Anode, method for producing same, and battery

Abstract

This negative electrode is provided with an active material layer; and an inorganic solid electrolyte layer provided over the active material layer. The active material layer comprises, in the stated order from the side farther from the inorganic solid electrolyte layer, the following: a lithium metal layer; an interlayer containing lithium and oxygen as constituent elements; and a surface layer containing lithium, oxygen and carbon as constituent elements. The inorganic solid electrolyte layer contains a characteristic element other than lithium, oxygen, or carbon as a constituent element. In elemental analysis, using X-ray photoelectron spectroscopy, of the active material layer and the inorganic solid electrolyte layer in the depth direction, the ratio of the abundance of lithium to the abundance of carbon is greater than 2 at any depth within the range from a first intersection where the spectrum derived from the characteristic element and the spectrum derived from carbon intersect one another to a second intersection where the spectrum derived from lithium and the spectrum derived from oxygen intersect one another.

Description

[Technical Field]

[0001] The present technology relates to a negative electrode, a method for producing the same, and a battery. [Background technology]

[0002] Electrochemical devices such as batteries have become widespread, and their development is progressing. These electrochemical devices include a positive electrode and a negative electrode, and various studies have been conducted on the configuration of the negative electrode.

[0003] Specifically, in the process of forming the negative electrode, the surface of a lithium metal foil is treated with an acid solution, and then a solid electrolyte film is formed on the surface of the lithium metal foil (see, for example, Patent Document 1). Also, in the process of forming the negative electrode, the surface of a lithium metal foil is etched, and then a solid electrolyte film is formed on the surface of the lithium metal foil (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2005 / 186469 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-329524 Summary of the Invention

[0005] Although various studies have been conducted on the structure of the negative electrode, the electrical properties of the negative electrode are still insufficient and there is room for improvement.

[0006] There is a demand for a negative electrode capable of obtaining excellent electrical properties, a method for producing the same, and a battery.

[0007] According to one embodiment of the present technology, a negative electrode includes an active material layer and an inorganic solid electrolyte layer disposed on the active material layer. The active material layer includes, in order from the side farthest from the inorganic solid electrolyte layer, a lithium metal layer, an intermediate layer containing lithium and oxygen as constituent elements, and a surface layer containing lithium, oxygen, and carbon as constituent elements. The inorganic solid electrolyte layer includes a characteristic element other than lithium, oxygen, and carbon as a constituent element. In elemental analysis of the active material layer and the inorganic solid electrolyte layer in the depth direction using X-ray photoelectron spectroscopy, the ratio of the amount of lithium to the amount of carbon is greater than 2 at any depth within a range from a first intersection point where the spectrum derived from the characteristic element and the spectrum derived from carbon intersect with each other to a second intersection point where the spectrum derived from lithium and the spectrum derived from oxygen intersect with each other.

[0008] A method for manufacturing a negative electrode according to one embodiment of the present technology includes preparing a precursor in which a lithium metal layer, an intermediate layer containing lithium and oxygen as constituent elements, and a surface layer containing lithium, oxygen, and carbon as constituent elements are laminated in this order; rolling the precursor in a reduced pressure environment or an inert gas atmosphere to form an active material layer including the lithium metal layer, the intermediate layer, and the surface layer; and forming an inorganic solid electrolyte layer on the surface layer of the active material layer in a reduced pressure environment or an inert gas atmosphere.

[0009] A battery according to an embodiment of the present technology includes a positive electrode and a negative electrode, and the negative electrode has a configuration similar to that of the negative electrode according to the embodiment of the present technology described above.

[0010] According to one embodiment of the present technology, the negative electrode includes an active material layer (lithium metal layer, intermediate layer, and surface layer) and an inorganic solid electrolyte layer, the intermediate layer containing lithium and oxygen as constituent elements, the surface layer containing lithium, oxygen, and carbon as constituent elements, and the inorganic solid electrolyte layer containing a characteristic element different from lithium, oxygen, and carbon as a constituent element. Furthermore, elemental analysis of the active material layer and the inorganic solid electrolyte layer in the depth direction using X-ray photoelectron spectroscopy showed that the ratio of the amount of lithium to the amount of carbon present was greater than 2 at any depth within the range from the first intersection to the second intersection. Therefore, excellent electrical properties can be obtained.

[0011] According to a method for manufacturing a negative electrode of an embodiment of the present disclosure, a precursor including a lithium metal layer, an intermediate layer containing lithium and oxygen as constituent elements, and a surface layer containing lithium, carbon, and oxygen as constituent elements is prepared, and the precursor is rolled in a reduced pressure environment or an inert gas atmosphere to form an active material layer including the lithium metal layer, the intermediate layer, and the surface layer, and an inorganic solid electrolyte layer is formed on the surface layer of the active material layer in a reduced pressure environment or an inert gas atmosphere. Thus, a negative electrode having excellent electrical properties can be obtained.

[0012] Furthermore, according to the battery of one embodiment of the present technology, the battery includes a positive electrode and a negative electrode, and the negative electrode has the above-described configuration, thereby achieving excellent electrical characteristics.

[0013] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view illustrating a configuration of a negative electrode according to an embodiment of the present technology. [Figure 2] FIG. 2 is a diagram schematically showing the results of elemental analysis of the negative electrode (Example 1) in the depth direction using X-ray photoelectron spectroscopy. [Figure 3] 1A to 1C are cross-sectional views illustrating a method for manufacturing a negative electrode according to an embodiment of the present technology. [Figure 4] FIG. 4 is a cross-sectional view illustrating the method for manufacturing the negative electrode following FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view illustrating the method for manufacturing the negative electrode following FIG. 4. [Figure 6] FIG. 4 is an enlarged cross-sectional view showing a partial configuration of the precursor shown in FIG. [Figure 7] FIG. 5 is an enlarged cross-sectional view showing a partial configuration of the precursor shown in FIG. 4. [Figure 8] 1 is a cross-sectional view illustrating a configuration of a battery according to an embodiment of the present technology. [Figure 9] FIG. 2 is a diagram schematically showing the results of elemental analysis of the negative electrode (Comparative Example 1) in the depth direction using X-ray photoelectron spectroscopy. [Figure 10] FIG. 10 is a cross-sectional view illustrating a method for measuring interface resistance. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order. 1.Negative electrode 1-1. Overall structure 1-2.Detailed composition and physical properties 1-3.Operation 1-4. Manufacturing method 1-5. Action and effects 2.Battery 2-1.Configuration 2-2.Operation 2-3. Action and effects 3. Battery uses

[0016] <1. Negative electrode> First, the negative electrode according to an embodiment of the present technology will be described.

[0017] The negative electrode is used in electrochemical devices that utilize electrochemical reactions to perform various functions. The type of electrochemical device is not particularly limited, but specific examples include batteries and capacitors. The battery may be a primary battery or a secondary battery.

[0018] As will be described later, the negative electrode contains lithium metal, and thus, during the electrode reaction, the negative electrode releases lithium in an ionic state and absorbs the lithium in an ionic state.

[0019] <1-1. Overall structure> Figure 1 shows the cross-sectional structure of the negative electrode, although only a portion of the negative electrode is shown.

[0020] As shown in Fig. 1, this negative electrode includes an active material layer 1 and an inorganic solid electrolyte layer 2. The depth direction P shown in Fig. 1 is the direction from the inorganic solid electrolyte layer 2 toward the active material layer 1 (the direction toward the bottom in Fig. 1).

[0021] In the following description, for convenience, the upper side in FIG. 1 is referred to as the upper side of the negative electrode, and the lower side in FIG. 1 is referred to as the lower side of the negative electrode.

[0022] [Active material layer] The active material layer 1 is a layer that absorbs and releases lithium in an ionic state during an electrode reaction, and contains lithium metal. Specifically, the active material layer 1 includes, in order from the side farthest from the inorganic solid electrolyte layer 2, a lithium metal layer 1X, an intermediate layer 1Y, and a surface layer 1Z. That is, the active material layer 1 has a structure in which the lithium metal layer 1X, the intermediate layer 1Y, and the surface layer 1Z are laminated in this order.

[0023] (lithium metal layer) The lithium metal layer 1X is a lithium supply source, and specifically, is a lithium metal foil or the like.

[0024] However, the purity of the lithium metal layer 1X, i.e., the purity of the lithium metal, is not necessarily limited to 100%. Therefore, the lithium metal layer 1X may contain a trace amount of impurities within a practical range due to factors such as the manufacturing method of the lithium metal foil.

[0025] The thickness T1 of the lithium metal layer 1X is not particularly limited as long as it is within a range that ensures the amount of lithium released and absorbed. The procedure for determining the thickness T1 will be described later.

[0026] Specifically, the thickness T1 is preferably 10 μm or more, and more preferably 10 μm to 1000 μm, because the thickness T1 is sufficiently large, allowing the lithium metal layer 1X to release and store a sufficient amount of lithium in an ionic state during the electrode reaction.

[0027] In detail, as will be described later, in the process of producing the negative electrode, the precursor 3 is rolled to form the active material layer 1 including the lithium metal layer 1X, the intermediate layer 1Y, and the surface layer 1Z, and then the inorganic solid electrolyte layer 2 is formed on the surface layer 1Z of the active material layer 1. In contrast, in the process of producing the negative electrode, it is conceivable to form the lithium metal layer 1X by depositing lithium metal on the inorganic solid electrolyte layer 2 using a vapor phase film formation method such as vacuum deposition.

[0028] However, when the lithium metal layer 1X is formed using a vapor phase deposition method, it is difficult to form the lithium metal layer 1X so that the thickness T1 is sufficiently large due to the film formation principle of the vapor phase deposition method. Specifically, the thickness T1 when the vapor phase deposition method is used is at most several tens of nanometers. As a result, due to the small thickness T1, it is difficult for the lithium metal layer 1X to release and absorb a sufficient amount of lithium in an ionic state during the electrode reaction.

[0029] In contrast, when the active material layer 1 is formed by rolling the precursor 3, the thickness T1 is determined depending on conditions such as the progress and number of times of the rolling, and therefore it is possible to form the lithium metal layer 1X so that the thickness T1 is sufficiently large to a degree that would be impossible to achieve using a vapor phase film formation method. Specifically, when the rolling process of the precursor 3 is used, the thickness T1 is 10 μm or more, as described above. This sufficiently large thickness T1 enables the lithium metal layer 1X to release and absorb a sufficient amount of lithium in the ionic state during the electrode reaction.

[0030] (middle class) The intermediate layer 1Y is a layer formed by modifying a portion of the surface vicinity of the lithium metal layer 1X. More specifically, the intermediate layer 1Y is formed by the reaction of lithium with oxygen and water in the environment near the surface of the lithium metal layer 1X. As a result, the intermediate layer 1Y contains lithium and oxygen as constituent elements. Specifically, the intermediate layer 1Y contains lithium oxide (LiO).

[0031] (Surface layer) The surface layer 1Z is the outermost layer of the active material layer 1 and is adjacent to the inorganic solid electrolyte layer 2. That is, the surface layer 1Z is interposed between the intermediate layer 1Y and the inorganic solid electrolyte layer 2, and has a thickness T2. The procedure for determining the thickness T2 will be described later.

[0032] This surface layer 1Z is another layer formed by modifying a portion of the surface vicinity of the lithium metal layer 1X, and more specifically, is formed as a result of lithium reacting with oxygen, carbon dioxide, water, etc. in the environment near the surface of the lithium metal layer 1X. As a result, the surface layer 1Z contains lithium, oxygen, and carbon as constituent elements.

[0033] Specifically, the surface layer 1Z contains lithium carbonate (Li2CO3) and lithium hydroxide (LiOH), etc. However, the surface layer 1Z may further contain any organic substance.

[0034] Materials such as lithium carbonate contained in surface layer 1Z act as unnecessary components with high electrical resistance (hereinafter referred to as "high resistance components"), and increase the electrical resistance (hereinafter referred to as "interface resistance R") at the interface between active material layer 1 and inorganic solid electrolyte layer 2. In this case, when thickness T2 increases, the amount of surface layer 1Z formed increases, and therefore, interface resistance R is more likely to increase.

[0035] 1 shows a case where the intermediate layer 1Y and the surface layer 1Z are provided on only one surface (top surface) of the lithium metal layer 1X for the sake of simplicity, but the intermediate layer 1Y and the surface layer 1Z may be provided on both surfaces (top and bottom surfaces) of the lithium metal layer 1X.

[0036] As described above, the manufacturing process of the negative electrode involves rolling the precursor 3, and therefore the negative electrode has an appropriate structure and physical properties that can reduce the interfacial resistance R. The detailed structure and physical properties of the negative electrode will be described later.

[0037] [Inorganic solid electrolyte layer] Since the inorganic solid electrolyte layer 2 is provided on the active material layer 1, the surface (surface layer 1Z) of the active material layer 1 is covered with the inorganic solid electrolyte layer 2. As a result, the inorganic solid electrolyte layer 2 functions as a protective film that protects the surface of the active material layer 1.

[0038] Specifically, the inorganic solid electrolyte layer 2 protects the surface of the active material layer 1 from oxygen, carbon dioxide, water, and the like present in the environment. As a result, the inorganic solid electrolyte layer 2 suppresses the formation of a new high-resistance component (surface layer 1Z) on the outermost surface of the active material layer 1, more specifically, between the intermediate layer 1Y and the inorganic solid electrolyte layer 2.

[0039] Furthermore, when lithium is released and absorbed in an ionic state in the negative electrode, the inorganic solid electrolyte layer 2 prevents the lithium from being deposited in a metallic state on the surface of the active material layer 1. This prevents the growth of lithium dendrites on the surface of the active material layer 1, thereby preventing the occurrence of short circuits caused by the lithium dendrites in electrochemical devices in which the negative electrode is used together with a positive electrode. This improves the safety and lifespan of the electrochemical device.

[0040] When the inorganic solid electrolyte layer 2 contains lithium as a constituent element, the inorganic solid electrolyte layer 2 may function as a lithium supply source, similar to the lithium metal layer 1X.

[0041] Here, as described above, the intermediate layer 1Y and the surface layer 1Z are provided on only one surface of the lithium metal layer 1X, and therefore the inorganic solid electrolyte layer 2 is provided on only one surface (upper surface) of the active material layer 1. However, when the intermediate layer 1Y and the surface layer 1Z are provided on both surfaces of the lithium metal layer 1X, the inorganic solid electrolyte layer 2 may be provided on both surfaces (upper and lower surfaces) of the active material layer 1.

[0042] This inorganic solid electrolyte layer 2 contains a characteristic element as a constituent element, more specifically, it contains one or more types of inorganic solid electrolyte materials. This characteristic element is one or more types of elements other than lithium, carbon, and oxygen. That is, the inorganic solid electrolyte layer 2 contains an element (characteristic element) that is not contained in the active material layer 1 (lithium metal layer 1X, intermediate layer 1Y, and surface layer 1Z), and the type of the characteristic element may be only one type or two or more types. The crystalline state of the inorganic solid electrolyte material is not particularly limited, and may be crystalline, amorphous (amorphous), or may contain both crystalline and amorphous.

[0043] The type of inorganic solid electrolyte material is not particularly limited and can be selected arbitrarily. Specific examples of inorganic solid electrolyte materials include amorphous LiPO (LPO), LiPON, and LiLaZrO. 12(LLZO), LiSiCON, Li 1.4 Ti2Si 0.4 P 2.6 O 12 -AlPO4(LATP), alumina, Li3PS4(LPS), Li 10 GeP2S 12 Examples of inorganic solid electrolyte materials include LPO, LLZO, LATP, LPS, LGPS, and argyrodite (Li6PS5Cl), and polyethylene oxide (PEO). However, the compositions of LPO, LLZO, LATP, LPS, LGPS, and argyrodite are not limited to the above compositions and can be changed as desired. Characteristic elements of the inorganic solid electrolyte materials exemplified here include phosphorus, zirconium, silicon, titanium, aluminum, sulfur, and germanium.

[0044] Among these, the inorganic solid electrolyte material contains lithium, oxygen, and phosphorus as a characteristic element as constituent elements, and the lithium content in the inorganic solid electrolyte material is preferably 10 atomic % to 60 atomic %. This is because the inorganic solid electrolyte layer 2 can function satisfactorily as a protective film and can also function satisfactorily as a lithium supply source.

[0045] Therefore, it is preferable that the inorganic solid electrolyte material contains one or more of amorphous Li3PO4, LiPON, and the like.

[0046] The thickness T3 of the inorganic solid electrolyte layer 2 is not limited as long as the inorganic solid electrolyte layer 2 can function as a protective film and a lithium supply source. In particular, the thickness T3 is preferably 10 nm to 20,000 nm. This is because the inorganic solid electrolyte layer 2 can function satisfactorily as a protective film and can also function satisfactorily as a lithium supply source. The procedure for determining the thickness T3 will be described later.

[0047] <1-2. Detailed composition and physical properties> Fig. 2 shows a schematic representation of the results of elemental analysis (photoelectron spectrum) of the negative electrode (active material layer 1 and inorganic solid electrolyte layer 2) in the depth direction P using X-ray photoelectron spectroscopy (XPS). In Fig. 2, the horizontal axis represents the depth D (nm) and the vertical axis represents the abundance M (atomic %).

[0048] Here, the inorganic solid electrolyte layer 2 contains lithium, oxygen, and a characteristic element (phosphorus) as constituent elements, more specifically, the inorganic solid electrolyte layer 2 contains amorphous Li3PO4. As a result, Figure 2 shows a lithium (Li1s) spectrum S1 (thick solid line) that is a spectrum derived from lithium, an oxygen (O1s) spectrum S2 (thick dashed line) that is a spectrum derived from oxygen, a carbon (C1s) spectrum S3 (thin solid line) that is a spectrum derived from carbon, and a phosphorus (P2p) spectrum S4 (thin dashed line) that is a spectrum derived from the characteristic element (phosphorus).

[0049] [Elemental analysis using XPS] By performing elemental analysis of the negative electrode in the depth direction P using XPS, the photoelectron spectrum shown in Fig. 2 is obtained. As is clear from Fig. 2, this depth direction P is the direction in which the depth D increases.

[0050] In this elemental analysis of the anode, the amount of each element (lithium, oxygen, carbon, and phosphorus) is measured while etching the surface of the anode by alternately repeating an etching process using ion sputtering and measuring the amount of each element (lithium, oxygen, carbon, and phosphorus). As a result, Figure 2 shows the relationship between the depth D (horizontal axis), which is the so-called sputtering depth, and the amount M (vertical axis) of each element.

[0051] As described above, the negative electrode includes an active material layer 1 and an inorganic solid electrolyte layer 2 (amorphous LiPO), and the active material layer 1 includes a lithium metal layer 1X (lithium metal), an intermediate layer 1Y (lithium oxide, etc.), and a surface layer 1Z (lithium carbonate, etc.). That is, in the negative electrode, the inorganic solid electrolyte layer 2 / surface layer 1Z / intermediate layer 1Y / lithium metal layer 1X are arranged in this order in the depth direction P.

[0052] As a result, the abundance M of each element (lithium, oxygen, carbon, and phosphorus) changes as explained below. Hereinafter, the abundance M of lithium is defined as ML, the abundance M of oxygen as MO, the abundance M of carbon as MC, and the abundance M of phosphorus as MP.

[0053] As is clear from the behavior of the lithium spectrum S1, the abundance ML increases rapidly from an almost constant state, and then becomes almost constant.

[0054] As is clear from the behavior of the oxygen spectrum S2, the abundance MO starts out nearly constant, then decreases rapidly, and then becomes nearly constant.

[0055] As is clear from the behavior of carbon spectrum S3, the abundance MC temporarily increases from approximately 0 atomic % and then decreases to approximately 0 atomic % again.

[0056] As is clear from the behavior of the phosphorus spectrum S4, the abundance MP decreases rapidly from a nearly constant state to nearly 0 atomic %.

[0057] Here, attention is focused on the point where the phosphorus spectrum S4 and the carbon spectrum S3 intersect with each other (point A, which is the first intersection point), the point where the lithium spectrum S1 and the oxygen spectrum S2 intersect with each other (point B, which is the second intersection point), the point where the abundance ML in the lithium spectrum S1 finally begins to become approximately constant (point C), and the point where the abundance MO in the oxygen spectrum S2 finally begins to become approximately constant (point D). Note that "the abundance ML becomes approximately constant" means that the amount of variation in the abundance ML is within ±2.5 atomic %, and "the abundance MO becomes approximately constant" means that the amount of variation in the abundance MO is within ±2.5 atomic %.

[0058] In this case, point A corresponds to the boundary between the inorganic solid electrolyte layer 2 and the active material layer 1, i.e., the position of the interface between the inorganic solid electrolyte layer 2 and the surface layer 1Z. Point B corresponds to the position of the boundary (interface) between the surface layer 1Z and the intermediate layer 1Y. Points C and D each correspond to the position of the boundary (interface) between the intermediate layer 1Y and the lithium metal layer 1X.

[0059] The depth D corresponding to point A is designated as D1, the depth D corresponding to point B as D2, and the depth D corresponding to points C and D as D3. Thus, the range (region α) where depth D = 0 to D1 corresponds to the region where the inorganic solid electrolyte layer 2 exists. The range (region β) where depth D = D1 to D2 corresponds to the region where the surface layer 1Z exists. The range (region γ) where depth D = D2 to D3 corresponds to the region where the intermediate layer 1Y exists. The range (region δ) beyond depth D = D3 corresponds to the region where the lithium metal layer 1X exists. In FIG. 2, region β, which is the region where the surface layer 1Z exists, is shaded.

[0060] That is, the depth D1 corresponds to the thickness T3 of the inorganic solid electrolyte layer 2, and the depth D2-D1 corresponds to the thickness T2 of the surface layer 1Z.

[0061] Therefore, the abundance ML increases rapidly near the depth D = D1, and then becomes substantially constant at the depth D = D3. This is because, although the inorganic solid electrolyte layer 2, the surface layer 1Z, the intermediate layer 1Y, and the lithium metal layer 1X all contain lithium as a constituent element, the lithium content is greater in the lithium metal layer 1X than in the inorganic solid electrolyte layer 2.

[0062] The abundance of MO decreases rapidly near the depth D = D1 and then becomes substantially constant at the depth D = D3. This is because the inorganic solid electrolyte layer 2, the intermediate layer 1Y, and the surface layer 1Z each contain oxygen as a constituent element, whereas the lithium metal layer 1X contains almost no oxygen as a constituent element.

[0063] The abundance MC is initially approximately 0 atomic %, but temporarily increases near depth D = D1, and then decreases near depth D = D2, thereby becoming approximately 0 atomic % again. This is because the surface layer 1Z contains carbon as a constituent element, but the inorganic solid electrolyte layer 2, the intermediate layer 1Y, and the lithium metal layer 1X each contain almost no carbon as a constituent element.

[0064] The abundance MP rapidly decreases to approximately 0 atomic % near the depth D=D1 because the inorganic solid electrolyte layer 2 contains phosphorus, which is a characteristic element, as a constituent element, whereas the surface layer 1Z, the intermediate layer 1Y, and the lithium metal layer 1X each contain almost no phosphorus, which is a characteristic element, as a constituent element.

[0065] As described above, the changes in the abundances ML, MO, MC, and MP have been described when the inorganic solid electrolyte layer 2 contains amorphous LiPO. However, depending on the composition of the inorganic solid electrolyte layer 2, the abundances ML, MO, MC, and MP may exhibit different behaviors.

[0066] Specifically, when the content of lithium in the inorganic solid electrolyte layer 2 is large, the abundance ML decreases near the depth D=D1 and then increases.

[0067] Furthermore, when the inorganic solid electrolyte layer 2 contains carbon as a constituent element, the abundance MC, which is initially greater than 0 atomic %, temporarily increases in the vicinity of the depth D=D1.

[0068] The conditions for elemental analysis of the negative electrode using XPS are as follows. The analytical device used is an X-ray photoelectron spectrometer (scanning X-ray photoelectron spectrometer PHI5000 VersaProbe manufactured by ULVAC-PHI, Inc.). The internal environmental conditions of the analysis room are not particularly limited, but specifically, 1.5 × 10 -6The etching process is carried out under ultra-high vacuum conditions of 0.1 Pa or less. The sputtering rate during the etching process is not particularly limited, but specifically, it is set to 3.2 mm / min in terms of silicon dioxide (SiO2). Other analytical conditions are: X-ray source = monochromated Al Kα ray (1486.6 eV), X-ray spot diameter = 100 μm, sputtering conditions = Ar + ,1kV,1mm×mm, charge neutralization=none.

[0069] [Physical Properties] As shown in FIG. 2, the results of elemental analysis in the depth direction P of the negative electrode (active material layer 1 and inorganic solid electrolyte layer 2) using XPS satisfy the conditions described below.

[0070] The abundance ratio Z1 (=ML / MC), which is the ratio of the abundance ML to the abundance MC, is greater than 2 at any position (depth D) within the surface layer 1Z (region β, which is the range from point A to point B). That is, in the surface layer 1Z, the abundance ML is sufficiently greater than the abundance MC. As a result, a sufficient amount of lithium is present inside the surface layer 1Z, but almost no carbon is present.

[0071] The reason why the abundance ratio Z1 is greater than 2 at any depth D within the surface layer 1Z is that the area occupied by lithium is sufficiently increased relative to the area occupied by carbon within the surface layer 1Z, thereby suppressing an increase in the interface resistance R due to the presence of a high-resistance component. The high-resistance component described here is, as described above, a carbon-containing component such as lithium carbonate.

[0072] Therefore, when the above-described condition regarding the abundance ratio Z1 is satisfied, the interface resistance R is reduced compared to when the condition regarding the abundance ratio Z1 is not satisfied, thereby improving the ionic conductivity between the active material layer 1 and the inorganic solid electrolyte layer 2.

[0073] The reason why the abundance ratio Z1 is greater than 2 at any depth D within the range of the surface layer 1Z is that, as described above, the rolling treatment of the precursor 3 is used in the process of producing the negative electrode to form the active material layer 1. The reason why the abundance ratio Z1 is greater than 2 as a result of using the rolling treatment of the precursor 3 will be described later.

[0074] The abundance ratio Z1 can be calculated based on the photoelectron spectra (lithium spectrum S1 and carbon spectrum S3) shown in FIG.

[0075] Specifically, when calculating the abundance ratio Z1, the abundances ML and MC are respectively specified within the range (region β) of the surface layer 1Z, and then the abundance ratio Z1 is calculated based on the abundances ML and MC.

[0076] In order to confirm whether the abundance ratio Z1 is greater than 2 at any depth D within the surface layer 1Z, the abundance ratio Z1 is calculated based on the minimum value of the abundance ML and the maximum value of the abundance MC within the surface layer 1Z, and then it is checked whether the abundance ratio Z1 is greater than 2.

[0077] As a result, when the abundance ratio Z1 is greater than 2, the condition that the abundance ratio Z1 is greater than 2 at any depth D within the range of the surface layer 1Z is satisfied. On the other hand, when the abundance ratio Z1 is 2 or less, the condition that the abundance ratio Z1 is greater than 2 at any depth D within the range of the surface layer 1Z is not satisfied.

[0078] [Other physical properties] Within the surface layer 1Z (region β), the abundance ratio Z2 (=MO / MC), which is the ratio of the abundance MO to the abundance MC, is not particularly limited.

[0079] In particular, it is preferable that the abundance ratio Z2 is greater than Z3 at any position (depth D) within the surface layer 1Z. This is because the oxygen occupation area is sufficiently increased relative to the carbon occupation area within the surface layer 1Z, thereby further suppressing an increase in the interface resistance R due to the presence of high-resistance components.

[0080] The abundance ratio Z2 can be calculated based on the photoelectron spectra (oxygen spectrum S2 and carbon spectrum S3) shown in Fig. 2. Specifically, when calculating the abundance ratio Z2, the abundances MO and MC are each specified within the range (region β) of the surface layer 1Z, and then the abundance ratio Z2 is calculated based on the abundances MO and MC.

[0081] In order to confirm whether the abundance ratio Z2 is greater than 3 at any depth D within the range of the surface layer 1Z, the abundance ratio Z2 is calculated based on the minimum value of the abundance MO and the maximum value of the abundance MC within the range of the surface layer 1Z, and then it is checked whether the abundance ratio Z2 is greater than 3.

[0082] As a result, when the abundance ratio Z2 is greater than 3, the condition that the abundance ratio Z2 is greater than 3 at any depth D within the range of the surface layer 1Z is satisfied. On the other hand, when the abundance ratio Z2 is 3 or less, the condition that the abundance ratio Z2 is greater than 3 at any depth D within the range of the surface layer 1Z is not satisfied.

[0083] [Surface layer composition] As described above, in the manufacturing process of the negative electrode, the precursor 3 is rolled to form the active material layer 1. As a result, the surface layer 1Z is stretched during the rolling process of the precursor 3, and therefore the thickness T2 of the surface layer 1Z is sufficiently small.

[0084] Specifically, the thickness T2 is preferably 100 nm or less because the thickness T2 of the extra layer interposed between the intermediate layer 1Y and the inorganic solid electrolyte layer 2, i.e., the surface layer 1Z containing a high-resistance component, becomes sufficiently small, thereby further reducing the interface resistance R.

[0085] [Thickness determination procedure] The procedures for determining the thicknesses T1, T2, and T3 are as described below.

[0086] (Procedure for determining thickness T2) When determining the thickness T2 of the surface layer 1Z, the depths D1 and D2 are determined based on the photoelectron spectrum shown in FIG. 2, and then the thickness T2 is calculated based on the formula T2=D2-D1.

[0087] (Procedure for determining thickness T3) When determining the thickness T3 of the inorganic solid electrolyte layer 2, the depth D1 is determined based on the photoelectron spectrum shown in Fig. 2. As a result, T3 = D1, and therefore the thickness T3 is determined based on the depth D1.

[0088] When specifying the thickness T3, an electron microscope photograph may be used instead of the result of elemental analysis by XPS (photoelectron spectrum).

[0089] Specifically, first, the negative electrode is cut using a cutting tool such as a microtome to expose the cross section of the negative electrode. In this case, the negative electrode is cut in the depth direction P so that the cross sections of the active material layer 1 and the inorganic solid electrolyte layer 2 are exposed.

[0090] Next, an electron microscope is used to observe the cross section of the negative electrode to obtain an electron microscope photograph. This electron microscope is one or more of a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The observation magnification can be set arbitrarily as long as it allows observation of both the active material layer 1 and the inorganic solid electrolyte layer 2 in the depth direction P.

[0091] Finally, the thickness T3 of the inorganic solid electrolyte layer 2 is measured based on the electron microscope photograph. In this case, the thickness T3 of the inorganic solid electrolyte layer 2 is measured at 10 different locations, and then the average value of the 10 thicknesses T3 is calculated.

[0092] As will be described later, in the process of manufacturing the negative electrode, the inorganic solid electrolyte layer 2 is formed on the active material layer 1 using a vapor phase film formation method or the like, and therefore an interface, which is a physical boundary, exists between the active material layer 1 and the inorganic solid electrolyte layer 2. As a result, in an electron microscope photograph, the boundary between the active material layer 1 and the inorganic solid electrolyte layer 2 can be seen based on the position of the interface, and therefore the thickness T3 can be measured based on the position of the interface.

[0093] (Procedure for determining thickness T1) When determining the thickness T1 of the lithium metal layer 1X, the depth D3 is determined based on the photoelectron spectrum shown in Fig. 2. This depth D3 corresponds to the sum of the thickness T3 of the inorganic solid electrolyte layer 2, the thickness T2 of the surface layer 1Z, and the thickness of the intermediate layer 1Y.

[0094] If the position of point C (depth D) and the position of point D (depth D) do not coincide with each other, the depth D3 is determined based on either point C or D located on the side with the greater depth D.

[0095] Thereafter, the depth D3 is subtracted from the thickness of the entire negative electrode to calculate the thickness T1.

[0096] <1-3. Operation> At the negative electrode, during the electrode reaction, lithium is released in an ionic state from the lithium metal layer 1X contained in the active material layer 1 via the inorganic solid electrolyte layer 2, and the lithium is absorbed in an ionic state into the lithium metal layer 1X via the inorganic solid electrolyte layer 2.

[0097] <1-4. Manufacturing method> 3, 4, and 5 each show a cross-sectional configuration corresponding to FIG. 1 to explain the method for manufacturing a negative electrode. Each of FIGS. 6 and 7 shows an enlarged cross-sectional configuration of a portion (portion N) of precursor 3 used in the method for manufacturing a negative electrode. Note that FIG. 6 corresponds to FIG. 3, and FIG. 7 corresponds to FIG. 4. Each of FIGS. 6 and 7 also shows protective film 4.

[0098] [Preparation of precursor] When manufacturing a negative electrode, first, a precursor 3 is prepared as shown in Fig. 3. This precursor 3 is a mass of lithium metal, a so-called lithium ingot, used to form the active material layer 1. However, the precursor 3 may also be a foil-shaped lithium metal (lithium foil).

[0099] Specifically, precursor 3 has a structure similar to that of active material layer 1, except that precursor 3 has a thickness greater than that of active material layer 1. That is, precursor 3 has a structure in which lithium metal layer 1X, intermediate layer 1Y, and surface layer 1Z are laminated in this order, as shown in Fig. 6, and the details of lithium metal layer 1X, intermediate layer 1Y, and surface layer 1Z are as described above.

[0100] However, the thickness T2 of the surface layer 1Z in the precursor 3 is sufficiently larger than the thickness T2 of the surface layer 1Z in the finally produced active material layer 1. This is because, in the precursor 3 stored in a normal environment such as the atmosphere, the lithium reacts with oxygen, carbon dioxide, water, and the like near the surface of the lithium metal layer 1X, as described above, and thus the thickness T2 increases.

[0101] There is no particular limitation on the method for preparing the precursor 3. As an example, a method for preparing a foil-shaped precursor 3 is as described below.

[0102] Specifically, the lithium foil may be etched by irradiating the surface of the lithium foil with an inert ion gas in a vacuum atmosphere, thereby reducing the thickness of the lithium foil and obtaining a foil-shaped precursor 3.

[0103] Alternatively, a lithium ingot may be melted inside the glove box. This produces a lithium foil, thereby producing a foil-shaped precursor 3. The conditions of the atmosphere inside the glove box are not particularly limited and can be set arbitrarily. For example, the atmosphere may be an argon gas atmosphere with an oxygen concentration of 0.2 ppm and a temperature of 250°C or higher.

[0104] [Formation of active material layer (rolling treatment of precursor)] Next, the precursor 3 is rolled in the thickness direction in a reduced pressure environment or an inert gas atmosphere. Hereinafter, the reduced pressure environment or the inert gas atmosphere will also be simply referred to as "the environment."

[0105] The conditions of the reduced pressure environment are not particularly limited, but specifically, the pressure is 1×10 -1 It is preferable that the inert gas atmosphere is a vacuum of 0.2 Pa or less. Specific examples of the inert gas used in the inert gas atmosphere include one or more of argon gas, helium gas, and krypton gas. The conditions of the inert gas atmosphere are not particularly limited, but specifically, the oxygen concentration is preferably 0.2 ppm or less. In particular, it is preferable that the inert gas contains argon gas. This is because, during the rolling process of the precursor 3, new high-resistance components are less likely to be formed on the surface of the precursor 3.

[0106] To ensure both the reduced pressure environment and the inert gas atmosphere, a sealed chamber is used in which conditions such as pressure, gas type, and oxygen concentration can be set arbitrarily. Specific examples of sealed chambers include a glove box and a vacuum device.

[0107] 3, a pair of protective films 4 is prepared in the same environment, and then the precursor 3 is placed between the pair of protective films 4. In this case, each of the pair of protective films 4 is brought into close contact with the precursor 3, so that the pair of protective films 4 face each other with the precursor 3 interposed therebetween.

[0108] The protective film 4 is a protective member that physically and chemically protects the surface of the precursor 3 during a rolling process described later, and contains a polymer compound. The thickness of the protective film 4 is not particularly limited and can be set arbitrarily.

[0109] The type of polymer compound is not particularly limited, but is preferably one or more types of polyolefins, because polyolefins have low reactivity with the precursor 3 (lithium metal), and therefore when the protective film 4 is adhered to the precursor 3 during the rolling process, deterioration of the precursor 3 due to a chemical reaction between the precursor 3 and the protective film 4 is suppressed.

[0110] Specifically, when the protective film 4 contains a polymer compound that has high reactivity with the precursor 3 (lithium metal), the protective film 4 is more likely to react with lithium metal during the rolling process.

[0111] In this case, the reaction between the protective film 4 and the lithium metal tends to form impurities, i.e., high-resistance by-products, on the surface of the precursor 3, and the color of the precursor 3 tends to change from silvery white to black, which tends to cause deterioration near the surface of the precursor 3. As a result, when the inorganic solid electrolyte layer 2 is formed on the active material layer 1 in a later step, the interface resistance R tends to increase.

[0112] On the other hand, if the protective film 4 contains a polymer compound that has low reactivity with the precursor 3 (lithium metal), the protective film 4 is less likely to react with lithium metal during the rolling process.

[0113] In this case, high-resistance by-reaction products are less likely to be formed on the surface of the precursor 3, and the color of the precursor 3 is less likely to change from silver-white to black, making the precursor 3 less likely to deteriorate near the surface. As a result, when the inorganic solid electrolyte layer 2 is formed on the active material layer 1, the interface resistance R is less likely to increase.

[0114] Specific examples of polyolefins include polyethylene and polypropylene, etc. For reference, specific examples of polymer compounds having high reactivity with the precursor 3 (lithium metal) are Teflon (registered trademark) and Kapton, etc.

[0115] After the precursor 3 is placed between the pair of protective films 4, the precursor 3 is rolled as shown in Fig. 4. Specifically, in the same environment, the precursor 3 is pressed via the pair of protective films 4 in the direction in which the pair of protective films 4 face each other (thickness direction of the precursor 3), thereby rolling the precursor 3. In this case, it is not necessary to use a lubricant.

[0116] Here, a roll press is used to perform the rolling process on the precursor 3. This roll press is equipped with a pair of rollers 5 that are movable in a movement direction F, and each roller 5 is rotatable about a rotation axis J that extends in a direction intersecting the movement direction F.

[0117] In this case, the precursor 3 and the pair of protective films 4 are placed between a pair of rollers 5, and the pair of rollers 5 are brought into close contact with the pair of protective films 4. That is, the roller 5 located above the precursor 3 is brought into close contact with the protective film 4 located above the precursor 3. The roller 5 located below the precursor 3 is brought into close contact with the protective film 4 located below the precursor 3.

[0118] In the rolling process of the precursor 3, each of the pair of rollers 5 rotates about the rotation axis J, and the pair of rollers 5 moves in the movement direction F while pressing the precursor 3 via the pair of protective films 4 in a direction in which the pair of protective films 4 face each other. That is, the upper roller 5 moves in the movement direction F while pressing the precursor 3 via the upper protective film 4. Furthermore, the lower roller 5 moves in the movement direction F while pressing the precursor 3 via the lower protective film 4.

[0119] When rolling the precursor 3, the precursor 3 may be crushed in advance using a tool such as a pestle to make it easier to roll the precursor 3 using a roll press (a pair of rollers 5).

[0120] As a result, the precursor 3 is stretched, and is formed into a thin sheet shape.

[0121] 7, not only the lithium metal layer 1X but also the surface layer 1Z is stretched, so that the thickness T1 of the lithium metal layer 1X is reduced, and the thickness T2 of the surface layer 1Z is also reduced. In this case, the thickness of the intermediate layer 1Y may also be reduced.

[0122] When the surface layer 1Z is stretched, the thickness T2 of the surface layer 1Z is reduced, and accordingly, high-resistance components such as lithium carbonate present on the surface of the intermediate layer 1Y are removed. As a result, the amount of the surface layer 1Z covering the surface of the intermediate layer 1Y is reduced, and the amount of high-resistance components present inside the surface layer 1Z is also reduced. As a result, the above-mentioned condition regarding the abundance ratio Z1 is satisfied, and the thickness T2 becomes 100 nm or less. Therefore, when the inorganic solid electrolyte layer 2 is formed on the active material layer 1 in a subsequent process, the interface resistance R is reduced.

[0123] When the precursor 3 is rolled using a roll press, the rolling process is continued until the thickness of the precursor 3 reaches a desired thickness. This rolling process may be repeated once or twice or more times.

[0124] After the rolling process of the precursor 3 is completed, the pair of protective films 4 are removed by peeling them off from the rolled precursor 3. As a result, an active material layer 1 including a lithium metal layer 1X, an intermediate layer 1Y, and a surface layer 1Z is formed, as shown in FIGS.

[0125] In the elemental analysis results of the outermost surface of surface layer 1Z using XPS after forming active material layer 1 and before forming inorganic solid electrolyte layer 2, it is preferable that the abundance ML is larger than each of the abundances MO and MC. This is because when inorganic solid electrolyte layer 2 is formed on active material layer 1 in a later step, the abundance of high-resistance components at the interface between active material layer 1 and inorganic solid electrolyte layer 2 decreases, and therefore interface resistance R is sufficiently reduced.

[0126] [Formation of inorganic solid electrolyte layer] Finally, in the same environment, the inorganic solid electrolyte layer 2 is formed on the surface layer 1Z of the active material layer 1.

[0127] The method for forming the inorganic solid electrolyte layer 2 is not particularly limited, but specifically, it is preferable to form the inorganic solid electrolyte layer 2 using one or more vapor phase film formation methods, because this makes it easier to form the inorganic solid electrolyte layer 2 stably and with good reproducibility while suppressing the formation of new high-resistance components on the surface of the active material layer 1.

[0128] Specific examples of vapor deposition methods include vacuum evaporation, sputtering, pulsed laser deposition (PLD), atomic layer deposition (ALD), and chemical vapor deposition (CVD).

[0129] When forming the inorganic solid electrolyte layer 2, it is preferable to form the active material layer 1 in the same environment, and then subsequently form the inorganic solid electrolyte layer 2 in the same environment without exposing the active material layer 1 to the air. That is, when the active material layer 1 is formed inside a sealed chamber, it is preferable to subsequently form the inorganic solid electrolyte layer 2 inside the sealed chamber. This is because the formation of new high-resistance components on the surface of the active material layer 1 is suppressed, and the interface resistance R is further reduced.

[0130] Specifically, when the active material layer 1 is exposed to the air after its formation, as described above, lithium near the surface of the lithium metal layer 1X is more likely to react with oxygen, carbon dioxide, water, and the like in the air. In this case, even though the thickness T2 has been reduced by the rolling treatment, the thickness T2 increases again before the inorganic solid electrolyte layer 2 is formed. This makes it easier for the interface resistance R to increase when the inorganic solid electrolyte layer 2 is formed.

[0131] In contrast, if the inorganic solid electrolyte layer 2 is formed in the same environment as the active material layer 1 without exposing the active material layer 1 to the atmosphere after the active material layer 1 is formed, lithium is less likely to react with oxygen, carbon dioxide, water, etc. near the surface of the lithium metal layer 1X, and the thickness T2 tends to be maintained without excessive increase. As a result, the interface resistance R tends to decrease when the inorganic solid electrolyte layer 2 is formed.

[0132] In this case, it is preferable to form the inorganic solid electrolyte layer 2 quickly after forming the active material layer 1, because this will result in a sufficient decrease in interface resistance R.

[0133] The inter-step time, which is the time from the formation of the active material layer 1 until the formation of the inorganic solid electrolyte layer 2, is not particularly limited, but is preferably within 2 hours. This is because, even in a reduced pressure environment or an inert gas atmosphere, lithium present near the surface of the lithium metal layer 1X is likely to react with oxygen, carbon dioxide, water, and the like present in trace amounts in the environment, and the inter-step time is sufficiently short, so that the thickness T2 tends to be maintained without excessive increase. This makes it easier to reduce the interfacial resistance R when the inorganic solid electrolyte layer 2 is formed.

[0134] If, for some reason, it is necessary to store the active material layer 1 after its formation and before the inorganic solid electrolyte layer 2 is formed, it is preferable to store the active material layer 1 in the same environment, since the thickness T2 of the active material layer 1 is likely to be sufficiently maintained even during storage.

[0135] The conditions of the reduced pressure environment during storage of the active material layer 1 are not particularly limited. Specifically, if the storage period is within one day, the pressure is 1×10 -1 However, if the storage period of the active material layer 1 exceeds one day, the pressure should be 1×10 -4 It is preferable that the vacuum is equal to or less than Pa. Details regarding the inert gas atmosphere are as described above.

[0136] As a result, the inorganic solid electrolyte layer 2 is formed on the active material layer 1 (lithium metal layer 1X, intermediate layer 1Y and surface layer 1Z), thereby completing the negative electrode.

[0137] <1-5. Actions and Effects> The negative electrode and the method for producing the same provide the following functions and effects.

[0138] [Negative electrode] The negative electrode includes an active material layer 1 (lithium metal layer 1X, intermediate layer 1Y, and surface layer 1Z) and an inorganic solid electrolyte layer 2. The intermediate layer 1Y contains lithium and oxygen as constituent elements, the surface layer 1Z contains lithium, oxygen, and carbon as constituent elements, and the inorganic solid electrolyte layer 2 contains a characteristic element. Elemental analysis of the negative electrode (active material layer 1 and inorganic solid electrolyte layer 2) in the depth direction P using XPS showed that the abundance ratio Z1 of the abundances ML and MC was greater than 2 at any depth D within the range (region β) of the surface layer 1Z.

[0139] In this case, as described above, an increase in interface resistance R due to the presence of a high-resistance component (carbon-containing component) such as lithium carbonate is suppressed near the interface between the active material layer 1 and the inorganic solid electrolyte layer 2. Therefore, the interface resistance R is lower than when the condition regarding the abundance ratio Z1 described above is not satisfied, and excellent electrical characteristics can be obtained.

[0140] This improves ionic conductivity between the active material layer 1 and the inorganic solid electrolyte layer 2. Therefore, excellent ionic conductivity can be obtained in the negative electrode without providing a separate ion-conducting layer containing lithium nitride or the like on the surface of the active material layer 1.

[0141] In particular, if the abundance ratio Z2 of the abundances MO and MC is greater than 3 at any depth D within the surface layer 1Z (region β), the interface resistance R will be further reduced, resulting in a greater effect.

[0142] Furthermore, if the thickness T2 of the surface layer 1Z is 100 nm or less, the interface resistance R is further reduced, and therefore a greater effect can be obtained.

[0143] Furthermore, if the thickness T1 of the lithium metal layer 1X is 10 μm to 1000 μm, the lithium metal layer 1X can release and store a sufficient amount of lithium in an ionic state, thereby achieving a greater effect.

[0144] Furthermore, if the inorganic solid electrolyte layer 2 contains lithium, oxygen, and a characteristic element (phosphorus) as constituent elements and the lithium content in the inorganic solid electrolyte layer 2 is 10 atomic % to 60 atomic %, the inorganic solid electrolyte layer 2 can easily function sufficiently as a protective film and a lithium supply source, thereby achieving a greater effect.

[0145] Furthermore, if the thickness T3 of the inorganic solid electrolyte layer 2 is 10 nm to 20,000 nm, the inorganic solid electrolyte layer 2 can function sufficiently as a protective film and a lithium supply source, thereby achieving a greater effect.

[0146] [Method of manufacturing negative electrode] The precursor 3 (lithium metal layer 1X, intermediate layer 1Y and surface layer 1Z) is rolled in a reduced pressure environment or an inert gas atmosphere to form an active material layer 1, and then the inorganic solid electrolyte layer 2 is formed on the surface layer 1Z of the active material layer 1.

[0147] As a result, as described above, the thickness T2 of the surface layer 1Z is reduced Z by utilizing the rolling treatment of the precursor 3, and high-resistance components such as lithium carbonate contained in the surface layer 1Z are removed, thereby reducing the interface resistance R and making it possible to obtain a negative electrode with excellent electrical properties.

[0148] In this case, the negative electrode is manufactured by only simple processes, namely, rolling the precursor 3 and forming the inorganic solid electrolyte layer 2. Therefore, it is not necessary to use complicated processes such as treating the lithium metal foil with an acid solution or etching, and therefore a negative electrode with excellent electrical properties can be easily obtained.

[0149] In particular, if the active material layer 1 is formed in a reduced pressure environment or an inert gas atmosphere, and then the inorganic solid electrolyte layer 2 is subsequently formed in the same environment without exposing the active material layer 1 to the air, the formation of new high-resistance components on the surface of the active material layer 1 is suppressed, thereby further reducing the interface resistance R and achieving a greater effect.

[0150] Furthermore, if the precursor 3 is placed between a pair of protective films 4 (polyolefin) in a reduced pressure environment or an inert gas atmosphere, and then pressed against the precursor 3 via the pair of protective films 4 in the same environment, deterioration (alteration and discoloration) of the precursor 3 during the rolling process is suppressed. This further reduces the interface resistance R, thereby achieving a greater effect.

[0151] Furthermore, if the elemental analysis results of the outermost surface of surface layer 1Z using XPS after forming active material layer 1 and before forming inorganic solid electrolyte layer 2 show that the abundance ML is greater than the abundances MO and MC, respectively, the abundance of high-resistance components decreases at the interface between active material layer 1 and inorganic solid electrolyte layer 2. Therefore, the interface resistance R is sufficiently reduced, and a greater effect can be obtained.

[0152] In addition, the pressure in the reduced pressure environment is 1×10 -1 If the pressure is 0.05 Pa or less, high resistance components are less likely to be newly formed on the surface of the precursor 3 during the rolling process, thereby achieving a higher effect. Furthermore, if the inert gas atmosphere contains argon gas and the oxygen concentration in the inert gas atmosphere is 0.2 ppm or less, high resistance components are less likely to be newly formed on the surface of the precursor 3 during the rolling process, thereby achieving a higher effect.

[0153] Furthermore, if the inorganic solid electrolyte layer 2 is formed using a vapor phase film formation method, the inorganic solid electrolyte layer 2 can be formed stably and with good reproducibility while suppressing the formation of new high-resistance components on the surface of the active material layer 1, thereby achieving a greater effect.

[0154] <2.Battery> Next, a battery according to an embodiment of the present technology will be described as an example of an electrochemical device using the above-described negative electrode.

[0155] The battery described herein includes a positive electrode and a negative electrode, and may be a primary battery or a secondary battery, as described above.

[0156] <2-1.Configuration> Figure 8 shows the cross-sectional structure of the battery, but only shows the main parts of the battery involved in the battery reaction (electrode reaction).

[0157] As shown in Fig. 8, this battery includes a positive electrode 10, a negative electrode 20, and an electrolyte 30. The type of battery (the principle of the battery reaction) described here is not particularly limited. Therefore, the battery may be a lithium battery, a lithium-sulfur battery, or a lithium-air battery.

[0158] [Positive electrode] The positive electrode 10 faces the negative electrode 20 via the electrolyte 30. The configuration of the positive electrode 10 varies depending on the type of battery.

[0159] When the battery is a lithium battery, the positive electrode 10 contains one or more lithium-containing compounds as a positive electrode active material. The lithium-containing compounds are compounds containing lithium and one or more transition metal elements as constituent elements, and more specifically, oxides, phosphate compounds, silicate compounds, borate compounds, etc. Specific examples of oxides include LiNiO2, LiCoO2, LiMn2O4, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and Li4Ti5O 12 Specific examples of phosphate compounds include LiFePO4 and LiMnPO4.

[0160] In this case, the positive electrode 10 may include a positive electrode current collector and a positive electrode active material layer (not shown), and the positive electrode active material layer may include a positive electrode active material. The positive electrode current collector includes a conductive material such as a metal material, and the positive electrode active material layer is provided on the positive electrode current collector. However, the positive electrode active material layer may further include one or more of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0161] When the battery is a lithium-sulfur battery, the positive electrode 10 contains one or more of sulfur and sulfur compounds as a positive electrode active material. Specific examples of sulfur compounds include lithium sulfide and sulfur-containing polyacrylonitrile (PAN-S).

[0162] When the battery is a lithium-air battery, the positive electrode 10 contains air as the positive electrode active material.

[0163] [Negative electrode] The negative electrode 20 has the same configuration as the negative electrode described above. The negative electrode 20 is disposed such that the inorganic solid electrolyte layer 2 faces the positive electrode 10 with the electrolyte 30 interposed therebetween.

[0164] [Electrolytes] The electrolyte 30 is a medium that transfers lithium in an ionic state between the positive electrode 10 and the negative electrode 20. The electrolyte 30 may be a liquid electrolyte (electrolytic solution) or a solid electrolyte (solid electrolyte) depending on the type of battery.

[0165] When the electrolyte 30 is an electrolytic solution, the electrolytic solution may be impregnated into a separator (not shown). The electrolytic solution contains a solvent and an electrolyte salt. The solvent may be an aqueous solvent or a non-aqueous solvent (organic solvent). The electrolyte salt contains a light metal salt such as a lithium salt. The separator is an insulating porous film interposed between the positive electrode 10 and the negative electrode 20 and contains a polymer compound.

[0166] The battery may be an all-solid-state battery that does not use an electrolytic solution. In this case, the electrolyte 30 may be omitted. This is because the inorganic solid electrolyte layer 2 also functions as the electrolyte 30, and therefore the electrolyte 30 is not necessary.

[0167] [Other components] The battery may further include one or more of the other components not shown, such as an exterior member, a positive electrode lead, and a negative electrode lead.

[0168] The exterior member is a member that houses the positive electrode 10, the negative electrode 20, and the electrolyte 30, and specifically may be a battery can or a bag-shaped film. The positive electrode lead is connected to the positive electrode 10, and the negative electrode lead is connected to the negative electrode 20.

[0169] <2-2. Operation> In this battery, during the battery reaction (electrode reaction), lithium is released in an ionic state from the negative electrode 20, and lithium is absorbed in the negative electrode 20 in an ionic state.

[0170] <2-3. Actions and Effects> This battery includes an anode 20, which has the same configuration as the above-described anode. Therefore, for the reasons described above, excellent electrical characteristics can be obtained. This allows for a high battery capacity and excellent cycle characteristics.

[0171] Other functions and effects of this battery are similar to those of the negative electrode described above.

[0172] <3. Battery uses> The use (application) of the battery is not particularly limited. The battery used as a power source may be a main power source or an auxiliary power source in electronic devices, electric vehicles, etc. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

[0173] Specific examples of battery applications are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power for emergencies. In these applications, one battery or multiple batteries may be used.

[0174] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that runs on a battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the battery. The home power storage system can use the power stored in the battery, which is the power storage source, to power home electrical appliances, etc. [Example]

[0175] An embodiment of the present technology will be described.

[0176] <Experimental Example 1 and Comparative Example 1> As described below, after the negative electrode was fabricated, the characteristics of the negative electrode were evaluated.

[0177] [Preparation of negative electrode] The negative electrode shown in FIG. 1 was fabricated according to the procedures shown in FIGS.

[0178] First, a precursor 3 (a lithium ingot having a thickness of 1 mm) was prepared. As shown in FIG. 6, the precursor 3 included a lithium metal layer 1X (thickness T1), an intermediate layer 1Y, and a surface layer 1Z.

[0179] Next, inside a glove box (inert gas atmosphere), the precursor 3 was placed between a pair of protective films 4 (two polypropylene films with a thickness of 0.15 mm), and then a pestle was used to press the precursor 3 through the protective films 4 to lightly crush the precursor 3. In this case, argon gas was supplied into the glove box to set the oxygen concentration inside the glove box to 0.2 ppm or less.

[0180] Subsequently, the precursor 3 was pressed through the pair of protective films 4 using a roll press equipped with a pair of rollers 5, thereby rolling the precursor 3. In this case, the distance (gap) between the pair of rollers 5 was gradually reduced from 1 mm to 0.1 mm, so that the thickness of the precursor 3 after rolling was set to 0.1 mm.

[0181] Next, the rolled precursor 3 was folded multiple times and then rolled again until the thickness reached 0.1 mm. In this case, the rolling treatment of the precursor 3 was repeated three times. As a result, the precursor 3 was stretched, and an active material layer 1 including a lithium metal layer 1X, an intermediate layer 1Y, and a surface layer 1Z was formed.

[0182] Finally, inside a vacuum RF sputtering apparatus (inert atmosphere), an inorganic solid electrolyte material (amorphous Li3PO4) was deposited on the surface layer 1Z of the active material layer 1 using a sputtering method, thereby forming an inorganic solid electrolyte layer 2.

[0183] In this case, after the active material layer 1 was formed, the active material layer 1 was moved from inside the glove box to inside the vacuum RF sputtering apparatus without being exposed to the atmosphere, and the pressure inside the vacuum RF sputtering apparatus was reduced to 6.0 × 10 -6 It was Pa.

[0184] When forming the inorganic solid electrolyte layer 2, argon gas was supplied into the vacuum RF sputtering device so that the pressure was 0.15 Pa, and a LiPO plate (diameter = 50.8 mm) was used as the target. In this case, the output was set to 100 W.

[0185] As a result, the inorganic solid electrolyte layer 2 was formed on the active material layer 1 (lithium metal layer 1X, intermediate layer 1Y and surface layer 1Z), and thus the negative electrode was completed (Example 1).

[0186] For comparison, a negative electrode was produced in the same manner except that the precursor 3 was not rolled (Comparative Example 1). In this case, a lithium metal foil stored in the air (a dry environment with a dew point temperature of 40°C or less) for three months was used as the active material layer. This active material layer, like the active material layer 1 described above, includes a lithium metal layer 1X, an intermediate layer 1Y, and a surface layer 1Z.

[0187] [Anode characteristic evaluation] The electrical properties of the negative electrode were evaluated according to the procedure described below, and the results shown in Tables 1 and 2, and in FIGS. 2 and 9 were obtained.

[0188] (Elemental analysis of the outermost surface layer using XPS) By the above-described procedure, after the active material layer 1 was formed and before the inorganic solid electrolyte layer 2 was formed, elemental analysis of the outermost surface of the surface layer 1Z was performed using XPS to calculate the abundances ML, MO, and MC (atomic %), and the results shown in Table 1 were obtained.

[0189] (Elemental analysis of the negative electrode in the depth direction using XPS) After the negative electrode was completed according to the above procedure, elemental analysis of the negative electrode in the depth direction P was carried out using XPS, and the results shown in FIGS. 2 and 9 were obtained.

[0190] As described above, Fig. 2 schematically shows the elemental analysis results of Example 1. Fig. 9 schematically shows the elemental analysis results of Comparative Example 1, and corresponds to Fig. 2. However, Fig. 9 does not show points C and D and depth D3 due to the large thickness T2 of surface layer 1Z and the large thickness of intermediate layer 1Y.

[0191] As shown in Figures 2 and 9, elemental analysis of the negative electrode in the depth direction P using XPS detected a lithium spectrum S1, an oxygen spectrum S2, a carbon spectrum S3, and a phosphorus spectrum S4. This indicated that the intermediate layer 1Y contained lithium and oxygen as constituent elements. The surface layer 1Z contained lithium, oxygen, and carbon as constituent elements. The inorganic solid electrolyte layer 2 contained lithium, oxygen, and a characteristic element (phosphorus) as constituent elements.

[0192] (abundance ratio Z1,Z2) According to the above-described procedure, the abundances ML and MC (atomic %) were determined based on the elemental analysis results in the depth direction P of the negative electrode shown in FIGS. 2 and 9, respectively, and then the abundance ratio Z1 was calculated, and the results shown in Table 2 were obtained.

[0193] Furthermore, by the above-described procedure, the abundances MO and MC (atomic %) were identified based on the elemental analysis results in the depth direction P of the negative electrode shown in Figure 2 and Figure 9, respectively, and then the abundance ratio Z2 was calculated, and the results shown in Table 2 were obtained.

[0194] (Thickness T2) The thickness T2 (nm) was determined based on the elemental analysis results (FIGS. 2 and 9) of the negative electrode in the depth direction P using the above-described procedure, and the results shown in Table 2 were obtained.

[0195] (interface resistance R) To investigate the electrical resistance characteristics of the negative electrode, the interfacial resistance R (Ω cm 2 ) was calculated, and the results shown in Table 2 were obtained.

[0196] Fig. 10 shows a cross-sectional configuration corresponding to Fig. 1 to explain a method for measuring the interfacial resistance R. When measuring the interfacial resistance R, as shown in Fig. 10, a measurement electrode 6 was formed on the inorganic solid electrolyte layer 2, and then the AC impedance (amplitude voltage = 50 mV) of the negative electrode was measured using the measurement electrode 6 together with a pair of resistance measurement probes (not shown).

[0197] When forming the measurement electrode 6, after the negative electrode was prepared, the negative electrode was moved from the inside of the vacuum RF sputtering apparatus to the inside of the vacuum deposition apparatus without being exposed to the atmosphere, and the pressure inside the vacuum deposition apparatus was reduced to 1.0 × 10 -6 The pressure was lowered until it reached Pa. Thereafter, lithium metal was deposited on the surface of the inorganic solid electrolyte layer 2 by vacuum deposition to form a measuring electrode 6 (diameter = 0.5 mm).

[0198] When measuring the interface resistance R, one probe was connected to the lithium metal layer 1X, and the other probe was connected to the measurement electrode 6. In addition, a Cole-Cole plot was obtained based on the measurement results of the AC impedance, and then the interface resistance R was calculated based on the Cole-Cole plot.

[0199] [Table 1]

[0200] [Table 2]

[0201] [Consideration] As shown in Tables 1 and 2, the electrical properties of the negative electrodes varied greatly depending on the construction and physical properties of the negative electrodes.

[0202] Specifically, when the precursor 3 was not subjected to rolling treatment (Comparative Example 1), the interface resistance R was 500 Ω·cm 2 In contrast, when the precursor 3 was subjected to rolling treatment (Example 1), the interface resistance R increased to 80 Ω cm2 It dropped to.

[0203] As a result, the electrical resistance of the entire negative electrode when the precursor 3 was rolled was about one-third of the electrical resistance of the entire negative electrode when the precursor 3 was not rolled. Therefore, when a battery is fabricated using the negative electrode, the battery can be charged or discharged at about three times the current value.

[0204] When the precursor 3 was not rolled (Comparative Example 1), the thickness T2 was greater than 300 nm. In contrast, when the precursor 3 was rolled (Example 1), the thickness T2 was 100 nm or less, more specifically, 70 nm.

[0205] Furthermore, when the precursor 3 was not rolled (Comparative Example 1), the abundance ML was smaller than the abundances MO and MC at the time of forming the active material layer 1. In contrast, when the precursor 3 was rolled (Example 1), the abundance ML was larger than the abundances MO and MC at the time of forming the active material layer 1.

[0206] Furthermore, when the precursor 3 was not rolled (Comparative Example 1), the abundance ratio Z1 was 2 or less and the abundance ratio Z2 was 3 or less at all depths D within the range of the surface layer 1Z, resulting in an increase in the interface resistance R. In contrast, when the precursor 3 was rolled (Example 1), the abundance ratio Z1 was greater than 2 and the abundance ratio Z2 was greater than 3 at all depths D within the range of the surface layer 1Z, resulting in a decrease in the interface resistance R.

[0207] [summary] 2 and 9, when the negative electrode includes an active material layer 1 (lithium metal layer 1X, intermediate layer 1Y, and surface layer 1Z) and an inorganic solid electrolyte layer 2, the intermediate layer 1Y contains lithium and oxygen as constituent elements, the surface layer 1Z contains lithium, oxygen, and carbon as constituent elements, the inorganic solid electrolyte layer 2 contains a characteristic element, and the abundance ratio Z1 is greater than 2 at any depth D within the surface layer 1Z, the interface resistance R decreases. Therefore, excellent electrical properties (electrical resistance properties) could be obtained in the negative electrode.

[0208] Furthermore, the manufacturing procedure for the negative electrode using the rolling treatment of the precursor 3 made it possible to obtain a negative electrode having excellent electrical properties (electrical resistance properties).

[0209] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0210] Specifically, the case where the characteristic element contained in the inorganic solid electrolyte layer is phosphorus has been described, but the type of the characteristic element is not particularly limited, and an element other than phosphorus may be used. Details regarding the characteristic element other than phosphorus are as described above.

[0211] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. an active material layer; an inorganic solid electrolyte layer provided on the active material layer; Equipped with The active material layer is, in order from the side farther from the inorganic solid electrolyte layer, a lithium metal layer; an intermediate layer containing lithium and oxygen as constituent elements; a surface layer containing lithium, oxygen, and carbon as constituent elements; Including, the inorganic solid electrolyte layer contains a characteristic element different from lithium, oxygen, and carbon as a constituent element, a ratio of the amount of lithium present to the amount of carbon present in a depth direction of the active material layer and the inorganic solid electrolyte layer obtained by X-ray photoelectron spectroscopy is greater than 2 at any depth within a range from a first intersection point where a spectrum derived from the characteristic element and a spectrum derived from carbon intersect with each other to a second intersection point where a spectrum derived from lithium and a spectrum derived from oxygen intersect with each other; Negative electrode.

2. a ratio of the amount of oxygen to the amount of carbon in a depth direction of the active material layer and the inorganic solid electrolyte layer obtained by X-ray photoelectron spectroscopy is greater than 3 at any depth within a range from the first intersection point to the second intersection point; The negative electrode according to claim 1 .

3. The thickness of the surface layer is 100 nm or less. The negative electrode according to claim 1 .

4. The thickness of the lithium metal layer is 10 μm or more and 1000 μm or less. The negative electrode according to claim 1 .

5. the inorganic solid electrolyte layer contains lithium, oxygen, and the characteristic element phosphorus as constituent elements, the content of lithium in the inorganic solid electrolyte layer is 10 atomic % or more and 60 atomic % or less; The negative electrode according to claim 1 .

6. The thickness of the inorganic solid electrolyte layer is 10 nm or more and 20,000 nm or less. The negative electrode according to claim 1 .

7. preparing a precursor in which a lithium metal layer, an intermediate layer containing lithium and oxygen as constituent elements, and a surface layer containing lithium, oxygen, and carbon as constituent elements are laminated in this order; rolling the precursor in a reduced pressure environment or an inert gas atmosphere to form an active material layer including the lithium metal layer, the intermediate layer, and the surface layer; forming an inorganic solid electrolyte layer on the surface layer of the active material layer in the reduced pressure environment or the inert gas atmosphere; A method for manufacturing a negative electrode.

8. After forming the active material layer in the reduced pressure environment or the inert gas atmosphere, the inorganic solid electrolyte layer is subsequently formed in the reduced pressure environment or the inert gas atmosphere without exposing the active material layer to the air. The method for producing the negative electrode according to claim 7.

9. In the reduced pressure environment or the inert gas atmosphere, the precursor is placed between a pair of protective members, and then the precursor is rolled by pressing the precursor via the pair of protective members in directions in which the pair of protective members face each other; Each of the pair of protective members contains polyolefin. The method for producing a negative electrode according to claim 7 .

10. and in a result of elemental analysis of the outermost surface of the surface layer using X-ray photoelectron spectroscopy after the formation of the active material layer and before the formation of the inorganic solid electrolyte layer, the amount of lithium present is greater than the amount of oxygen present and the amount of carbon present. The method for producing a negative electrode according to claim 7 .

11. The pressure of the reduced pressure environment is 1×10 -1 Pa or less, The inert gas atmosphere contains argon gas, and the concentration of oxygen in the inert gas atmosphere is 0.2 ppm or less. The method for producing a negative electrode according to claim 7 .

12. forming the inorganic solid electrolyte layer using a vapor phase deposition method; The method for producing the negative electrode according to any one of claims 7 to 11.

13. A positive electrode and The negative electrode according to any one of claims 1 to 6, Equipped with a battery.

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