Negative electrode material, negative electrode, lithium secondary battery, and method for manufacturing negative electrode material

Abstract

To provide a negative electrode material for a lithium secondary battery, in which the occurrence of Li dendrites is suppressed, and which therefore has improved cycle characteristics.SOLUTION: A negative electrode material is provided which is used for a negative electrode of a lithium secondary battery including a non-aqueous electrolyte, the negative electrode material comprises a first layer including lithium metal as a negative electrode active material, and a second layer disposed on at least one surface of the first layer, the second layer is made of a compound represented by the general formula MxAy (M is an element selected from the group consisting of Al, In, Mg, Ag, Si, and Sn, and A is an element selected from the group consisting of O, N, P, and F, 0.3<x / y<3), and has a thickness of 100 nm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a material for a negative electrode, a negative electrode, a lithium secondary battery, and a method for manufacturing a material for a negative electrode.

Background Art

[0002] Patent Document 1 discloses a negative electrode in which a lithium phosphate nitride is formed on the surface of a lithium metal layer. Patent Document 2 discloses a negative electrode in which an ion conductive material having a thickness of at least 0.5 μm is formed on the surface of a lithium metal layer. Patent Document 3 discloses a negative electrode in which a sulfide-based inorganic material is formed on the surface of a lithium metal layer. [Prior Art Documents] [Patent Documents] [Patent Document 1] U.S. Patent No. 5314765 [Patent Document 2] U.S. Patent No. 10461372 [Patent Document 3] U.S. Patent No. 10833360

Summary of the Invention

[0003] In a first aspect of the present invention, a material for a negative electrode is provided. The above material for a negative electrode is used, for example, for a negative electrode of a lithium secondary battery containing a non-aqueous electrolyte. The above material for a negative electrode includes, for example, a first layer containing lithium metal as a negative electrode active material. The above material for a negative electrode includes, for example, a second layer disposed on at least one surface of the first layer. In the above material for a negative electrode, the second layer is, for example, represented by the general formula M x A y (M is one element selected from the group consisting of Al, In, Mg, Ag, Si, and Sn, A is one element selected from the group consisting of O, N, P, and F, and 0.3 < x / y < 3). The second layer in the above material for a negative electrode has, for example, a thickness of 100 nm or less.

[0004] In the above material for a negative electrode, the second layer may have a thickness of less than 50 nm. In the above material for a negative electrode, A may be one element selected from the group consisting of O and N.

[0005] In a second aspect of the present invention, a negative electrode is provided. The negative electrode described above includes, for example, the negative electrode material according to the first aspect described above. The negative electrode described above includes, for example, a negative electrode current collector that holds the negative electrode material.

[0006] In the negative electrode described above, the second layer may be disposed so as to entirely cover the first layer disposed in contact with the negative electrode current collector. In the negative electrode described above, the second layer may be disposed such that a part of the second layer is in contact with the negative electrode current collector.

[0007] In a third aspect of the present invention, a lithium secondary battery is provided. The lithium secondary battery described above includes, for example, the negative electrode according to the second aspect described above. The lithium secondary battery described above includes, for example, a positive electrode. The lithium secondary battery described above includes, for example, a non-aqueous electrolyte.

[0008] In the lithium secondary battery described above, the non-aqueous electrolyte may contain a cyclic carbonate having a fluorine atom. In the lithium secondary battery described above, the ratio of the cyclic carbonate having a fluorine atom to the whole of the non-aqueous electrolyte may be 20 mol% or more and 80 mol% or less. In the lithium secondary battery described above, the cyclic carbonate having a fluorine atom may contain fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC).

[0009] In the lithium secondary battery described above, the negative electrode may contain an alloy of lithium and an element represented by M contained in the second layer after the charge and discharge of the lithium secondary battery has been carried out at least once. In the lithium secondary battery described above, the second layer may contain nitrogen as the element represented by A. In the lithium secondary battery described above, the negative electrode may contain lithium nitride after the charge and discharge of the lithium secondary battery has been carried out at least once.

[0010] In a fourth aspect of the present invention, a method for manufacturing a negative electrode used in a lithium secondary battery containing a non-aqueous electrolyte is provided. The above method has, for example, a step of preparing a first layer containing lithium metal as a negative electrode active material. The above method has, for example, a step of forming a second layer on at least one surface of the first layer. In the above method, the second layer is, for example, represented by the general formula M x A y (M is one element selected from the group consisting of Al, In, Mg, Ag, Si, and Sn, A is one element selected from the group consisting of O, N, P, and F, and 0.3 < x / y < 3.) and is composed of a compound represented by. In the above method, the second layer has, for example, a thickness of 100 nm or less.

[0011] Note that the above summary of the invention does not list all the necessary features of the present invention. Also, sub-combinations of these feature groups can also be inventions.

Brief Description of the Drawings

[0012] [Figure 1] An example of the internal structure of the storage battery 100 is schematically shown. [Figure 2] An example of the manufacturing method of the storage battery 100 is schematically shown. [Figure 3] The results of the cycle characteristic test of the symmetric cell of Example 1 are shown. [Figure 4] The results of the cycle characteristic test of the symmetric cell of Comparative Example 1 are shown. [Figure 5] The results of the cycle characteristic test of the symmetric cell of Example 2 are shown.

Modes for Carrying Out the Invention

[0013] In this embodiment, taking as an example the case where the negative electrode material used for the negative electrode of a lithium secondary battery containing a non-aqueous electrolyte includes at least a first layer and a second layer, details of the negative electrode material, the negative electrode, the lithium secondary battery, and the method for manufacturing the negative electrode material will be described. In this embodiment, the above-mentioned first layer contains lithium metal as a negative electrode active material. The above-mentioned second layer is disposed on at least one surface of the first layer. The above-mentioned second layer is composed of a compound represented by the general formula MxAy (M is one element selected from the group consisting of Al, In, Mg, Ag, Si, and Sn, A is one element selected from the group consisting of O, N, P, and F, and 0.3 < x / y < 3). Further, the above-mentioned second layer has a thickness of 100 nm or less.

[0014] According to this embodiment, since the second layer is made of an inorganic material having a specific composition and thickness, a second layer excellent in conductivity or ion conductivity can be obtained. Thereby, the overvoltage of the lithium secondary voltage during charge and discharge is suppressed. Further, according to this embodiment, since the second layer is disposed on the surface of the first layer, direct contact between the lithium metal of the first layer and the non-aqueous electrolyte is suppressed. Thereby, the reduction of the non-aqueous electrolyte by the lithium metal is suppressed. As a result, the generation of dendritic lithium (sometimes referred to as Li dendrite) during charge and discharge of the lithium secondary battery is suppressed. Further, by suppressing the generation of Li dendrite, the cycle characteristics of the lithium secondary battery are improved. For example, the cycle life of the lithium secondary battery is increased.

[0015] As described above, according to this embodiment, the performance degradation of the battery is suppressed and the stability during battery driving is improved. In particular, when the non-aqueous electrolyte contains a cyclic carbonate having a fluorine atom, the performance degradation of the battery is greatly suppressed and the stability during battery driving is greatly improved.

[0016] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

[0017] In this specification, when a numerical range is expressed as "A to B", it means A or greater and B or less. Furthermore, "substituted or unsubstituted" means "substituted with any substituent, or not substituted with any substituent." The types of substituents are not particularly limited unless otherwise specified in the specification. Furthermore, the number of substituents is not particularly limited unless otherwise specified in the specification.

[0018] Figure 1 schematically shows an example of the internal structure of the battery 100. Figure 1 may be an example of a cross-sectional view of the battery 100. In this embodiment, the details of the battery 100 will be explained using the case where the battery 100 is a coin-type non-aqueous secondary battery as an example.

[0019] [Overview of Battery 100] In this embodiment, the battery 100 stores electrical energy. The battery 100 also supplies the stored electrical energy to an external source. A power source can be created by connecting multiple batteries 100 in series and / or in parallel.

[0020] In this embodiment, the storage battery 100 is a lithium secondary battery. The storage battery 100 contains a non-aqueous electrolyte as the electrolyte. The storage battery 100 also contains, as the negative electrode active material, lithium metal (sometimes referred to as metallic lithium), an alloy of lithium metal and other metals, and at least one intermetallic compound of lithium metal and other metals (the term lithium metal, etc. may be used as a general term for these).

[0021] Because lithium metals have a very low potential and a very large theoretical capacity, using them as the negative electrode active material can yield excellent secondary batteries. In particular, using lithium metals as the negative electrode active material can yield extremely excellent secondary batteries.

[0022] However, if lithium metal is used as the negative electrode active material, dendrite-like lithium may be generated during charging and discharging. If dendrites grow, there is a possibility that a short circuit may occur in the battery. Also, if the organic solvent used as the electrolyte is reduced by lithium metal, for example, reduced decomposition products may accumulate on the negative electrode. If reduced decomposition products accumulate on the negative electrode, the internal resistance of the battery will increase.

[0023] According to one embodiment of the battery 100, the structure of the negative electrode of the battery 100 suppresses the generation and / or growth of dendrites. This stabilizes the negative electrode. According to another embodiment of the battery 100, the composition of the non-aqueous electrolyte stabilizes the negative electrode. According to yet another embodiment of the battery 100, the structure of the negative electrode of the battery 100 and the composition of the non-aqueous electrolyte stabilize the negative electrode.

[0024] [Structure of Battery 100] In this embodiment, the storage battery 100 comprises a positive electrode case 112, a negative electrode case 114, a spacer 116, and a metal spring 118. The storage battery 100 also comprises a positive electrode 120, a separator 130, a negative electrode 140, and a non-aqueous electrolyte 150. In this embodiment, the positive electrode 120 has a positive electrode current collector 122 and a positive electrode active material layer 124. In this embodiment, the negative electrode 140 has a negative electrode current collector 142, a negative electrode active material layer 144, and a coating layer 146.

[0025] In this embodiment, the positive electrode case 112 and the negative electrode case 114 are made of a conductive material having, for example, a disc-shaped thin plate form. In this embodiment, by assembling the positive electrode case 112 and the negative electrode case 114, a space is formed inside the positive electrode case 112 and the negative electrode case 114. Inside the space formed by the positive electrode case 112 and the negative electrode case 114, a metal spring 118, a positive electrode 120, a separator 130, a negative electrode 140, and a non-aqueous electrolyte 150 are housed. The positive electrode 120, the separator 130, and the negative electrode 140 are fixed inside the positive electrode case 112 and the negative electrode case 114 by the repulsive force of the metal spring 118.

[0026] In this embodiment, the spacer 116 holds, for example, a laminate of the positive electrode 120, separator 130, and negative electrode 140 inside the space formed by the positive electrode case 112 and the negative electrode case 114. The spacer 116 may also be used to position the laminate of the positive electrode 120, separator 130, and negative electrode 140. The spacer 116 may seal the gap formed between the positive electrode case 112 and the negative electrode case 114. The spacer 116 may contain an insulating material. In this embodiment, the spacer 116 insulates the positive electrode case 112 and the negative electrode case 114.

[0027] In Figure 1, for the purpose of facilitating drawing and explanation, a relatively large space is formed between the spacer 116 and the laminate of the positive electrode 120, separator 130, and negative electrode 140. However, a person skilled in the art who has read the description of this specification will understand that the size of the space between the spacer 116 and the laminate of the positive electrode 120, separator 130, and negative electrode 140 can be adjusted as appropriate. Alternatively, the spacer 116 may fix the laminate of the positive electrode 120, separator 130, and negative electrode 140 by making contact with it.

[0028] In this embodiment, the material of the metal spring 118 may be any conductive material, and its type is not particularly limited. The shape and size of the metal spring 118 are not particularly limited. The metal spring 118 may also be a washer.

[0029] [Positive electrode] In this embodiment, the positive electrode current collector 122 holds the positive electrode active material layer 124. The material of the positive electrode current collector 122 can be any chemically stable electron conductor in the storage battery 100, and its type is not particularly limited. Examples of materials for the positive electrode current collector 122 include aluminum, stainless steel, nickel, titanium, or alloys thereof. Examples of shapes for the positive electrode current collector 122 include foil, mesh, punched metal, expanded metal, etc. The thickness of the positive electrode current collector 122 is not particularly limited, but is preferably 5 to 200 μm. The thickness of the positive electrode current collector 122 may be 6 to 20 μm.

[0030] In this embodiment, the positive electrode active material layer 124 is formed on at least one surface of the positive electrode current collector 122. The thickness of the positive electrode active material layer 124 may be 1 to 300 μm or 2 to 200 μm per side of the positive electrode current collector 122. The positive electrode active material layer 124 includes, for example, a positive electrode active material and a binder (sometimes referred to as a binder). The positive electrode active material layer 124 may also include a conductive additive.

[0031] In one embodiment, the positive electrode active material layer 124 is formed by applying a paste containing the materials constituting the positive electrode active material layer 124 and an organic solvent to at least one surface of the positive electrode current collector 122, and then drying the paste. The type of organic solvent is not particularly limited, but examples of such organic solvents include N-methylpyrrolidone (NMP). In another embodiment, the positive electrode active material layer 124 is formed by mixing the materials constituting the positive electrode active material layer 124, molding them into a sheet, and then pressing the sheet-like mixture onto at least one surface of the positive electrode current collector 122.

[0032] The positive electrode active material can be any material that can insert and remove lithium ions and has a higher potential than the negative electrode active material, which is metallic lithium. For example, insertion-type transition metal oxides such as lithium layered oxide systems, olivine systems, and spinel systems are used. Examples of positive electrode active materials include (i) LiMnO2, LiNiO2, LiCoO2, and Li(Mn x Ni 1-x)O2, Li(Mn x Co 1-x )O2, Li(Ni y Co 1-y )O2, Li(Mn x Ni y Co 1-x-y )O2 and other layered oxides, (ii) Li2MnO3-LiNiO2, Li2MnO3-LiCoO2, Li2MnO3-Li(Ni y Co 1-y )O2 and other solid solutions, (iii) Li2MnSiO4, Li2NiSiO4, Li2CoSiO4, Li2(Mn x Ni 1-x )SiO4, Li2(Mn x Co 1-x )SiO4, Li2(Ni y Co 1-y )SiO4, Li2(Mn x Ni y Co 1-x-y )SiO4 and other silicates, (iv) LiMnBO3, LiNiBO3, LiCoBO3, Li(Mn x Ni 1-x )BO3, Li(Mn x Co 1-x )BO3, Li(Ni y Co 1-y )BO3, Li(Mn x Ni y Co 1-x-y )BO3 and other borates, (v) V2O5, (vi) LiV3O6, (vii) MnO and the like are exemplified. In the above formula, 0 < x < 1, 0 < y < 1, 0 < x + y < 1. These cathode active materials may be used alone or two or more cathode active materials may be combined.

[0033] As the cathode active material, a conversion-type high-capacity cathode active material may be used. Examples of the conversion-type high-capacity cathode active material include sulfur, sulfur compounds, iron fluoride, transition metal oxides, and the like. The conversion-type cathode active material does not contain lithium in the initial state. Therefore, by combining a cathode containing a conversion-type cathode active material and an anode containing lithium metal as the anode active material, the energy density of the non-aqueous electrolyte secondary battery is greatly improved.

[0034] In this embodiment, the binder binds the materials constituting the positive electrode active material layer 124 (e.g., positive electrode active material, conductive additive, etc.) and maintains the electrode shape of the positive electrode 120. The binder only needs to be chemically stable in the storage battery 100, and its type is not particularly limited. A thermoplastic resin or a thermosetting resin may be used as the binder. Examples of binders include polyethylene, polypropylene, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, and styrene-butadiene rubber.

[0035] In this embodiment, the conductive additive reduces the resistance of the positive electrode 120. The conductive additive is chemically stable in the battery 100 and has the desired electronic conductivity; its type is not particularly limited. Inorganic materials or organic materials may be used as the conductive additive. Examples of conductive additives include carbon materials. Examples of carbon materials include graphite, carbon black (e.g., acetylene black, Ketjenblack, etc.), coke, amorphous carbon, carbon fibers, carbon nanotubes, and graphene. These conductive additives may be used alone or in combination of two or more types.

[0036] [Separator] In this embodiment, the separator 130 separates the positive electrode 120 and the negative electrode 140. The separator 130 ensures ionic conductivity between the positive electrode 120 and the negative electrode 140, for example, by holding the electrolyte. Examples of materials for the separator 130 include polyethylene, polypropylene, ethylene-propylene copolymer, glass, or composites thereof. Examples of shapes for the separator 130 include microporous film, nonwoven fabric, and filter. The separator 130 may also be a laminate of these films or the like. The thickness of the separator 130 is not particularly limited, but is preferably 10 to 50 μm. The aperture ratio of the separator 130 is not particularly limited, but is preferably 30 to 70%.

[0037] [Negative electrode] In this embodiment, the negative electrode current collector 142 holds the negative electrode active material layer 144. The negative electrode current collector 142 is made of a material that does not react with lithium. Examples of materials for the negative electrode current collector 142 include copper, aluminum, stainless steel, nickel, titanium, or alloys thereof. The negative electrode current collector 142 may comprise a resin support layer and a metal layer disposed on the surface of the support layer. Examples of the resin include polyethylene, polypropylene, polyethylene terephthalate, and polyimide. The metal layer may be made of copper, aluminum, stainless steel, nickel, titanium, or alloys thereof. The metal layer may include a layer made of copper, aluminum, stainless steel, nickel, titanium, or alloys thereof. The metal layer may be a foil or a plated layer.

[0038] Examples of the shape of the negative electrode current collector 142 include foil, mesh, punched metal, and expanded metal. The thickness of the negative electrode current collector 142 is not particularly limited, but may be 5 to 200 μm. Preferably, the thickness of the negative electrode current collector 142 is 6 to 20 μm.

[0039] In this embodiment, the negative electrode active material layer 144 is formed on at least one surface of the negative electrode current collector 142. The negative electrode active material layer 144 may be formed on only one surface of the sheet-like, film-like, or foil-like negative electrode current collector 142, or it may be formed on both surfaces of the negative electrode current collector 142. The thickness of the negative electrode active material layer 144 may be 1 to 200 μm or 4 to 100 μm per side of the negative electrode current collector 142.

[0040] In this embodiment, the negative electrode active material layer 144 includes at least one of lithium metal (sometimes referred to as metallic lithium), an alloy of lithium metal and another metal, and an intermetallic compound of lithium metal and another metal as the negative electrode active material. The negative electrode active material layer 144 may be a layer made of the above-mentioned lithium, etc. The negative electrode active material layer 144 may contain lithium metal as the negative electrode active material. The negative electrode active material layer 144 may be a layer made of lithium metal.

[0041] The negative electrode active material layer 144 may be a lithium metal foil. The thickness of the lithium metal foil may be 1 to 200 μm, 2 to 100 μm, and preferably 4 to 50 μm. The thickness and / or mass of the lithium metal foil may be determined according to the content of the positive electrode active material in the positive electrode active material layer 124.

[0042] In one embodiment, the negative electrode active material layer 144 is formed by pressing a sheet-like, film-like, or foil-like material constituting the negative electrode active material layer 144 onto the surface of at least one side of the negative electrode current collector 142. In another embodiment, the negative electrode active material layer 144 is formed by depositing the material constituting the negative electrode active material layer 144 onto the surface of at least one side of the negative electrode current collector 142 by (i) physical vapor deposition (PVD) methods such as sputtering, vapor deposition, or ion plating, (ii) chemical vapor deposition (CVD), or (iii) atomic layer deposition (ALD).

[0043] In this embodiment, the coating layer 146 is disposed on at least one surface of the negative electrode active material layer 144. In one embodiment, the coating layer 146 is disposed on one of the two surfaces of the sheet-like, film-like, or foil-like negative electrode active material layer 144, on the surface opposite to the surface in contact with the negative electrode current collector 142. Of the two surfaces of the sheet-like, film-like, or foil-like negative electrode active material layer 144, the coating layer 146 does not have to be disposed on the surface in contact with the negative electrode current collector 142.

[0044] In this case, the coating layer 146 may be arranged to entirely cover the negative electrode active material layer 144 disposed in contact with the negative electrode current collector 142. For example, as shown in FIG. 1, the coating layer 146 is arranged such that a part of the coating layer 146 is in contact with the negative electrode current collector 142. The size of the coating layer 146 may be larger than the size of the negative electrode active material layer 144. Thereby, the coating layer 146 can entirely cover the negative electrode active material layer 144 disposed in contact with the negative electrode current collector 142.

[0045] In other embodiments, the coating layer 146 is disposed on both main surfaces of the sheet-like, film-like or foil-like negative electrode active material layer 144. In this case, the coating layer 146 is interposed between the negative electrode current collector 142 and the negative electrode active material layer 144. Thereby, the coating layer 146 can entirely cover the negative electrode active material layer 144 disposed on the negative electrode current collector 142.

[0046] In the present embodiment, the coating layer 146 has the general formula M x A y (M is one element selected from the group consisting of Al, In, Mg, Ag, Si, and Sn, A is one element selected from the group consisting of O, N, P, and F, and 0.3 < x / y < 3). The coating layer 146 is made of a compound represented by the above general formula M x A y By forming the coating layer 146 from a compound represented by, a coating layer 146 excellent in conductivity or ion conductivity can be obtained.

[0047] According to the present embodiment, by including Al, In, Mg, Ag, Si, or Sn in the coating layer 146, the generation and / or growth of Li dendrites is suppressed. Further, as will be described later, the non-aqueous electrolyte 150 may contain an organic compound having a fluorine atom as a liquid organic solvent. In this case, the above general formula M x A yThe interaction between Al, In, Mg, Ag, Si, or Sn contained in the compound represented by and the fluorine atoms contained in the organic compound used as the organic solvent in the non-aqueous electrolyte 150 more effectively suppresses the generation and / or growth of Li dendrites. The mechanism is not clear, but the general formula M x A y It is presumed that the interaction between the compound represented by and the organic compound containing a fluorine atom results in the formation of a coating that is effective in suppressing the generation and / or growth of Li dendrites.

[0048] The coating layer 146 preferably contains Al and / or In. That is, M in the general formula is preferably one element selected from the group consisting of Al and In. The inclusion of Al and / or In in the coating layer 146 effectively suppresses the generation and / or growth of dendritic lithium.

[0049] The coating layer 146 preferably contains an oxide or nitride. That is, A in the general formula is preferably one element selected from the group consisting of O and N. General formula M x A y When the compound represented by is an oxide, a coating layer 146 with excellent strength can be obtained. As a result, the thickness of the coating layer 146 can be reduced, so a coating layer 146 with excellent conductivity or ionic conductivity can be obtained. x A y When the compound represented is a nitride, a coating layer 146 with excellent lithium ion conductivity can be obtained.

[0050] The coating layer 146 preferably contains at least one of Al2O3, In2O3, AlN, and InN. The coating layer 146 is preferably a layer composed of Al2O3, In2O3, AlN, or InN. This results in a coating layer 146 with excellent conductivity or ionic conductivity that effectively suppresses the generation and / or growth of dendrite-like lithium.

[0051] In this embodiment, the coating layer 146 has a thickness of 100 nm or less. The thickness of the coating layer 146 may be less than 50 nm, 30 nm or less, 20 nm or less, or 10 nm or less. This provides a coating layer 146 with excellent conductivity or ionic conductivity.

[0052] The coating layer 146 is formed by depositing the material constituting the coating layer 146 onto the surface of at least one side of the negative electrode active material layer 144, for example, by (i) physical vapor deposition (PVD) methods such as sputtering, vapor deposition, or ion plating, (ii) chemical vapor deposition (CVD), or (iii) atomic layer deposition (ALD). The method for producing the coating layer 146 is not particularly limited, as long as a coating layer 146 having the thickness described above is formed.

[0053] If the electrical conductivity or ionic conductivity of the coating layer 146 is low, the coating layer 146 itself acts as a resistive layer, causing a large overvoltage during charging and discharging. As a result, the performance of the storage battery 100 deteriorates. According to this embodiment, the coating layer 146 has a specific composition and thickness, and the coating layer 146 has excellent electrical conductivity or ionic conductivity. As a result, the occurrence of a large overvoltage during charging and discharging of the storage battery 100 is prevented.

[0054] The coating layer 146 contains general formula M x A y The elements constituting the compound represented by the general formula M may react with lithium contained in the battery 100 during the charging and discharging process of the battery 100. As a result, the negative electrode 140 reacts with lithium and the general formula M x A y The coating layer 146 may contain reaction products with elements that make up the compound represented by the general formula M x A y The compound may contain reaction products with elements that constitute the compound represented by . The above reaction products may form a film. For example, the above reaction products form a film on the surface of the coating layer 146.

[0055] In one embodiment, during the charging and discharging process of the storage battery 100, lithium contained in the storage battery 100 and general formula M x A y An alloy can be formed with the elements constituting the compound represented by the formula M. The alloy may be a solid solution or an intermetallic compound. The above alloy is lithium and the element constituting the compound of the general formula M. x A y It may be an alloy of lithium and an element represented by M contained in a compound represented by the general formula M. In this case, for example, after the battery 100 has been charged and discharged at least once, the negative electrode 140 is lithium and the element represented by the general formula M x A y The coating layer 146 may contain an alloy of lithium and an element represented by the general formula M. x A y The compound may also contain an alloy with the element represented by M. The above alloy may form a coating.

[0056] In another embodiment, the general formula M of the coating layer 146 x A y If the compound represented by contains nitrogen as the element represented by A, lithium nitride may be produced during the charging and discharging process of the battery 100. In this case, for example, after the battery 100 has been charged and discharged at least once, the negative electrode 140 may contain lithium nitride. The coating layer 146 may also contain lithium nitride. The lithium nitride may form a film.

[0057] [Electrolyte] In this embodiment, the non-aqueous electrolyte 150 enables ionic conduction between the positive electrode active material and the negative electrode active material via the electrolyte contained in the non-aqueous electrolyte 150. A known organic electrolyte may be used as the non-aqueous electrolyte 150. The non-aqueous electrolyte 150 includes, for example, a lithium salt or sodium salt as the electrolyte and a polar solvent. The polar solvent may be an organic solvent.

[0058] The lithium salts listed above can be any type that dissociates in a solvent to form lithium ions and is unlikely to undergo side reactions such as decomposition within the voltage range used in batteries; their type is not particularly limited. Examples of lithium salts include (i) inorganic lithium salts such as LiClO4, LiPF6, LiBF4, LiAsF6, and LiSbF6, and (ii) LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiN(FSO2)2, LiN(CF3SO2)2, LiC(CF3SO2)3, and LiC n F 2n+1 SO3(n is an integer greater than or equal to 2), LiN(R f OSO2)2(R f is a substituted or unsubstituted fluoroalkyl group. Examples include organolithium salts such as ). LiN(FSO2)2 is sometimes referred to as LiFSI. LiN(CF3SO2)2 is sometimes referred to as LiTFSI.

[0059] The lithium salts mentioned above may be used individually or in combination of two or more. Preferably, one or more of the following lithium salts are used: lithium hexafluoride phosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), and LiBF4 (lithium borofluoride).

[0060] The above-mentioned organic solvents are not limited in type, as long as they dissolve the lithium salts mentioned above and are unlikely to cause side reactions such as decomposition within the voltage range used for batteries. Examples of organic solvents include: (i) cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; (ii) linear carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; (iii) linear esters such as methyl propionate; (iv) cyclic esters such as γ-butyrolactone; (v) linear ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme; (vi) cyclic ethers such as dioxane, tetrahydrofuran, and 2-methyltetrahydrofuran; (vii) nitriles such as acetonitrile, propionitrile, and methoxypropionitrile; and (viii) sulfite esters such as ethylene glycol sulfite.

[0061] The above organic solvents may be used alone or in combination with two or more lithium salts. Preferably, one or more carbonate compounds and ether compounds are used as the organic solvent. Examples of the above carbonate compounds include propylene carbonate, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and fluoroethylene methyl carbonate (FEMC). Examples of the above ether compounds include 1,2-dimethoxyethane (DME).

[0062] The carbonate compounds and / or ether compounds described above are more susceptible to reductive decomposition by the lithium metal of the negative electrode active material layer 144 compared to other organic solvents. In this embodiment, since the lithium metal of the negative electrode active material layer 144 of the negative electrode 140 is covered by the coating layer 146, even if the non-aqueous electrolyte 150 contains the carbonate compounds and ether compounds described above, the reductive decomposition of the non-aqueous electrolyte 150 by the lithium metal is suppressed.

[0063] The above organic solvent may contain an organic compound having a fluorine atom. Preferably, the above organic solvent contains a cyclic carbonate having a fluorine atom. Preferably, the above organic solvent contains one or more of the above-mentioned organic solvents and a cyclic carbonate having a fluorine atom. An example of a cyclic carbonate having a fluorine atom is fluorinated ethylene carbonate. Examples of fluorinated ethylene carbonates include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and fluoroethylene methyl carbonate (FEMC). Other examples of organic compounds having a fluorine atom include fluorinated ether and fluorinated glime. Preferably, the above organic solvent contains one or more of the above-mentioned organic solvents and a fluorinated ethylene carbonate.

[0064] The proportion of cyclic carbonate containing fluorine atoms to the total amount of organic solvent in the non-aqueous electrolyte 150 is preferably 20 mol% or more. The proportion of cyclic carbonate containing fluorine atoms to the total amount of organic solvent used in the non-aqueous electrolyte 150 may be 20 mol% or more and 80% or less, 25 mol% or more and 70 mol% or less, or 30 mol% or more and 60 mol% or less.

[0065] The proportion of cyclic carbonate containing fluorine atoms to the total non-aqueous electrolyte 150 may be 20 mol% or more. For example, the ratio of the number of moles of cyclic carbonate containing fluorine atoms to the total number of moles of electrolyte and organic solvent contained in the non-aqueous electrolyte 150 is 20 mol% or more. The above proportion may be 20 mol% or more and 80% or less, 25 mol% or more and 70 mol% or less, or 30 mol% or more and 60 mol% or less. If the non-aqueous electrolyte 150 contains cyclic carbonate containing multiple types of fluorine atoms, the ratio of the total number of moles of cyclic carbonate containing multiple types of fluorine atoms to the total number of moles of electrolyte and organic solvent used in the non-aqueous electrolyte 150 may be 20 mol% or more. The above proportion may be 20 mol% or more and 80% or less, 25 mol% or more and 70 mol% or less, or 30 mol% or more and 60 mol% or less.

[0066] The non-aqueous electrolyte 150 contains a cyclic carbonate having a fluorine atom as at least a portion of its main organic solvent, thereby suppressing the reductive decomposition of the carbonate and ether compounds contained in the organic solvent. In particular, ethylene fluoride carbonate contains a fluorine atom with high electronegativity. Therefore, the inclusion of ethylene fluoride carbonate in the organic solvent significantly suppresses the reductive decomposition of the carbonate and ether compounds contained in the organic solvent.

[0067] In one embodiment of the non-aqueous electrolyte 150, LiPF6 is used as the electrolyte, and a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is used as the polar solvent. A cyclic carbonate having a fluorine atom may be further added to the above mixed solvent. For example, fluorinated ethylene carbonate may be added to the above mixed solvent.

[0068] In other embodiments of the non-aqueous electrolyte 150, LiTFSI is used as the electrolyte, and a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is used as the polar solvent. A cyclic carbonate having a fluorine atom may be further added to the above mixed solvent. For example, fluorinated ethylene carbonate is added to the above mixed solvent.

[0069] In yet another embodiment of the non-aqueous electrolyte 150, LiBF4 is used as the electrolyte, and a mixed solvent of propylene carbonate (PC) and ethyl methyl carbonate (EMC) is used as the polar solvent. A cyclic carbonate having a fluorine atom may be added to the above mixed solvent. For example, ethylene fluoride carbonate may be added to the above mixed solvent.

[0070] The concentration of lithium salt in non-aqueous electrolyte 150 is not particularly limited, but may be in the range of 0.1 to 5.0 mol / L. The concentration of lithium salt may also be in the range of 0.5 to 4.0 mol / L, or in the range of 0.7 to 1.5 mol / L.

[0071] As described above, according to this embodiment, the negative electrode 140 comprises a negative electrode active material layer 144 containing lithium metal and a general formula M x A y The battery includes a laminate with a coating layer 146 made of a compound represented by [formula]. This suppresses the reduction of the non-aqueous electrolyte by lithium metal. It also suppresses the generation of dendrite-like lithium during charging and discharging of the lithium secondary battery. In particular, when the non-aqueous electrolyte 150 contains propylene carbonate, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluoroethylene methyl carbonate (FEMC), or 1,2-dimethoxyethane (DME), the effect of the negative electrode 140 including a laminate of the negative electrode active material layer 144 and the coating layer 146 becomes particularly pronounced.

[0072] (a) When the negative electrode 140 comprises a laminate of a negative electrode active material layer 144 and a coating layer 146, and (b) when the non-aqueous electrolyte 150 is a mixed solvent of (i) one or more compounds selected from the group consisting of propylene carbonate, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), fluoroethylene methyl carbonate (FEMC), and 1,2-dimethoxyethane (DME), and (ii) a cyclic carbonate having a fluorine atom, the reduction of the non-aqueous electrolyte by lithium metal is effectively suppressed. Furthermore, the generation of dendrite-like lithium during charging and discharging of the lithium secondary battery is effectively suppressed.

[0073] The storage battery 100 may be an example of a lithium secondary battery. The negative electrode active material layer 144 may be an example of a first layer. The coating layer 146 may be an example of a second layer. The laminate of the first and second layers may be an example of a negative electrode material.

[0074] [An example of an alternative embodiment] In this embodiment, the details of the storage battery 100 were described using the case where the storage battery 100 is a coin-type secondary battery as an example. However, the type and structure of the storage battery 100 are not limited to this embodiment. In other embodiments, the storage battery 100 may be a cylindrical battery comprising a wound electrode body in which a positive electrode, a separator, and a negative electrode are wound in a spiral shape. In yet another embodiment, the storage battery 100 may be a laminated battery in which a laminated electrode body, in which a positive electrode and a negative electrode are alternately stacked with a separator in between, is sealed with a laminate.

[0075] In this embodiment, the details of the storage battery 100 were described as an example in which the negative electrode 140 has a negative electrode current collector 142 and a negative electrode active material layer 144. However, the negative electrode of the storage battery 100 is not limited to this embodiment. In other embodiments, if, for example, lithium metal foil is used as the negative electrode active material layer 144, the storage battery 100 may not have a negative electrode current collector 142.

[0076] In this embodiment, an example of a storage battery 100 was described using a non-aqueous electrolyte 150 as the electrolyte for the storage battery 100. However, the electrolyte for the storage battery 100 is not limited to this embodiment. In other embodiments, a gel electrolyte may be used as the electrolyte for the storage battery 100. A gel electrolyte can be obtained, for example, by adding a known gelling agent to the non-aqueous electrolyte 150 described above. In yet another embodiment, a known ionic liquid may be used as the electrolyte for the storage battery 100.

[0077] [Manufacturing method for storage battery 100] Figure 2 schematically shows an example of a method for manufacturing a storage battery 100. According to this embodiment, first, in step 212 (the step may be abbreviated as S), for example, a sheet-shaped negative electrode current collector 142 and a lithium metal foil as a negative electrode active material layer 144 are prepared. Next, in S214, the negative electrode current collector 142 and the lithium metal foil are laminated. For example, the lithium metal foil is pressed onto the surface of at least one side of the negative electrode current collector 142.

[0078] Next, in S216, a coating layer 146 having a thickness of 100 nm or less is laminated on at least a portion of the surface of the lithium metal foil pressed onto the negative electrode current collector 142, on the side opposite to the surface in contact with the negative electrode current collector 142. The coating layer 146 is formed, for example, by physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD). At this time, the coating layer 146 is formed so that it completely covers the surface of the lithium metal foil.

[0079] Next, in S218, the battery 100 is assembled. Specifically, first, the positive electrode 120, separator 130, negative electrode 140, spacer 116, and metal spring 118 are placed inside the positive electrode case 112 and the negative electrode case 114. Also, a non-aqueous electrolyte 150 is injected inside the positive electrode case 112 and the negative electrode case 114. After that, the positive electrode case 112 and the negative electrode case 114 are sealed, and the battery 100 is obtained.

[0080] [An example of an alternative embodiment] In this embodiment, a coating layer 146 is formed on the surface of the lithium metal foil after it has been pressed onto the negative electrode current collector 142. However, the procedure for manufacturing the negative electrode 140 is not limited to this embodiment. According to another embodiment, a coating layer 146 is formed on the surface of at least one side of the lithium metal foil, and then the lithium metal foil with the coating layer 146 is pressed onto the negative electrode current collector 142. [Examples]

[0081] For the purpose of providing a more detailed description of the battery 100, the details of the battery 100 will be explained by the following embodiment. In the following embodiment, the performance of the negative electrode is evaluated using a "symmetric cell". In a symmetric cell, two equivalent electrodes of equal material, mass, and thickness are arranged symmetrically within the cell. However, various modifications or improvements may be made to the following embodiment, and the battery 100 is not limited to the embodiment described below.

[0082] [Example 1] First, the negative electrode was fabricated using the following procedure. A 10 μm thick Cu foil was prepared as the negative electrode current collector 142. A 20 μm thick lithium metal foil was prepared as the negative electrode active material layer 144. Next, the lithium metal foil was pressed onto the surface of one side of the Cu foil. Subsequently, Al2O3 was deposited on the surface of the lithium metal foil by PVD to form an Al2O3 layer as the coating layer 146. The thickness of the Al2O3 layer was 10 nm. This resulted in a negative electrode in which the Cu current collector, Li layer, and Al2O3 layer were stacked in this order.

[0083] Next, the positive electrode was fabricated using the same procedure as for the negative electrode. This resulted in a positive electrode in which a Cu current collector, a Li layer, and an Al2O3 layer were stacked in that order.

[0084] Furthermore, polyethylene with a thickness of 16 μm was prepared as separator 130. In addition, a non-aqueous electrolyte containing a mixed solvent of ethyl methyl carbonate and ethylene fluoride carbonate, and lithium hexafluoride phosphate was prepared. The ratio of lithium hexafluoride phosphate:ethylene fluoride carbonate:ethyl methyl carbonate was 12.6:18.0:69.4 (vol). The molar percentage of ethylene fluoride carbonate relative to the total mixed solvent was 20 mol% or more. A coin-type battery was fabricated using the positive electrode, negative electrode, separator, and non-aqueous electrolyte described above. This resulted in the creation of a symmetrical cell for evaluation.

[0085] [Example 2] A coin-type battery was fabricated using the same procedure as in Example 1, except that the mixing ratio of lithium hexafluoride phosphate, ethylene fluoride carbonate, and ethyl methyl carbonate in the non-aqueous electrolyte was 12.8:22.1:65.1 (vol %). This resulted in the creation of a symmetrical cell for evaluation.

[0086] [Comparative Example 1] First, the negative electrode was fabricated using the following procedure. A 10 μm thick copper foil was prepared as the negative electrode current collector 142. A 20 μm thick lithium metal foil was prepared as the negative electrode active material layer 144. This resulted in a negative electrode in which the copper current collector and the Li layer were stacked in this order.

[0087] Next, the positive electrode was fabricated using the same procedure as for the negative electrode. This resulted in a positive electrode in which the Cu current collector and Li layer were stacked in that order. A separator and non-electrolyte solution similar to those in Example 1 were also prepared. A coin-type battery was fabricated in the same manner as in Example 1. This resulted in the creation of a symmetrical cell for evaluation.

[0088] [Test Example 1] The cycle characteristics of the symmetrical cell fabricated in Example 1 were evaluated. Specifically, charging and discharging at a constant current were repeated 250 times, and the voltage values ​​during charging and discharging were recorded. The charging time per cycle was 1 hour, and the discharging time per cycle was 1 hour. The charging conditions were a temperature of 23°C and a current density of 1 mA / cm². 2 The current value was 0.2 [mA]. ​​The discharge conditions were a temperature of 23 [°C] and a current density of 1 [mA / cm²]. 2 The result was 0.2[mA].

[0089] The results of Test Example 1 are shown in Figure 3. In Example 1, two equivalent electrodes with the same material, mass, and thickness are used as the positive and negative electrodes. Therefore, the operating voltage is 0V, and the charge-discharge curve has a nearly symmetrical shape within the normal range of the electrodes. In Test Example 1, it can be seen that overvoltage is suppressed and the negative electrode is stable even after 500 hours have elapsed.

[0090] [Test Example 2] The cycle characteristics of the symmetrical cell prepared in Comparative Example 1 were evaluated. Specifically, charging and discharging at a constant current were repeated 250 times, and the voltage values ​​during charging and discharging were recorded. The charging time per cycle was 1 hour, and the discharging time per cycle was 1 hour. The charging and discharging conditions were the same as in Test Example 1.

[0091] The results of Test Example 2 are shown in Figure 4. In Test Example 2, it can be seen that overvoltage occurred after 500 hours.

[0092] [Test Example 3] The cycle characteristics of the symmetrical cell prepared in Example 2 were evaluated. Specifically, charging and discharging at a constant current were repeated 50 times, and the voltage values ​​during charging and discharging were recorded. The charging time per cycle was 1 hour, and the discharging time per cycle was 1 hour. The charging and discharging conditions were the same as in Test Example 1.

[0093] The results of the cycle characteristic test are shown in Figure 5. In Test Example 3, it can be seen that the overvoltage was suppressed and the negative electrode remained stable even after 100 hours had elapsed.

[0094] As described above, the anode was stabilized by forming a 10 nm Al2O3 layer on the surface of the lithium metal layer. As mentioned above, In, Mg, Ag, Si, and Sn can also suppress the generation and / or growth of dendritic lithium, similar to Al. Furthermore, oxides, nitrides, fluorides, and phosphides of these metals can form coating layers with excellent conductivity or ionic conductivity, similar to the Al2O3 layer. Therefore, according to this disclosure, the anode can be formed using the general formula M x A y It has been demonstrated that by incorporating a layer made of the compound represented by [the compound], the degradation of lithium secondary battery performance is suppressed and the stability during battery operation is improved.

[0095] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0096] It should be noted that the execution order of operations, procedures, steps, and stages in the apparatus, systems, programs, and methods described in the claims, specifications, and drawings is not explicitly stated as "before" or "prior to," and that these can be implemented in any order unless the output of a previous process is used in a later process. Even if the operation flow in the claims, specifications, and drawings is described using phrases such as "first," and "next," for convenience, this does not mean that it is essential to perform the operations in that order. [Explanation of Symbols]

[0097] 100 Battery, 112 Positive electrode case, 114 Negative electrode case, 116 Spacer, 118 Metal spring, 120 Positive electrode, 122 Positive electrode current collector, 124 Positive electrode active material layer, 130 Separator, 140 Negative electrode, 142 Negative electrode current collector, 144 Negative electrode active material layer, 146 Coating layer, 150 Non-aqueous electrolyte

Claims

1. The negative electrode of a lithium secondary battery containing a non-aqueous electrolyte, materials for the negative electrode, A negative electrode current collector holding the aforementioned negative electrode material, Equipped with, The aforementioned negative electrode material is, A first layer containing lithium metal as the negative electrode active material, A second layer disposed on at least one surface of the first layer, Equipped with, The aforementioned second layer is In ２ O ３ Alternatively, it consists of InN and has a thickness of 100 nm or less. The negative electrode is formed by stacking the negative electrode current collector, the first layer, and the second layer in this order.

2. The second layer has a thickness of 10 nm or less. The negative electrode according to claim 1.

3. The second layer is arranged to completely cover the first layer which is in contact with the negative electrode current collector. The negative electrode according to claim 1 or claim 2.

4. The second layer is arranged such that a portion of the second layer is in contact with the negative electrode current collector. The negative electrode according to any one of claims 1 to 3.

5. A negative electrode according to any one of claims 1 to 4, Positive electrode and, Non-aqueous electrolyte, A lithium-ion secondary battery equipped with these features.

6. The non-aqueous electrolyte contains a cyclic carbonate having a fluorine atom. The lithium secondary battery according to claim 5.

7. The proportion of the cyclic carbonate containing the fluorine atom to the total amount of the non-aqueous electrolyte is 20 mol% or more and 80 mol% or less. The lithium secondary battery according to claim 6.

8. The cyclic carbonate having a fluorine atom includes fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC). A lithium secondary battery according to either claim 6 or claim 7.

9. A method for manufacturing a negative electrode used in a lithium secondary battery containing a non-aqueous electrolyte, The first step involves preparing a layer containing lithium metal as the negative electrode active material, The steps include forming a second layer on at least one surface of the first layer, The steps include supporting the negative electrode material having the first layer and the second layer on a negative electrode current collector, It has, The aforementioned second layer is In ２ O ３ Alternatively, it consists of InN and has a thickness of 100 nm or less. A method in which the negative electrode current collector, the first layer, and the second layer are stacked in this order.

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