the solid-state battery 100 performs charging and discharging by depositing metal on the surface of the negative electrode 140, which has a precisely controlled SEI layer 130, and then dissolving the deposited metal. Since the SEI layer 130 is ion-conductive, the surface of the negative electrode 140 becomes a uniform reaction field, and the metal deposited on the surface of the negative electrode 140 grows uniformly, i.e., dendrite formation is suppressed. As a result, excellent cycle characteristics are achieved because problems such as short circuits and capacity reduction can be suppressed by forming dendrites on the negative electrode 140.

[0071] Furthermore, in the solid-state battery 100, the SEI layer 130 suppresses the reduction of components contained in the solid electrolyte 120 at the negative electrode 140, thereby suppressing the irreversible reduction of metal ions generated by such reduction and the gas generation from the decomposition of the solid electrolyte 120. As a result, the solid-state battery 100 exhibits excellent cycle characteristics. In addition, since the SEI layer 130 assists in the transport of metal ions between the negative electrode 140 and the solid electrolyte 120, the solid-state battery 100 possesses a high energy density.

[0072] SEI layer 130 contains both organic compounds and inorganic compounds containing lithium. There are no particular limitations on the organic and inorganic compounds containing lithium, as they are substances already known to be present in SEI layers. While not intended to be limited, examples of organic compounds containing lithium include lithium alkyl carbonates, lithium alkoxides, and lithium alkyl esters, while examples of inorganic compounds containing lithium include LiF, Li₂CO₃, Li₂O, LiOH, lithium borate compounds, lithium phosphate compounds, lithium sulfate compounds, lithium nitrate compounds, lithium nitrite compounds, and lithium sulfite compounds.

[0073] The average thickness of the SEI layer 130 is not particularly limited; for example, it can be 1 nm or more but less than 1000 nm, 10 nm or more but less than 800 nm, or 100 nm or more but less than 500 nm. From the viewpoint of being able to better suppress the formation of dendrites on the surface of the negative electrode 140, the average thickness of the SEI layer 130 is preferably 1 nm or more but less than 500 nm.

[0074] The solid-state battery 100, by having the structure described above, exhibits high energy density and excellent cycle characteristics as follows: First, solid-state batteries with a negative electrode containing a negative electrode active material have difficulty increasing energy density due to the presence of that material. On the other hand, the solid-state battery 100 avoids this problem because it uses a negative electrode 140 without a negative electrode active material. That is, the solid-state battery 100 achieves high energy density through charging and discharging via the deposition of metal on the surface of the negative electrode 140 and the melting of that deposited metal.

[0075] Secondly, since the solid-state battery 100 forms an SEI layer 130 containing both an organic compound and an inorganic compound containing lithium on the negative electrode 140 before initial charging, the formation of the SEI layer 130 can be precisely controlled. Furthermore, since precursors do not need to be added inside the battery, the problem of reduced cycle performance caused by residual precursors generated in existing batteries can also be solved.

[0076] Third, the solid-state battery 100 performs charging and discharging by depositing metal on the surface of the negative electrode 140, which has a precisely controlled SEI layer 130, and then dissolving the deposited metal. Because the SEI layer 130 is ion-conductive, the surface of the negative electrode 140 becomes a uniform reaction field, and the metal deposited on the surface of the negative electrode 140 grows uniformly, i.e., dendrite formation is suppressed. As a result, excellent cycle characteristics are achieved because problems such as short circuits and capacity reduction caused by dendrite formation on the negative electrode 140 can be suppressed.

[0077] Fourth, because the solid-state battery 100 has a solid electrolyte 120, the pressure applied from the solid electrolyte 120 to the surface of the negative electrode 140 is more uniform than that of batteries using electrolyte, which can better suppress the formation of dendrites on the surface of the negative electrode 140. As a result, since problems such as short circuits and capacity reduction caused by the formation of dendrites on the negative electrode 140 can be suppressed, the cycle characteristics are excellent.

[0078] How to use solid-state batteries

[0079] exist Figure 2 The diagram illustrates one usage of the solid-state battery according to this embodiment. The solid-state battery 200 includes a positive electrode 110, a solid electrolyte 120, a solid electrolyte interface layer (SEI layer) 130, and a negative electrode 140 without a negative electrode active material. A positive current collector 210 is bonded to the positive electrode 110. A positive terminal 220 and a negative terminal 230 for connection to an external circuit are bonded to the positive current collector 210 and the negative electrode 140. The solid-state battery 200 forms the SEI layer 130 before initial charging.

[0080] The solid-state battery 200 is charged between the positive terminal 220 and the negative terminal 230 by applying a voltage such that a current flows from the negative terminal 230 to the positive terminal 220 through an external circuit. During charging, a carrier metal is deposited at the interface between the negative electrode 140 and the solid electrolyte interphase (SEI) layer 130 and / or the interface between the SEI layer 130 and the solid electrolyte 120. The deposited carrier metal is inhibited from growing into dendrites due to the influence of the SEI layer 130, typically growing on a thin film.

[0081] Regarding the solid-state battery 200 after charging, when the positive terminal 220 and the negative terminal 230 are connected, the solid-state battery 200 discharges. This discharges due to the precipitation and dissolution of carrier metals at the interface between the negative electrode 140 and the solid electrolyte interphase (SEI) layer 130 and / or at the interface between the solid electrolyte interphase (SEI) layer 130 and the solid electrolyte 120.

[0082] [Solid-state battery manufacturing method]

[0083] The solid-state battery manufacturing method of this embodiment is a method for manufacturing a solid-state battery comprising a positive electrode, a solid electrolyte, and a negative electrode, comprising: a negative electrode preparation step, preparing a negative electrode without a negative electrode active material; and a layer formation step, after immersing the negative electrode in a layer forming solution comprising a lithium salt and a precursor, forming a solid electrolyte interface layer comprising an organic compound containing lithium and an inorganic compound containing lithium on at least one surface of the negative electrode by generating a reduction reaction on the surface of the negative electrode. Figure 1 The solid-state battery 100 shown is manufactured as follows.

[0084] (Negative electrode preparation process)

[0085] like Figure 3 As shown, firstly, the negative electrode 140 is prepared (hereinafter referred to as the "negative electrode preparation process". Step 1). The negative electrode preparation process is the process that continues to prepare the negative electrode 140 for the layer formation process (Step 2). Specifically, it may also include a process of cutting the negative electrode material into a specified size or forming it into the negative electrode 140 by punching or the like and / or a process of cleaning the negative electrode 140.

[0086] The negative electrode preparation process can also be, for example, by cleaning a metal foil (e.g., electrolytic Cu foil) with a solvent containing aminosulfonic acid (1 μm to 1 mm), then cutting it to a specified size, and then ultrasonically cleaning it with ethanol and drying it to prepare the negative electrode 140.

[0087] (Layer formation process)

[0088] Next, as Figure 4 As shown, an SEI layer 130 is formed on the negative electrode 140 (hereinafter referred to as the "layer formation process"). The layer formation process involves immersing the negative electrode 140 in a layer formation solution containing lithium salt and a precursor, and then performing a reduction reaction on the surface of the negative electrode 140, such as... Figure 4 As shown, the process involves forming an SEI layer 130 containing both an organic compound and an inorganic compound containing lithium on one side of the negative electrode 140. Thus, because the SEI layer 130 is formed before assembling the solid-state battery 100, the manufacturing method of this embodiment does not limit the amount or type of precursors used. Therefore, by appropriately adjusting the amount and type of precursors, the formation of the SEI layer 130 can be precisely controlled, and the desired physical properties can be imparted to the SEI layer 130. In particular, the SEI layer 130 formed by the layer formation process in the manufacturing method of this embodiment can further suppress the formation of dendrites on the surface of the negative electrode 140. Furthermore, since precursors can be omitted from the solid-state battery 100, the problem of reduced cycle performance caused by residual precursors generated in existing batteries can also be solved.

[0089] In the layer forming process, such as Figure 5As shown, after immersing the negative electrode 140 and the counter electrode 520 in the layer-forming solution 510, the negative electrode 140 is used as the working electrode and connected to the counter electrode 520 via a wire 530 and an electrochemical measuring device 540. An electrochemical reduction reaction is generated on the surface of the negative electrode 140 to form an SEI layer 130. By using this method, the reduction reaction on the surface of the negative electrode 140 can be precisely controlled, and the formation of the SEI layer 130 can be precisely controlled. Specifically, by appropriately adjusting the voltage applied between the negative electrode 140 and the counter electrode 520, the magnitude of the reduction current flowing through the negative electrode 140, the composition of the layer-forming solution 510, and the reaction time, the composition, density, and thickness of the formed SEI layer 130 can be precisely controlled.

[0090] The layer formation process can form the SEI layer 130 under the condition that the applied voltage between the negative electrode 140 and the counter electrode 520 is kept constant (hereinafter also referred to as "potential constant formation"), or it can form the SEI layer 130 under the condition that the reduction current flowing through the negative electrode 140 is kept constant (hereinafter also referred to as "current constant formation"), or it can combine potential constant formation and current constant formation.

[0091] In the formation of a constant potential, the applied voltage can also be determined in the following way: That is, by scanning the applied voltage, the voltage at which a reduction reaction occurs on the surface of the negative electrode 140 can be determined, and this voltage can be defined as the applied voltage. Furthermore, the range of the applied voltage can be appropriately adjusted using the counter electrode.

[0092] In the constant current formation, from the viewpoint of more precisely controlling the formation of the SEI layer 130, the reduction current is preferably 0.01 mA / cm. 2 Above 2.0mA / cm 2 The preferred value is 0.05 mA / cm. 2 Above 1.5mA / cm 2 Hereinafter, 0.1 mA / cm is further preferred. 2 Above 1.0mA / cm 2 the following.

[0093] The reaction time for the electrochemical reduction reaction is not particularly limited; it can be 5 minutes to 20 hours, 10 minutes to 10 hours, or 30 minutes to 6 hours. The reaction time can be appropriately adjusted by considering the reaction conditions of the electrochemical reduction reaction, for example, by adjusting the amount of electrons reacted (coulombic quantity). From the viewpoint of forming an SEI layer 130 that can better suppress the formation of dendrites on the surface of the negative electrode 140, the amount of electrons reacted (coulombic quantity) is preferably 0.1 C / cm. 2Above 5.0C / cm 2 The following is more preferably 0.5C / cm 2 Above 2.0C / cm 2 the following.

[0094] In the case where the SEI layer 130 is formed by constant current formation, more specifically, it can be done as follows: That is, the negative electrode 140 (e.g., an alloy containing Cu or Cu) is used as the working electrode, and an electrode with a standard electrode potential of -1.0V or less for the self-dissolution reaction (e.g., Li, K, Ca, Na, Mg, and Al) is used as the counter electrode 520, and the two are connected via an electrochemical measuring device 540 and a wire 530. The electrode is immersed in the layer forming solution 510 and a flow rate of 0.01 mA / cm² is applied. 2 Above 2.0mA / cm 2 The following stable reduction current forms an SEI layer 130 on the negative electrode 140. The electrochemical reduction reaction ends when the open voltage of the negative electrode 140 relative to the counter electrode is between 0.5V and 2.0V.

[0095] From the viewpoint of more precisely controlling the formation of the SEI layer 130, the layer formation process is preferably performed by combining constant current formation and constant potential formation. Specifically, firstly, a negative electrode 140 (e.g., an alloy containing Cu or Cu) is set as the working electrode, and an electrode with a standard electrode potential of -1.0V or less for the self-dissolution reaction (e.g., Li, K, Ca, Na, Mg, and Al) is used as the counter electrode 520. The two are connected via an electrochemical measuring device 540 and a wire 530. After immersing the electrode in the layer forming solution 510, the open voltage is monitored and a current of 0.01 mA / cm is applied. 2 Above 2.0mA / cm 2 The following is a stable reduction current. After confirming that the SEI layer formation reaction has started, immediately switch to constant potential mode and maintain the open voltage for a period of 5 to 10 minutes, 10 to 8 minutes, 30 to 6 minutes, or 1 to 5 minutes to allow the SEI layer to form.

[0096] Furthermore, the occurrence of the SEI layer formation reaction can be confirmed using the monitored open-circuit voltage as a reference. When a reduction current flows to the working electrode in constant-current mode, the open-circuit voltage decreases sequentially, but the decrease slows down when the SEI layer formation reaction begins. Therefore, by monitoring the open-circuit voltage and identifying the point where this decrease becomes slower as the point at which the SEI layer formation reaction begins, the open-circuit voltage at that point can be used in constant-potential mode.

[0097] As a precursor used in the layer formation process, there is no particular limitation if it is a known precursor capable of forming an SEI layer 130 having both an organic compound containing lithium and an inorganic compound containing lithium. From the viewpoint of forming an SEI layer 130 that can better suppress the formation of dendrites on the surface of the negative electrode 140, the precursor is preferably at least one selected from the group consisting of aromatic compounds, ether compounds, ester compounds, carbonate compounds, fluorine compounds, sulfone compounds, and metal complexes of one or more of Sn, Bi, Zn, Se, Sb, Mg, Ca, Al, Na, As, and Co. From the same viewpoint, the precursor can be at least one selected from the group consisting of trimethoxybenzene, difluoroanisole, monofluorobenzene, difluorobenzene, trifluorobenzene, cumene, biphenyl, cyclohexylbenzene, diphenylpropane, tert-butylbenzene, tert-alkylbenzene, tert-butylbenzene, triphenylene, fluorinated ethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, phenyl carbonate, diphenyl carbonate, vinyl ethylene carbonate, trifluoropropylene carbonate, phosphazene, and derivatives thereof. From the same viewpoint, the precursor is more preferably fluorinated ethylene carbonate (FEC), fluorobenzene (FBZ), biphenyl (BPY), or diphenylethane (BPE).

[0098] The layer-forming liquid 510 may further contain organic solvents other than the aforementioned precursors. There are no particular limitations on such organic solvents other than precursors; examples include chlorinating solvents, brominating solvents, and iodizing solvents. Furthermore, organic solvents other than precursors may include substances from ether organic solvents, ester organic solvents, carbonate organic solvents, and amide organic solvents that are not equivalent to the aforementioned substances as precursors.

[0099] The content of the precursor in the layer forming solution 510 is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 15% by mass or more, relative to the total components of the layer forming solution 510 excluding lithium salt. With the precursor content within the above range, a SEI layer 130 that further suppresses dendrite formation on the surface of the negative electrode 140 can be formed. Furthermore, the upper limit of the precursor content in the layer forming solution 510 relative to the total components of the layer forming solution 510 excluding lithium salt is not particularly limited; for example, it can be 100% by mass, 90% by mass, or 80% by mass.

[0100] The concentration of lithium salt in the layer forming solution 510 is preferably 0.01M to 20M or less relative to the overall layer forming solution 510, more preferably 0.1M to 15M or less, and even more preferably 0.5M to 10M or less. By keeping the lithium salt concentration within the above range, it is possible to form an SEI layer 130 that better suppresses the formation of dendrites on the surface of the negative electrode 140.

[0101] (Preparation and lamination process of positive electrode and solid electrolyte)

[0102] Next, as Figure 3 As shown, the positive electrode 110 is prepared (step 3). The method for manufacturing the positive electrode 110 is not particularly limited to the method described above. For example, a positive electrode mixture obtained by mixing a positive electrode active material, a known conductive additive, and a known binder can be coated onto one side of a metal foil (e.g., Al foil) with a thickness of 5 μm to 1 mm and then formed by stamping. Alternatively, a commercially available positive electrode for solid-state batteries can be used.

[0103] In addition, such as Figure 3 As shown, a solid electrolyte 120 is prepared (step 3). The method for manufacturing the solid electrolyte 120 is not particularly limited; for example, it can be as follows: A resin currently used in solid electrolytes (e.g., the resin described above that can be included in the solid electrolyte 120) and a lithium salt as described above are dissolved in an organic solvent. The resulting solution is cast onto a molding substrate to a predetermined thickness to obtain the solid electrolyte 120. Here, the ratio of resin to lithium salt can also be determined as described above by the ratio of oxygen atoms in the resin to lithium atoms in the lithium salt (“Li” / “O”). This ratio (“Li” / “O”) is, for example, 0.02 to 0.20 or less. Furthermore, the organic solvent is not particularly limited; for example, acetonitrile can be used. The molding substrate is not particularly limited; for example, a PET film or a glass substrate can be used. The thickness of the obtained solid electrolyte 120 is not particularly limited; for example, it can be 10 μm to 100 μm or less.

[0104] Next, as Figure 3 As shown, the negative electrode 140, solid electrolyte 120, and positive electrode 110, which form the SEI layer 130 as obtained above, are laminated in this order with the SEI layer 130 facing the solid electrolyte 120 (hereinafter referred to as the "lamination process"). By including such a process, it is possible to reliably obtain... Figure 1 The solid-state battery 100 shown has a positive electrode 110, a solid electrolyte 120, an SEI layer 130, and a negative electrode 140.

[0105] (Enclosure process)

[0106] Next, as Figure 3As shown, a sealed body is obtained by sealing the laminate and electrolyte obtained in the lamination process into a sealed container, which is used as a solid-state battery 100. (Hereinafter referred to as the "sealing process". Step 5). In this way, by sealing the laminate and electrolyte together, the internal resistance of the solid-state battery 100 is further reduced, and there is a tendency to obtain a solid-state battery with higher energy density and excellent cycle characteristics.

[0107] The electrolyte used in the encapsulation process preferably contains lithium salt but not precursors. By omitting precursors in the electrolyte, further SEI layer formation can be suppressed when using the solid-state battery 100, resulting in a solid-state battery with superior cycle characteristics. Furthermore, because the electrolyte contains lithium salt, the internal resistance of the solid-state battery 100 is further reduced, leading to a solid-state battery with higher energy density and superior cycle characteristics.

[0108] The electrolyte may contain components other than lithium salts, provided that this embodiment does not impair its effectiveness. Such components are not particularly limited, but examples include organic solvents other than the precursor and salts other than lithium salts. Salts other than lithium salts are not particularly limited, but examples include salts of Na, K, Ca, and Mg. Organic solvents other than the precursor include substances that can be included in the layer-forming liquid 510.

[0109] As a sealed container in the sealing process, there are no particular limitations; examples include composite films.

[0110] [Variation Example]

[0111] The above-described embodiments are illustrative of the present invention. The present invention is not limited to these embodiments and can be modified in various ways without departing from its spirit.

[0112] For example, the solid-state battery of this embodiment can also be a bilayer solid-state battery obtained by forming SEI layers on both sides of the negative electrode during the layer formation process, having SEI layers on both sides of the negative electrode, and a positive electrode disposed on the side opposite to the negative electrode side of each SEI layer. Such a bilayer solid-state battery tends to have a higher energy density.

[0113] The solid-state battery of this embodiment can also be a solid-state secondary battery. Furthermore, the solid-state battery of this embodiment can also be a lithium secondary battery that performs charging and discharging by depositing lithium metal on the surface of the negative electrode forming the SEI layer and then dissolving the deposited lithium. From the viewpoint of effectively and reliably achieving the effects of this embodiment, the solid-state battery of this embodiment is preferably a solid-state secondary battery, and more preferably a lithium secondary battery that performs charging and discharging by depositing lithium metal on the surface of the negative electrode forming the SEI layer and then dissolving the deposited lithium.

[0114] The solid-state battery of this embodiment can also be manufactured without forming a lithium foil between the solid electrolyte and the negative electrode forming the SEI layer before initial charging. Since the solid-state battery of this embodiment does not form a lithium foil between the solid electrolyte and the negative electrode forming the SEI layer before initial charging, it is a solid-state battery with superior safety and manufacturability because highly flammable lithium metal can be avoided during manufacturing.

[0115] The reduction reaction in the layer formation step of the manufacturing method of this embodiment can also use any method known in the art. While not intended to be limiting, it can also be a reduction reaction using, for example, a reducing agent. In the case of a reduction reaction using a reducing agent in the layer formation step, after immersing the negative electrode in the aforementioned layer formation solution, an appropriate amount of reducing agent can be added to form an SEI layer on the negative electrode.

[0116] When the reduction reaction in the layer formation process is an electrochemical reduction reaction, the reaction conditions can be appropriately modified according to the desired physical properties of the SEI layer. If the reduction reaction occurs at the negative electrode, either a two-electrode system or a three-electrode system can be used.

[0117] The manufacturing method of this embodiment may also include a step for stabilizing the SEI layer or a step for cleaning the negative electrode after the layer formation step. The step for stabilizing the SEI layer is not particularly limited; examples include, for instance, immersing the negative electrode after SEI layer formation in a solution containing an organic solvent or acid. By including such a step, the manufacturing method of this embodiment tends to effectively and reliably achieve the effects of this embodiment.

[0118] The manufacturing method of this embodiment can also install terminals for connection to external circuits on the positive and negative electrodes after the lamination process. For example, metal terminals (e.g., Al, Ni, etc.) with a diameter of 10 μm to 1 mm can be bonded to one or both of the positive and negative electrodes respectively. As a bonding method, existing known methods can be used, or ultrasonic welding can be used, for example.

[0119] In the lamination process of the manufacturing method of this embodiment, multiple negative electrodes, solid electrolytes, and positive electrodes forming the SEI layer can be laminated. That is, the negative electrodes, solid electrolytes, and positive electrodes forming the SEI layer can be grouped together, and two or more groups of such groups can be laminated. In this way, a high-voltage solid-state battery can be obtained.

[0120] The manufacturing method of this embodiment may also omit the encapsulation step; that is, the laminate obtained through the lamination step can be kept as is and used as a solid-state battery. By omitting the encapsulation step, the productivity of the manufacturing method is further improved.

[0121] Furthermore, in this specification, "suppressing dendrite formation on the surface of the negative electrode" means suppressing the formation of dendritic deposits of the carrier metal on the surface of the negative electrode through the charging and discharging of the solid-state battery or such repetition. In other words, it means guiding the growth of carrier metal deposits on the surface of the negative electrode through the charging and discharging of the solid-state battery or such repetition into a non-dendritic state. Here, "non-dendritic" is not particularly limited, and typically refers to a plate-like, valley-like, or mound-like structure.

[0122] Furthermore, in this specification, "high energy density" or "high energy density" means that the battery has a high capacity per unit volume or mass, preferably 900Wh / L or above or 400Wh / kg or above, and more preferably 1000Wh / L or above or 430Wh / kg or above.

[0123] Furthermore, in this specification, "excellent cycle characteristics" means that the battery capacity exhibits a low rate of capacity reduction after a number of charge-discharge cycles conceivable in normal use. That is, it means that when comparing the initial capacity with the capacity after a number of charge-discharge cycles conceivable in normal use, the capacity after the charge-discharge cycles shows almost no reduction relative to the initial capacity. Here, "number of cycles conceivable in normal use" refers to, based on the intended use of the solid-state battery, such as 50, 100, 500, 1000, 5000, or 10000 cycles. Furthermore, "almost no reduction in capacity after charge-discharge cycles relative to the initial capacity" means, based on the intended use of the solid-state battery, for example, that the capacity after charge-discharge cycles is 65% or more, 70% or more, 75% or more, 80% or more, or 85% or more of the initial capacity.

[0124] Example

[0125] The present invention will now be described in more detail using examples and comparative examples. The present invention is not limited by the following examples.

[0126] [Example 1]

[0127] A 6 μm electrolytic Cu foil was cleaned in a solvent containing aminosulfonic acid, cut into 4.5 cm × 4.5 cm pieces, and then ultrasonically cleaned with ethanol and dried to prepare the negative electrode. Furthermore, a layer-forming solution was prepared by adding 10% by mass of fluorinated ethylene carbonate (hereinafter, also called "FEC") to a 4 M LiN(SO₂F)₂ (hereinafter also called "LFSI") solution in dimethoxyethane (hereinafter also called "DME") and mixing. Using the prepared negative electrode as the working electrode and a lithium metal foil as the counter electrode, the electrode was connected to an electrochemical measuring device. After immersing both electrodes in the prepared layer-forming solution, an SEI layer was formed on one side of the negative electrode under the following conditions. Afterward, the negative electrode with the SEI layer formed was removed from the layer-forming solution, and the solution was dried in a dry atmosphere.

[0128] (Conditions for SEI layer formation)

[0129] First, monitor the open voltage and apply 0.05 mA / cm to the working electrode in a constant current mode. 2 The reduction current. After confirming the SEI layer formation reaction, immediately switch to constant potential mode and perform SEI layer formation for 4 hours while maintaining the current open voltage.

[0130] Furthermore, confirmation of whether the SEI layer formation reaction has occurred is based on the value of the monitored open-circuit voltage. When a reduction current flows through the working electrode in constant-current mode, the open-circuit voltage decreases sequentially, but the decrease becomes slower once the SEI layer formation reaction begins. Therefore, the open-circuit voltage is monitored, and the point at which this decrease becomes gradual is taken as the point at which the SEI layer formation reaction begins, and this open-circuit voltage at that point is used in constant-potential mode.

[0131] Next, 96 parts by mass of LiNi were used as the positive electrode active material. 0.8 Co 0.15 Al 0.05 O2, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder are mixed and coated onto one side of a 12 μm Al foil and then stamped. The resulting molded body is then stamped into a size of 4.0 cm × 4.0 cm to obtain the positive electrode.

[0132] Next, ethylene oxide / ethylene glycol ether copolymer (P(EO / MEEGE)) (average molecular weight 1.5 million) and LiN(SO2F)2 (LFSI) are dissolved in acetonitrile at a ratio of 0.07, where the ratio of oxygen atoms in the resin to lithium atoms in the lithium salt (“Li” / “O”). A solid electrolyte is obtained by casting the resulting solution onto a molding substrate to a predetermined thickness.

[0133] A laminate is obtained by laminating the positive electrode, solid electrolyte, and negative electrode (forming the SEI layer) as described above in that order, with the SEI layer facing the solid electrolyte. Furthermore, after ultrasonically welding 100μm Al terminals and 100μm Ni terminals to the positive and negative electrodes respectively, the laminate is co-encapsulated with a 4M LFSI DME solution to obtain a solid-state battery.

[0134] [Example 2]

[0135] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), a mixture of ethylene carbonate (hereinafter also referred to as "EC")-methyl ethyl ketone (hereinafter also referred to as "EMC")-diethyl carbonate (hereinafter also referred to as "DEC") mixed solution of 1M LiPF6 (EC:EMC:DEC = 1:1:1 (volume ratio)) was used to add FEC to make 10% FEC.

[0136] [Example 3]

[0137] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), a mixture was obtained by adding FEC to a 1M LiBF4 EC-EMC-DEC mixed solution (EC:EMC:DEC = 1:1:1 (volume ratio)) to make FEC 10% by mass.

[0138] [Example 4]

[0139] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), a mixture obtained by adding FEC to a 1M lithium difluorooxalate borate (hereinafter also referred to as "LiDFOB") EC-EMC-DEC mixed solution (EC:EMC:DEC = 1:1:1 (volume ratio)) to make FEC 10% by mass.

[0140] [Example 5]

[0141] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), a mixture was obtained by adding fluorobenzene (hereinafter also referred to as "FBZ") to a 1M LiBF4 EC-EMC-DEC mixed solution (EC:EMC:DEC = 1:1:1 (volume ratio)).

[0142] [Example 6]

[0143] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), a mixture was obtained by adding biphenyl (hereinafter also referred to as "BPY") to a 1M LiBF4 EC-EMC-DEC mixed solution (EC:EMC:DEC = 1:1:1 (volume ratio)) in such a way that 5% FEC was added.

[0144] [Example 7]

[0145] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution of 4M LFSI (with 10% FEC added), diphenyl ethane (hereinafter also referred to as "BPE") was added to a 1M LiBF4 EC-EMC-DEC mixed solution (EC:EMC:DEC = 1:1:1 (volume ratio)) in such a way that 5% FEC was added.

[0146] [Example 8]

[0147] As the layer-forming liquid, except that instead of the DME solution containing 4M LFSI (with 10% FEC added), a mixture was obtained by adding FEC in a mixed EC-EMC-DEC solution containing 1M LiDFOB and 1M lithium bis(oxalatoborate) (hereinafter also referred to as "LiBOB") in a manner that makes FEC 10% by mass, a solid-state battery was obtained in the same manner as in Example 1.

[0148] [Example 9]

[0149] As the layer-forming liquid, a solid-state battery was obtained in the same manner as in Example 1, except that instead of the DME solution containing 4M LFSI (with 10% FEC added), the mixture was added in a mixed EC-EMC-DEC solution containing 1M LiDFOB and 1M LiSO3CF3 (LiTA) in a manner that made FEC 10% by mass.

[0150] [Comparative Example 1]

[0151] After cleaning the 6μm electrolytic Cu foil with a solvent containing aminosulfonic acid, it was cut into 4.5cm×4.5cm pieces, further ultrasonically cleaned with ethanol, and then dried to prepare the negative electrode.

[0152] Next, 96 parts by mass of LiNi were used as the positive electrode active material. 0.8 Co 0.15 Al 0.05A mixture of O2, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder is coated onto one side of a 12 μm Al foil and then stamped. The resulting molded body is then cut to a size of 4.0 cm × 4.0 cm to obtain the positive electrode.

[0153] Next, ethylene oxide / ethylene glycol ether copolymer (P(EO / MEEGE)) (average molecular weight 1.5 million) and LiN(SO2F)2 (LFSI) were dissolved in acetonitrile at a ratio of 0.07, where the ratio of oxygen atoms in the resin to lithium atoms in the lithium salt (“Li] / [O]”). By casting the resulting solution onto a molding substrate to a predetermined thickness, a solid electrolyte was obtained.

[0154] A laminate is obtained by laminating the positive electrode, solid electrolyte, and negative electrode as described above in this order. Furthermore, after ultrasonically welding 100 μm Al terminals and 100 μm Ni terminals to the positive and negative electrodes respectively, the laminate is encapsulated together with a 4 M LFSI FEC-DME mixed solution (FEC:DME = 1:9 (volume ratio)) to obtain a solid-state battery.

[0155] [Comparative Example 2]

[0156] As the electrolyte, a solid-state battery was obtained in the same manner as in Comparative Example 1, except that a DME solution of 4M LFSI was used instead of a 4M LFSI FEC-DME mixed solution (FEC:DME = 1:9 (volume ratio)).

[0157] [Evaluation of energy density and cycle characteristics]

[0158] The energy density and cycle characteristics of the solid-state batteries fabricated in the various embodiments and comparative examples are evaluated as follows.

[0159] The solid-state battery was charged at 7mA to a voltage of 4.2V, and then discharged at 7mA to a voltage of 3.0V (hereinafter referred to as "initial discharge"). Then, the cycle of charging at 35mA to a voltage of 4.2V and discharging at 35mA to a voltage of 3.0V was repeated 100 times at a temperature of 25°C. For each example, Table 1 shows the capacity obtained from the initial discharge (hereinafter referred to as "initial capacity") and the capacity obtained from the discharge after the above 100 cycles (hereinafter referred to as "capacity retention"). Furthermore, for comparison, the value of the initial capacity of Comparative Example 1 set to 100 is shown. Here, the initial capacity of Comparative Example 1 is 70mWh.

[0160] [Table 1]

[0161]

[0162] As can be seen from Table 1, compared with Comparative Example 2, in which no precursor (FEC) for SEI layer formation was added to the electrolyte inside the battery, Comparative Example 1, in which a precursor was added to the electrolyte inside the battery, showed improved cycle characteristics. However, the solid-state battery of this embodiment, in which an SEI layer was formed before battery assembly as in Example 1, showed even better cycle characteristics compared with Comparative Example 1.

[0163] Industrial applicability

[0164] The solid-state battery and its manufacturing method of the present invention have industrial applicability as energy storage devices for a wide variety of applications due to their high energy density and excellent cycle characteristics.

[0165] Explanation of reference numerals in the attached figures

[0166] 100 and 200 solid-state batteries

[0167] 110 Positive Electrode

[0168] 120 Solid Electrolyte

[0169] 130 Solid Electrolyte Interface Layer (SEI Layer)

[0170] 140 Negative electrode

[0171] 210 Positive current collector

[0172] 220 Positive Extreme Particle

[0173] 230 Negative extremes

[0174] 510 layer forming liquid

[0175] 520 pairs of electrodes

[0176] 530 wire

[0177] 540 Electrochemical Measurement Device

Claims

1. A method for manufacturing a solid-state battery, the solid-state battery comprising a positive electrode, a solid electrolyte, and a negative electrode, the manufacturing method comprising: The process of preparing a negative electrode that does not possess negative electrode active material; and After immersing the negative electrode in a layer-forming solution containing lithium salt and precursor, a layer-forming process is performed to form a solid electrolyte interface layer having an organic compound containing lithium and an inorganic compound containing lithium on at least one surface of the negative electrode by a reduction reaction.

2. The manufacturing method according to claim 1, further comprising: A process of forming a laminate by laminating the negative electrode, the solid electrolyte, and the positive electrode that form the solid electrolyte interface layer in this order, with the solid electrolyte interface layer and the solid electrolyte facing each other; and The process of forming an encapsulated body by sealing the laminate and electrolyte into a closed container.

3. The manufacturing method according to claim 2, wherein, The electrolyte contains lithium salt but not the precursor.

4. The manufacturing method according to any one of claims 1 to 3, wherein, The solid-state battery is a lithium secondary battery that is charged and discharged by depositing lithium metal on the surface of the negative electrode forming the solid electrolyte interface layer and dissolving the deposited lithium.

5. The manufacturing method according to any one of claims 1 to 3, wherein, The negative electrode is a lithium-free electrode.

6. The manufacturing method according to any one of claims 1 to 3, wherein, Before initial charging, the solid-state battery does not have a lithium foil formed between the solid electrolyte and the negative electrode that forms the solid electrolyte interface layer.

7. The manufacturing method according to any one of claims 1 to 3, wherein, The precursor is at least one selected from the group consisting of one or more metal complexes selected from the group consisting of aromatic compounds, ether compounds, ester compounds, carbonate compounds, fluorine compounds, sulfone compounds, and Sn, Bi, Zn, Se, Sb, Mg, Ca, Al, Na, As, and Co.

8. The manufacturing method according to claim 7, wherein, The precursor is at least one selected from the group consisting of trimethoxybenzene, difluoroanisole, monofluorobenzene, difluorobenzene, trifluorobenzene, cumene, biphenyl, cyclohexylbenzene, diphenylpropane, tert-butylbenzene, tert-alkylbenzene, tert-butylbenzene, triphenylene, fluorinated ethylene carbonate, difluoroethylene carbonate, chlorinated ethylene carbonate, phenyl carbonate, diphenyl carbonate, vinyl ethylene carbonate, trifluoropropylene carbonate, phosphazene, and derivatives thereof.

9. The manufacturing method according to any one of claims 1 to 3, wherein, In the layer formation process, a two-electrode system is used, in which the negative electrode is used as the working electrode and an electrode with a standard electrode potential of -1.0V or less for the self-dissolution reaction is used as the counter electrode. A flow of 0.01 mA / cm is then applied to the working electrode. 2 Above 2.0mA / cm 2 The following reduction current is used to produce the reduction reaction.

10. The manufacturing method according to any one of claims 1 to 3, wherein, The layer-forming liquid further comprises an organic solvent other than the precursor.

11. The manufacturing method according to any one of claims 1 to 3, wherein, The content of the precursor in the layer forming solution is more than 1% by mass and less than 100% by mass relative to the total content of the components in the layer forming solution other than lithium salt.

12. The manufacturing method according to any one of claims 1 to 3, wherein, The concentration of the lithium salt in the layer-forming solution is between 0.01 M and 20 M relative to the layer-forming solution.

13. The manufacturing method according to any one of claims 1 to 3, wherein, The positive electrode has a positive electrode active material.

14. The manufacturing method according to any one of claims 1 to 3, wherein, The average thickness of the solid electrolyte interface layer is between 1 nm and 500 nm.

15. A solid-state battery comprising a positive electrode, a solid electrolyte, and a negative electrode without a negative electrode active material. Prior to initial charging, a solid electrolyte interface layer comprising an organic compound containing lithium and an inorganic compound containing lithium is formed on the negative electrode.

16. The solid-state battery according to claim 15, wherein, The solid-state battery is a lithium secondary battery that is charged and discharged by depositing lithium metal on the surface of the negative electrode forming the solid electrolyte interface layer and dissolving the deposited lithium.

17. The solid-state battery according to claim 15 or 16, wherein, The negative electrode is a lithium-free electrode.

18. The solid-state battery according to claim 15 or 16, wherein, Prior to initial charging, no lithium foil was formed between the solid electrolyte and the negative electrode that forms the solid electrolyte interface layer.

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