Negative electrode composite and secondary battery

Abstract

The present invention addresses the problem of providing a countermeasure against deposition of an alkali metal in cases where the alkali metal is used as a negative electrode. The above-described problem is solved by a negative electrode composite body that contains: a negative electrode active material which contains, as main components, Li and an element M that is solid soluble in Li; and a substance X which has a higher redox potential than the negative electrode active material, or a substance X which does not have electrode activity.

Description

[Technical Field]

[0001] The present invention relates to an anode composite and a secondary battery. More specifically, the present invention relates to an anode composite including an anode active material containing, as main components, Li and an element M that is solid-soluble in Li, and a substance X that has a higher redox potential than the anode active material or has no electrode activity, and a secondary battery including the same. [Background technology]

[0002] BACKGROUND ART In recent years, there has been an increasing demand for lithium ion secondary batteries for storing electric power in automobiles such as electric vehicles and hybrid vehicles, and in power generation devices such as solar cells and wind power generators. Furthermore, from the perspective of ensuring safety, all-solid-state batteries that do not use liquid in the electrolyte layer but use solid electrolytes are being actively researched. These lithium-ion secondary batteries are widely used as power sources for mobile phones and small devices, and are also being considered as potential power sources for electric vehicles. However, their energy density is lower than that of gasoline-powered vehicles, and a higher energy density is required to achieve the same driving range. However, improvements to the carbon anodes used in commercially available lithium-ion secondary batteries have reached their limits, and anode materials with higher capacity are needed. However, new anode materials using materials other than carbon are prone to lithium dendritic deposition at the anode during charging, and the deposited metal can break through the separator, causing an internal short circuit between the positive and negative electrodes and a risk of fire.

[0003] Various attempts have been made to obtain new negative electrode materials that solve this problem, and several reports have been published. For example, a negative electrode material that mixes scaly fine powder of Si with carbon has been disclosed (Patent Document 1). Another example has been disclosed: a negative electrode for a nonaqueous secondary battery that has an active material layer of an intermetallic compound capable of absorbing and desorbing Li on a current collector of Cu or a Cu alloy (Patent Document 2). Yet another example has been disclosed: a negative electrode that has a total of three or more layers stacked alternately, each layer containing a metal that does not alloy with Li and a metal element or compound of a metal element that can alloy with Li (Patent Document 3). These examples are attempts to obtain new anode materials without using Li-based metals as the anode. On the other hand, Li-based metal anodes have a large theoretical capacity (3861 mAh g -1 ) and the most noble redox potential (-3.045 V vs. SHE), making it the most attractive material for achieving high energy density. By using a Li-based metal anode, it is possible to construct a battery with high energy density. Attempts to use a Li-based metal anode as the anode have been made, for example, by using a lithium metal compound on the surface of pyrolytic graphite oxide (Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-032447 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-319457 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-103476 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-008653 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even when a Li-based metal is used as the anode, as described in Patent Document 4, for example, dendritic precipitation of alkali metals occurs, inducing an internal short circuit. In all-solid-state batteries, dendritic precipitation of alkali metals also induces an internal short circuit, causing a significant deterioration in battery performance. For this reason, the practical application of anodes using Li-based metals has not progressed. An object of the present invention is to provide a novel anode material that uses a Li-based metal and is superior in that it can suppress dendritic precipitation of alkali metals. [Means for solving the problem]

[0006] As a result of intensive investigations, the inventors of the present invention have found that the above-mentioned problems can be solved by an anode composite including an anode active material containing, as main components, Li and an element M that can form a solid solution with Li, and a substance X that has a higher oxidation-reduction potential than the anode active material or has no electrode activity, and have arrived at the present invention. Thus, according to the present invention, there is provided an anode composite comprising an anode active material containing, as main components, Li and an element M that is solid-soluble in Li, and a substance X that has a higher oxidation-reduction potential than the anode active material or has no electrode activity. The present invention also provides an anode composite including an anode layer containing an anode active material containing Li and Mg as main components. Furthermore, according to the present invention, there is provided a secondary battery comprising the above-mentioned negative electrode composite, an electrolyte layer in contact with the thin layer, and a positive electrode composite containing a positive electrode active material. [Effects of the Invention]

[0007] According to the present invention, a novel negative electrode composite having excellent dissolution and deposition characteristics can be provided. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1 is a schematic diagram of a symmetric cell 1. [Figure 1B] FIG. 2 is a schematic diagram of a symmetric cell 2. [Figure 1C] FIG. 1 is a schematic diagram of a symmetric cell 3. [Figure 2] 1 shows the results of constant current cycle tests on symmetric cell 1 and symmetric cell 3. [Figure 3] 1 shows the results of constant current cycle tests on symmetrical cells 2 and 3. [Figure 4] 1 is an SEM image of the fracture surface of symmetric cell 1 after short circuiting. [Figure 5] 1 is an SEM image of the fracture surface of symmetric cell 2 after short circuiting. [Figure 6] 10 is an SEM image of the fracture surface of symmetric cell 3 after short circuiting. [Figure 7] FIG. 1 is a schematic diagram of a symmetric cell 4. [Figure 8] 1 shows the results of a constant current cycle test on symmetric cell 4. [Figure 9] 10 is an SEM image of the fracture surface of symmetric cell 4 after short circuiting. [Figure 10] 1 shows the results of XRD measurement of the interface of symmetric cell 1 after short circuiting. [Figure 11] 1 shows the results of XRD measurement of the interface of symmetric cell 2 after short circuiting. [Figure 12] 1 shows the results of XRD measurement of the interface of symmetric cell 4 after short circuiting. [Figure 13A] 1 is an SEM image of the interface of symmetric cell 1 after short circuiting. [Figure 13B] 10 is an SEM-EDS image of the Mg at the interface of symmetric cell 1 after short circuiting. [Figure 14A] 10 is an SEM image of the interface of symmetric cell 2 after short circuiting. [Figure 14B] 10 is an SEM-EDS image of Sn at the interface of symmetric cell 2 after short circuit. [Figure 15A] 10 is an SEM image of the interface of symmetric cell 4 after short circuiting. [Figure 15B] 10 is an SEM-EDS image of Sn at the interface of symmetric cell 4 after short circuit. [Figure 16] 1 shows the results of constant current cycle tests on symmetrical cells 2, 5, and 6. [Figure 17] 1 shows the results of a constant current cycle test on symmetric cell 7. [Figure 18]1 shows the results of XRD measurement of the interface of symmetric cell 7 after short circuiting. [Figure 19] 10 is an SEM image of the interface of symmetric cell 7 after short circuiting. [Figure 20A] 10 is an SEM-EDS image of Sn at the interface of symmetric cell 7 after short circuit. [Figure 20B] 10 is an SEM-EDS image of the interface of symmetric cell 7 after short circuiting for I. [Figure 21A] This shows the results of a constant current cycle test of symmetric cell 3 at room temperature. [Figure 21B] This shows the results of a constant current cycle test at room temperature for symmetric cell 4. [Figure 22] 1 shows the results of XRD measurements of the interfaces of symmetric cell 3 and symmetric cell 4 after constant current cycle testing at room temperature. [Figure 23] 10 is an SEM image of the interface of symmetric cell 4 after constant current cycling at room temperature. DETAILED DESCRIPTION OF THE INVENTION

[0009] (negative electrode composite) The negative electrode composite of the present invention includes (1) a negative electrode active material containing, as main components, Li and an element M that is solid-soluble in Li, and (2) a substance X that has a higher oxidation-reduction potential than the negative electrode active material or does not have electrode activity. Here, "contained as a main component" means that the total molar content of Li and element M, which is solid-soluble in Li, in the negative electrode active material is 50% or more with respect to all components constituting the negative electrode active material. The total molar content is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, more preferably 97% or more, more preferably 98% or more, more preferably 99% or more, and most preferably 100%.

[0010] The element M (hereinafter simply referred to as element M) that is solid-soluble in Li is not particularly limited as long as it is an element that is solid-soluble in Li. Here, a solid solution refers to an element in which two or more elements are dissolved together to form a homogeneous solid state. Furthermore, being solid-soluble in Li essentially means that it is solid-soluble in Li with a body-centered cubic structure or in a metastable phase of Li. The negative electrode active material preferably contains a solid solution of Li and element M as a main component, and more preferably a solid solution of Li and element M. Note that solid solution refers to a state in which the solid solution is substantially solid. Here, substantially solid solution refers not only to a state in which Li and element M are completely solid-solved, but also to a state in which unreacted Li and element M are finely dispersed in the solid solution of Li and element M. The finely dispersed unreacted Li and element M often do not have a particularly adverse effect on performance, but is preferably 5 parts by volume or less, more preferably 4 parts by volume or less, more preferably 3 parts by volume or less, more preferably 2 parts by volume or less, more preferably 1 part by volume or less, more preferably 0.5 parts by volume or less, and more preferably 0.1 parts by volume or less, relative to 100 parts by volume of the solid solution.

[0011] The element M may be one element or multiple elements, but is preferably Mg 、Z n, Au, Ag, Pt, N a or It is preferable that the element M is at least one element selected from the following: Furthermore, it is more preferable that the element M contains at least Mg, and it is even more preferable that the element M contains Mg as the main component. In the negative electrode active material, the molar ratio of Li to element M is not particularly limited, but for example, the molar ratio of Li to element M is preferably Li:element M=0.999:0.001-0.300:0.700, more preferably 0.999:0.001-0.400:0.600, more preferably 0.999:0.001-0.500:0.500, and more preferably 0.999:0.001-0.700:0.300. More specifically, when element M is Mg, the molar ratio of Li to Mg is preferably Li:Mg=0.999:0.001-0.300:0.700, more preferably 0.999:0.001-0.700:0.300. . Former When element M is Zn, the molar ratio of Li to Zn is preferably Li:Zn=0.999:0.001-0.700:0.300, and more preferably 0.999:0.001-0.900:0.100. When element M is Au, the molar ratio of Li to Au is preferably Li:Au=0.999:0.001-0.700:0.300, and more preferably 0.999:0.001-0.900:0.100. When element M is Ag, the molar ratio of Li to Ag is preferably Li:Ag=0.999:0.001-0.700:0.300, and more preferably 0.999:0.001-0.900:0.100. When the element M is Pt, the molar ratio of Li to Pt is preferably Li:Pt=0.999:0.001-0.700:0.300, more preferably 0.999:0.001-0.900:0.100. When the element M is Na, the molar ratio of Li to Na is preferably Li:Na=0.999:0.001-0.700:0.300, more preferably 0.999:0.001-0.900:0.100. .child By including these substances in the negative electrode active material at these molar ratios, it is possible to provide a negative electrode composite having excellent dissolution and deposition characteristics.

[0012] The negative electrode active material can be produced by combining a raw material containing Li and an element M capable of forming a solid solution in Li, and at least partially reacting the two. Examples of the raw material containing Li and an element M capable of forming a solid solution in Li include Li, Mg , Z n, Au, Ag, Pt, or N a The raw material may be a metal element, or a sulfide or oxide of element M. As a sulfide containing element M, one that reacts with Li to form lithium sulfide and a lithium alloy is more preferable. As an oxide containing element M, one that reacts with Li to form lithium oxide and a lithium alloy is more preferable. Among these, a metal element is more preferable as the raw material. Examples of methods for producing a negative electrode active material include a method of mixing element M with Li, a method of bonding element M with lithium, and a method of allowing element M to coexist during the production of metallic Li. Methods for mixing element M with Li include a method of mixing element M with molten Li and a method of mechanochemically treating Li and element M. A ball mill can be used as a treatment device for mechanochemical treatment. A ball mill is preferred because it can generate large mechanical energy. Among ball mills, a planetary ball mill is preferred because it can efficiently generate high impact energy by rotating the pot on its axis and revolving the base in the direction opposite to the rotation. The treatment conditions can be appropriately set depending on the treatment equipment used. For example, when a planetary ball mill is used, the conditions include a rotation speed of 160 to 400 rpm and a treatment time of 0.1 to 120 hours. To prevent the raw material lithium salt from reacting with water or oxygen, the treatment is preferably carried out in an inert atmosphere (e.g., an argon atmosphere) using a glove box or the like, in an environment with a water concentration of 1000 ppm or less and an oxygen concentration of 1000 ppm or less.

[0013] The substance X is a substance that has a higher redox potential than the negative electrode active material or does not have electrode activity. The substance X is not particularly limited as long as it satisfies the above conditions. However, the substance X should preferably have a resistance per unit area of ​​100 Ωcm or more. 2 Preferably, it is 10 Ωcm or less. 2More preferably, it is 3 Ωcm or less. 2 It is more preferable that the value is 10 or less. -8 S cm -1 It is preferable that the ionic conductivity is equal to or higher than this.

[0014] As the substance X, any metal that has a small amount of solid solubility in Li (e.g., Al, Zn, Au, Ag, Na, In, Bi) can function as the substance X, but it is more preferable to use a metal or semimetal that can be alloyed with Li but is not solid-soluble in Li, and / or an alloy of such a metal or semimetal with Li. Examples of the metal include Sn, Ni, and Fe, and examples of semimetals include Si. Examples of alloys of Li with a metal that is not solid-soluble in Li include Li4Sn, Li4Sn, and Li4Sn. 22 Sn5, Li 4.4 Examples include Si, etc. It is preferable to use at least one selected from these, and it is more preferable to select at least Sn. It is preferable that substance X covers the negative electrode active material, and in batteries using a solid electrolyte, it is more preferable that substance X be present between the negative electrode active material and the solid electrolyte. By having substance X cover the negative electrode active material or be present between the negative electrode active material and the solid electrolyte, a negative electrode composite with excellent dissolution and deposition characteristics can be provided. It is also more preferable that substance X cover the entire interface between the negative electrode active material and the solid electrolyte. The thickness of the coating substance X is not particularly limited, but can be set, for example, in the range of 5 to 1000 nm, preferably in the range of 50 to 1000 nm, more preferably in the range of 50 to 500 nm, more preferably in the range of 100 to 500 nm, and even more preferably in the range of 200 to 500 nm. The thickness of the coating substance X may be uniform or may have some deviation, but is preferably uniform. The degree of coverage is preferably 50% or more of the surface of the negative electrode active material, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 99% or more, and most preferably 100%. Furthermore, substance X is present in 50% or more of the interface between the negative electrode active material and the solid electrolyte, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 99% or more, and most preferably 100%.

[0015] Alternatively, the substance X may be laminated on a negative electrode layer containing the negative electrode active material. By laminating the substance X on the negative electrode, reductive decomposition of the solid electrolyte layer can be reduced, and performance degradation can be suppressed. Therefore, the anode composite of the present invention may include an anode layer containing an anode active material containing, as a main component, Li and an element M that can form a solid solution in Li, and a thin layer laminated on the anode layer and containing, as a main component, a substance X. By providing the thin layer on the anode layer, it is possible to provide an anode composite with more excellent dissolution and deposition properties. "Containing as a major component" as used herein means that the molar content of substance X in the thin layer is 50% or more of all components constituting the thin layer, preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, more preferably 97% or more, more preferably 98% or more, more preferably 99% or more, and most preferably 100%. The form of the negative electrode layer is not particularly limited, but it is preferably a layer containing a solid solution of Li and element M as a main component, and more preferably a layer of the solid solution. The shape of the negative electrode layer is not particularly limited as long as it can function as a negative electrode composite, and can take various shapes such as a cylindrical shape, an elliptical cylindrical shape, a rod shape, a foil shape, a film shape, etc. The thickness of the negative electrode layer is not particularly limited, but for example, when the negative electrode layer is in the form of a membrane or a film, the thickness can be set, for example, in the range of 5 to 2000 nm, preferably in the range of 5 to 1000 nm, more preferably in the range of 50 to 1000 nm, and even more preferably in the range of 50 to 500 nm.

[0016] The negative electrode composite (particularly, the negative electrode layer) may contain a binder, a conductive material, a solid electrolyte, etc. Furthermore, it may contain a negative electrode active material different from the negative electrode active material containing Li and an element M capable of forming a solid solution with Li as the main components. Examples of the negative electrode active material include carbon-based materials such as natural graphite, artificial graphite, acetylene black, ketjen black, denka black, carbon black, and VGCF; metals such as Si, Li alloys, Na alloys, Au, Pt, Pd, Ag, Al, Bi, Sn, Sb, Zn, Mg, K, Ca, and Na; and Li. 4 / 3 Ti 5 / 3 Examples of the negative electrode active material include various transition metal oxides such as O4, Li3V2(PO4)3, and SnO. These negative electrode active materials may be used alone or in combination of two or more. The negative electrode active material can be contained in an amount of 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, more preferably 10 parts by weight or less, more preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and more preferably 1 part by weight or less, relative to 100 parts by weight of the total amount of Li and element M in the negative electrode composite.

[0017] The binder is not particularly limited, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, polyethylene, styrene butadiene rubber, acrylonitrile butadiene rubber, and copolymers thereof. When mixing the binder and the negative electrode active material of the present invention using a solvent, the solvent is not particularly limited, but it is preferable that the solvent does not cause a side reaction with the negative electrode active material of the present invention. The binder can be contained in an amount of 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, more preferably 10 parts by weight or less, more preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and more preferably 1 part by weight or less, relative to 100 parts by weight of the total amount of Li and element M in the negative electrode composite.

[0018] The conductive material is not particularly limited, and examples thereof include natural graphite, artificial graphite, acetylene black, ketjen black, denka black, carbon black, vapor grown carbon fiber (VGCF), and the like. The conductive material can be contained in an amount of 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, more preferably 10 parts by weight or less, more preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and more preferably 1 part by weight or less, relative to 100 parts by weight of the total amount of Li and element M in the negative electrode composite.

[0019] The solid electrolyte contained in the negative electrode composite is not particularly limited, and the solid electrolyte used in the production of a secondary battery described below can be used. The solid electrolyte can be contained in an amount of 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 20 parts by weight or less, more preferably 10 parts by weight or less, more preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and more preferably 1 part by weight or less, relative to 100 parts by weight of the total amount of Li and element M in the negative electrode composite.

[0020] The thickness of the thin layer is not particularly limited, but is preferably in the range of 5 to 500 nm, more preferably in the range of 50 to 500 nm, more preferably in the range of 100 to 500 nm, and even more preferably in the range of 200 to 500 nm. By having the thin layer have a thickness in the range of 5 to 500 nm, it is possible to provide a negative electrode composite with more excellent dissolution and deposition characteristics. Furthermore, it is preferable that the thin layer has a uniform thickness.

[0021] The method for laminating a thin layer on the negative electrode layer is not particularly limited as long as it can form a thin layer on the negative electrode layer. For example, gas phase methods such as PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition), liquid phase methods such as electroplating and coating, or solid phase methods such as LB (Langmuir-Blodgett) can be used. Examples of PVD methods include vacuum deposition and sputtering, and sputtering is particularly preferred from the perspective of mass production. The surface of the negative electrode layer may be polished before forming the thin layer to reduce the unevenness of the negative electrode layer surface.

[0022] The present invention also provides a negative electrode composite including a negative electrode layer containing a negative electrode active material containing Li and Mg as main components. "Containing as a main component" as used herein means that the total molar content of Li and Mg in the negative electrode active material is 50% or more relative to all components constituting the negative electrode active material. The molar content is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, more preferably 97% or more, more preferably 98% or more, more preferably 99% or more, and most preferably 100%. The description of the negative electrode layer is the same as above. The negative electrode active material preferably contains a solid solution of Li and Mg as a main component, and more preferably the negative electrode active material is a solid solution of Li and Mg. The negative electrode layer is more preferably a layer of a solid solution of Li and Mg, and the molar ratio of Li to Mg is more preferably Li:Mg=0.999:0.001-0.300:0.700, and more preferably 0.999:0.001-0.700:0.300. Here, the meanings of "containing a solid solution as a main component" and "solid solution" are as described above.

[0023] The present invention also provides a negative electrode composite comprising: a negative electrode layer containing a negative electrode active material; and a thin layer laminated on the negative electrode layer and containing Sn and / or an alloy of Sn and Li as a main component. "Containing as a main component" as used herein means that the molar content of Sn and / or an alloy of Sn and Li is 50% or more of all components constituting the thin layer, and the molar content is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, more preferably 95% or more, more preferably 97% or more, more preferably 98% or more, more preferably 99% or more, and most preferably 100%. The description of the thin layer is the same as that described above. In addition, the Sn and / or Sn-Li alloy has a resistivity of 10 Ωcm 2 It is preferable that the thin layer has a thickness in the range of 100 to 500 nm, and more preferably in the range of 200 to 500 nm.2 By exhibiting the following resistance, it is possible to provide a negative electrode composite having better dissolution and deposition properties.

[0024] The negative electrode composite may consist solely of a negative electrode active material containing Li and element M as main components, or may be mixed with the above-mentioned binder, conductive material, negative electrode active material, or a solid electrolyte used in producing a secondary battery described below.

[0025] The negative electrode composite of the present invention may further be combined with a current collector. The current collector is not particularly limited in material, shape, etc., as long as it can be combined with the negative electrode composite of the present invention and functions as a current collector. The shape of the current collector may be a uniform alloy plate or a shape with holes. It may also be in the form of a foil, sheet, or film.

[0026] Examples of materials for the current collector include Ni, Cu, Ti, Fe, Co, Ge, Cr, Mo, W, Ru, Pd, stainless steel, and steel. In addition to the above materials, the current collector may be coated with either gold or aluminum. The thickness of the coating is not particularly limited, but is preferably 10 nm to 100 μm. Furthermore, it is preferable that the coating have a uniform thickness. The coating method is not particularly limited as long as it can coat the current collector, but for example, it can be formed by vapor deposition on the surface using a sputter coater. The negative electrode composite of the present invention may be formed directly on the current collector.

[0027] (Method of manufacturing negative electrode composite) The method for producing the anode composite is not particularly limited as long as it can combine the anode active material produced by the above-described production method with a raw material containing a substance X that has a higher oxidation-reduction potential than the anode active material or does not have electrode activity. The anode composite may further be combined with any of a binder, a conductive material, an electrolyte, and the like. When the anode composite has a thin layer, a binder, a conductive material, an electrolyte, and the like are optionally mixed with the anode active material, and the obtained mixture is pressed to obtain a pellet-shaped anode layer, which is then laminated on the anode layer to form a thin layer, thereby producing the anode composite.

[0028] Although the battery using these anode composites is not particularly limited, it is preferably used in a secondary battery, more preferably an all-solid-state secondary battery. The anode composite of the present invention has excellent dissolution and deposition properties and can therefore be suitably used as the anode of an all-solid-state secondary battery.

[0029] (Secondary battery) The present invention provides a secondary battery comprising the anode composite of the present invention, an electrolyte layer in contact with the thin layer, and a cathode composite containing a cathode active material. The present invention also provides a secondary battery comprising the negative electrode composite of the present invention, an electrolyte layer, and a positive electrode composite containing a positive electrode active material. The secondary battery may be a general lithium secondary battery or an all-solid-state secondary battery. The configuration of the secondary battery will be described below.

[0030] (Positive electrode composite) The positive electrode composite includes a positive electrode active material. The positive electrode composite is not particularly limited as long as it can be used as a secondary battery in combination with the negative electrode composite of the present invention, and may be configured by combining positive electrode active materials. The positive electrode active material preferably has a high redox potential, and more preferably has an average charge / discharge potential of 3.5 V or more relative to the redox potential of Li. The positive electrode composite may consist of only the positive electrode active material, or may be mixed with a binder, a conductive material, an electrolyte, etc. The positive electrode active material is, for example, Li4Ti5O 12 , LiCoO2, LiMnO2, LiVO2, LiCrO2, LiNiO2, Li2NiMn3O8, Li(Ni , Co Mn ,)O2, FeS2, TiS2, LiFeO2, Li3V2(PO4)3, LiMn2O4, Li2MnO3-Li(Ni , Co , Mn , )O2, Li7CuS 4、 Li5CuS3, Li3CuS2, MoS x (x≧2), S, Li2S, TiS x , V2O5, etc.

[0031] The positive electrode composite can be obtained in the form of a pellet by, for example, mixing a positive electrode active material and, optionally, a binder, a conductive material, an electrolyte, etc., and pressing the resulting mixture.

[0032] The positive electrode composite may further include a current collector, which is the same as that described above for the negative electrode composite.

[0033] The electrolyte layers used in secondary batteries can be roughly divided into two types: those that are mainly composed of an electrolytic solution and those that are composed of a solid electrolyte.

[0034] (1) Non-aqueous electrolyte layer The non-aqueous electrolyte layer used in the present invention can be composed of a mixture of an electrolyte and a non-aqueous solvent. Examples of electrolytes include LiClO4, LiPF6, LiBF4, LiCF3SO3, LiAsF6, LiB(C6H5)4, LiCl, LiBr, CH3SO3Li, CF3SO3Li, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO3CF3)2. The non-aqueous solvent is not particularly limited, and examples thereof include carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, amines, esters, amides, and phosphate ester compounds. Representative examples of these include 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate, vinylene carbonate, methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate, 1,4-dioxane, 4-methyl-2-pentanone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, trimethyl phosphate, triethyl phosphate, etc. These may be used alone or in combination of two or more. (2) Solid electrolyte layer The solid electrolyte constituting the solid electrolyte layer is not particularly limited, and may be any solid electrolyte used in all-solid-state secondary batteries, such as a sulfide-based solid electrolyte or an oxide-based solid electrolyte. Examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiI-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-GeS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, Li 10 GeP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li7P3S 11 , Li3PS4, Li 6-yPS 5-x β 1+y (β=Cl or Br) or Li 3.25 P 0.75 S4, etc. These sulfide-based solid electrolytes may be used alone or in combination of two or more. Examples of oxide-based solid electrolyte materials include Li2O-B2O3-P2O3, Li2O-SiO2, Li2O-P2O5, and Li5La3Ta2O. 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4 or Li3BO3-Li2SO4-Li2CO3, etc. These oxide-based solid electrolytes may be used alone or in combination of two or more. Among these, the solid electrolyte is preferably a sulfide-based solid electrolyte.

[0035] In addition to the solid electrolyte material, the solid electrolyte layer may contain other components used in all-solid-state secondary batteries, such as metal oxides of P, As, Ti, Fe, Zn, or Bi, and binders such as polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polymethyl methacrylate, or polyethylene. The solid electrolyte may be in a glassy state or a glass-ceramic state. The term "glassy" refers to a substantially amorphous state. Here, "substantially" includes not only a 100% amorphous state but also a state in which a crystalline solid electrolyte is finely dispersed. The term "glass-ceramic state" refers to a state that occurs when a glassy solid electrolyte is heated to a temperature equal to or higher than the glass transition point. The glass-ceramic solid electrolyte may have crystalline portions dispersed in an amorphous glass component. The proportion of the crystalline portions can be measured by observation using a transmission electron microscope or crystal structure analysis using the Rietveld method. Furthermore, the glass-ceramic solid electrolyte may not have the glass transition point that the corresponding glass-like solid electrolyte has.

[0036] The solid electrolyte can be formed into a solid electrolyte layer by, for example, pressing it to a predetermined thickness. The pressing pressure may be selected from the range of 50 to 2000 MPa.

[0037] The method for producing the solid electrolyte layer is not particularly limited as long as it is a method that allows mixing of the solid electrolyte material. The solid electrolyte material may be any of the above-described solid electrolyte materials.

[0038] In the secondary battery of the present invention, when the negative electrode composite does not have a thin layer or is not coated with substance X, it is preferable to provide a buffer layer between the negative electrode composite and the electrolyte layer. When the buffer layer is formed by coating either the anode composite or the electrolyte layer, it may cover the entire surface where the anode composite and the electrolyte layer contact, or may cover only a portion of the surface. The degree of coverage is preferably 20% or more of the surface of the anode composite, more preferably 30% or more, more preferably 40% or more, more preferably 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, preferably 90% or more, more preferably 99% or more, and most preferably 100%. The material for the buffer layer is not particularly limited as long as it does not adversely affect the effects of the negative electrode composite of the present invention, and examples thereof include conductive polymers and metal materials. Examples of conductive polymers include polyethylene oxide, polypropylene oxide, polythiophene, and polyaniline. Examples of inorganic materials include alumina, AlF3, Cu, Ni, Co, Ti, Fe, Cr, Mo, W, Pd, and Pt. The conductive polymers and metal materials may be used alone or in combination with multiple materials. In addition to the above materials, binders, conductive materials, electrolytes, negative electrode active materials, and the like may be further mixed. The thickness of the buffer layer is not particularly limited, but can be set appropriately between 10 nm and 100 μm.

[0039] (Secondary battery manufacturing method) The present invention also provides a method for producing a secondary battery using the negative electrode composite of the present invention.

[0040] (I) Lithium secondary batteries When producing a lithium secondary battery using an electrolytic solution, for example, a laminate of the negative electrode composite of the present invention, a separator, and the above-described positive electrode composite for a lithium secondary battery is inserted into a battery can, and a mixture of the electrolyte and a non-aqueous solvent is poured into the battery can, thereby obtaining a lithium secondary battery. The separator is preferably a microporous polymer film. Specifically, a separator made of nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polyolefin polymer such as polybutene can be used. The positive electrode, separator, and negative electrode may be stacked or wound. (II) All-solid-state battery An all-solid-state battery can be obtained, for example, by laminating a current collector, the anode composite of the present invention, a solid electrolyte layer, the above-described cathode composite, and a current collector, pressing the laminate, and then fixing the laminate in a container to obtain a cell. When the negative electrode composite does not have a thin layer, the above-mentioned buffer layer may be provided between the negative electrode composite and the solid electrolyte layer. [Example]

[0041] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by these examples. In the following examples and comparative examples, Li2S manufactured by Mitsuwa Chemical Co., Ltd., LiI and P2S5 manufactured by Aldrich, Sn manufactured by Nilaco Corporation, Zn manufactured by Nilaco Corporation, and Li foil manufactured by Furuuchi Chemical Co., Ltd. were used. Furthermore, Au was used that had been recast by FDK Factory. In the following examples and comparative examples, a Fritsch planetary ball mill, PULVERISETTE 5 (P-5), was used for mechanochemical processing. A Sanyu Electronics QUICK COATER SC-701MkII ADVANCED was used for sputtering. An NPA System NPa-6003 was used for cold isostatic pressing (CIP). A Nagano BTS-2004 was used for constant current cycle testing. A Rigaku SmartLab fully automated multipurpose X-ray diffractometer was used for X-ray diffraction. A Hitachi High-Technologies field emission scanning electron microscope (FE-SEM, SU8200) was used for scanning electron microscope (SEM), and an Horiba EMAXEvolution X-Max was used for energy dispersive X-ray analysis (EDS).

[0042] (Preparation of Symmetric Cells with Li-Mg Negative Electrode Active Material) Example 1 A symmetric cell 1 having a Li—Mg negative electrode active material was fabricated by the following procedure. The following cell fabrication was carried out in a glove box in an Ar atmosphere.

[0043] Preparation of electrolyte pellets (I: Preparation of Li3PS4 glass solid electrolyte powder) The LPS solid electrolyte pellets for the control cell used in this experiment were prepared as follows. Li2S and P2S5 were placed in a zirconia pot (250 mL) in a ratio of 75:25 together with zirconia balls (4 mm diameter, 250 g), and mechanochemically treated using the planetary ball mill P-5 to produce Li3PS4 glass solid electrolyte powder (LPS powder). The mechanochemical treatment conditions were a table rotation speed of 210 rpm and a treatment time of 70 hours. (II: Preparation of LPS pellets) 150 mg of the LPS powder prepared in step I above was pressed into a cylindrical cemented carbide die with a 10 mm diameter hole using two cemented carbide rods at a pressure of 360 MPa for 5 minutes to produce an LPS pellet.

[0044] (III: Preparation of Li-Mg electrode foil) Honjo Metals Co., Ltd., 250 μm thick Li 0.93 Mg 0.07 Foil was used.

[0045] (IV: Preparation of symmetrical cells) The Li prepared in step III above was applied to both sides of the LPS pellet prepared in step II above. 0.93 Mg 0.07 A 9.0 mm diameter foil was attached to the cell. On both sides of this, 20 μm thick 10.0 mm diameter SUS foil was attached. This was then vacuum sealed in a 150 μm thick aluminum laminate film (50 μm of which was aluminum vapor deposition). This was then cold isostatically pressed (CIP) at 80 MPa for 2 minutes to produce Symmetric Cell 1. A schematic diagram of the resulting Symmetric Cell 1 is shown in Figure 1A.

[0046] (Fabrication of a symmetric cell with a Sn thin film) Example 2 A symmetric cell with a Sn thin film was fabricated using the same LPS pellets as those fabricated in step II above.

[0047] (V: Thin film deposition) A thin Sn film was formed on both sides of the LPS pellet prepared in step II above. Sputtering was performed for 6 minutes using Ar as the sputtering gas at a sputtering power of approximately 6.5 W, resulting in a Sn thin film thickness of 200 nm.

[0048] The thin film formed in step V above was applied to both sides of the LPS pellet. 0.93 Mg 0.07 Symmetric cell 2 was fabricated in the same manner as in step IV, except that a 250 μm thick Li foil was attached instead of the foil. A schematic diagram of the fabricated symmetric cell 2 is shown in Figure 1B.

[0049] Comparative Example 1 As a comparative example, the LPS pellet prepared in step II above was coated with Li on both sides. 0.93 Mg 0.07 Symmetric cell 3 was fabricated in the same manner as in step IV, except that a Li foil with a thickness of 250 μm was attached instead of the Li foil. A schematic diagram of the fabricated symmetric cell 3 is shown in Figure 1C.

[0050] (Constant current cycle test) A constant current cycle test was carried out using the symmetric cells 1 to 3 produced in Examples 1 and 2 or Comparative Example 1. The cycle test was carried out at a test temperature of 100°C, with a cell restraining pressure of 1 MPa, and with one cycle consisting of one hour of charge and discharge, and the current was increased by 0.2 mA every five cycles from 0.2 mA.

[0051] The results of constant current cycle tests performed on symmetric cells 1 to 3 are shown in Figures 2 and 3. Figure 2 shows the results for symmetric cells 1 and 3, and Figure 3 shows the results for symmetric cells 2 and 3. Figures 2 and 3 show that symmetric cells 1 and 2 did not short-circuit even at current densities higher than the current density at which symmetric cell 3 short-circuited (the arrows in Figures 2 and 3). This indicates that symmetric cells 1 and 2, which used the negative electrode composite of the present invention, had improved dissolution and deposition characteristics.

[0052] After the constant current cycle test, the interface between the solid electrolyte and the negative electrode of the symmetric cells 1 to 3 was observed with an SEM after short circuiting. To measure the interface, the symmetric cells were broken perpendicular to the stacking plane, and the broken surface was observed.

[0053] The results of SEM observations are shown in Figures 4 to 6. Figure 4 shows a cross-section of symmetric cell 1 after a short circuit, Figure 5 shows a cross-section of symmetric cell 2 after a short circuit, and Figure 6 shows symmetric cell 3 after a short circuit. Figures 4 and 6 show that a reaction layer has formed at the Li / Li3PS4 interface due to the reductive decomposition of Li3PS4. In contrast, Figure 5 shows no reaction layer, and the formation of a reaction layer is suppressed by the Sn thin film. This is presumably because Sn does not dissolve in Li, so it does not diffuse into the Li in the negative electrode, and the layer shape is maintained.

[0054] (Fabrication of a symmetric cell having a Li-Mg negative electrode active material and a Sn thin film) Example 3 A thin Sn film was formed on both sides of the LPS pellet prepared in step II above. Sputtering was carried out in the same manner as above for 6 minutes, and the thickness of the thin Sn film was set to 200 nm. Li 0.93 Mg 0.07 A foil of 10.0 mm diameter was attached. Further, 20 μm thick SUS foils with a diameter of 10.0 mm were attached to both sides of this. This was then vacuum sealed in an aluminum laminate film. After that, cold isostatic pressing (CIP) was performed under the same conditions as above to produce symmetric cell 4. A schematic diagram of the produced symmetric cell 4 is shown in Figure 7.

[0055] The same constant current cycle test was carried out on the fabricated symmetric cell 4. The results are shown in Figure 8. As shown in Figure 8, symmetric cell 4 did not short circuit even at a current density higher than that of symmetric cell 1. This demonstrates that symmetric cell 4 has particularly excellent dissolution and deposition properties.

[0056] For control cell 4 after the constant current cycle test, the interface between the solid electrolyte and the negative electrode after short circuiting was observed using an SEM. The results of the SEM observation are shown in Figure 9. Figure 9 shows that there is no reaction layer in control cell 4, indicating that even when a Li-Mg negative electrode active material is used, the formation of a reaction layer is suppressed by the Sn thin film.

[0057] (XRD measurement of symmetric cell) X-ray diffraction (XRD) measurements were performed to analyze the structure of the interface between the solid electrolyte and the negative electrode of the short-circuited symmetric cells 1, 2, and 4 after the constant current cycle test described above. A SmartLab was used as the X-ray diffractometer, and CuKα radiation (= 1.54056 × 10 -10 m), the tube voltage was 45 kV, the tube current was 200 mA, the scan angle 2θ = 10° to 60°, the sampling interval was 0.02°, and the scan speed was 10° min -1 The structure was analyzed in a symmetric cell. Because the fabricated symmetric cell was unstable in the atmosphere, the process of attaching the sample to the non-reflective sample plate and sealing the sample in the airtight sample stage was all carried out in a glove box under an argon atmosphere. Measurements were carried out after removing the SUS foil from the short-circuited symmetric cell.

[0058] The results of the XRD measurements are shown in Figures 10 to 12. Figure 10 shows the measurement results for symmetric cell 1, Figure 11 shows the measurement results for symmetric cell 2, and Figure 12 shows the measurement results for measurement cell 4. For comparison, the figures also show the results for Li 22 The results of measuring Sn5, Li, and Li2S are also described. Figure 10 shows that a peak of Li2S, a reduction product of Li, is observed at the interface of symmetric cell 1. Figure 11 shows that a peak of Li2S, the most Li-rich alloy phase, is observed at the interface of symmetric cell 2. 22 As shown in Figure 12, the Sn5 peak was observed at the interface of symmetric cell 4. 22 A peak of Sn5 was observed, indicating that even when a Li-Mg negative electrode active material was used, the Sn thin film suppressed the production of the reduction product Li2S.

[0059] (SEM-EDS measurement of symmetric cell) The interfaces between the solid electrolyte and the negative electrode of the short-circuited symmetric cells 1, 2, and 4 after the constant current cycle test were subjected to SEM-EDS. The measurements were carried out at an accelerating voltage of 8 kV. The measurement results for symmetric cell 1 are shown in Figures 13A and 13B, those for symmetric cell 2 in Figures 14A and 14B, and those for symmetric cell 3 in Figures 15A and 15B. Figure 13B shows that Mg is not present in the reaction layer. Figures 14B and 15B show that Sn remains as a film even after the short circuit.

[0060] (Example of changing the thickness of the Sn thin film) Example 4 A symmetric cell 5 was fabricated in the same manner as in Example 2, except that sputtering was carried out for 1 minute and the thickness of the Sn thin film was set to 60 nm.

[0061] Example 5 A symmetric cell 6 was fabricated in the same manner as in Example 2, except that sputtering was carried out for 3 minutes and the thickness of the Sn thin film was set to 100 nm.

[0062] The same constant current cycle test was carried out on the fabricated symmetric cells 5 and 6. The results are shown in Figure 16. Figure 16 shows the results of symmetric cells 5 and 6 together with the results of symmetric cell 2. Figure 16 shows that the dissolution and deposition characteristics improve by increasing the thickness of the film.

[0063] (Fabrication of symmetric cells with different solid electrolytes) Example 6 A symmetric cell was fabricated using pellets prepared using 54Li3PS4-46LiI as the solid electrolyte instead of the LPS pellets prepared in step II above.

[0064] (VI: Preparation of Li3PS4·LiI solid electrolyte powder) Li2S, P2S5, and LiI were placed in a zirconia pot (250 mL) in a ratio of Li2S:P2S5:LiI = 52.5:17.5:30, and treated in the same manner as in step I above to produce 54Li3PS4-46LiI solid electrolyte powder.

[0065] (VII: Preparation of Li3PSS4·LiI solid electrolyte pellets 54Li3PS4·46LiI pellets were prepared in the same manner as in step II above, except that the 54Li3PS4·46LiI powder prepared in step VI above was used instead of the LPS powder.

[0066] A symmetric cell 7 was fabricated in the same manner as in Example 3, except that the 54Li3PS4·46LiI pellets prepared in step VII above were used.

[0067] The same constant current cycle test was performed on the prepared symmetric cell 7. The results are shown in Figure 17. From Figure 17, it can be seen that the symmetric cell with a Li-Mg negative electrode active material and a Sn thin film has excellent dissolution and deposition properties, even when 54Li3PS4·46LiI is used as the solid electrolyte instead of LPS.

[0068] The results of XRD measurement of the symmetric cell 7 after the constant current cycle test are shown in Figure 18. The figure also includes a Li 22 The results of measuring Sn5 and Li are also shown. At the interface of the symmetric cell 7, Li 22 A peak of Sn5 was observed, indicating that, as in the control cell 4, the Sn thin film suppresses the production of the reduction product Li2S.

[0069] For symmetric cell 7 after the constant current cycle test, the interface between the solid electrolyte and the negative electrode after a short circuit was observed using SEM. The SEM observation results are shown in Figure 19. Measurement results using SEM-EDS are shown in Figures 20A and 20B, respectively. Figure 20A shows the results for Sn, and Figure 20B shows the results for I. As can be seen from Figure 19, no reaction layer was formed in symmetric cell 7, just like in symmetric cell 4. Figures 20A and 20B show that Sn remained as a film even after a short circuit.

[0070] (Evaluation of dissolution and deposition characteristics of symmetrical cells at room temperature) Using Symmetric Cell 4 and Symmetric Cell 3 (comparison), a constant current cycle test was conducted at room temperature to measure performance. The cycle test was conducted at a test temperature of 25°C, with the cell restraining pressure at 1 MPa, and the current was increased by 0.05 mA every 5 cycles, with one hour of charge and discharge.

[0071] The results of the constant current cycle test are shown in Figures 21A and 21B, respectively. Figure 21A shows the results for symmetric cell 3, and Figure 21B shows the measurement results for symmetric cell 4. Figures 21A and 21B show that symmetric cell 4, which has a Li-Mg negative electrode active material and a Sn thin film, has better dissolution and deposition properties than symmetric cell 3, even at room temperature.

[0072] The results of XRD measurements on symmetric cell 4 and symmetric cell 3 after the constant current cycle test are shown in Figure 22. The top graph in Figure 22 shows the results for symmetric cell 3, and the second graph from the top shows the results for symmetric cell 4. For comparison, the figure also shows the results for Li 22 The results of measuring Sn5 and Li are also shown. From Figure 22, the interface of symmetric cell 4 is Li 22 It was shown that the Sn5 peak was observed.

[0073] For control cell 4 after the constant current cycle test, the interface between the solid electrolyte and the negative electrode after a short circuit was observed using an SEM. The results of the SEM observation are shown in Figure 23. Figure 23 shows that the insertion of the Sn thin film suppresses the formation of a reaction layer. This shows that the interface is protected by the Sn thin film even during operation at room temperature.

Claims

1. A negative electrode layer containing a negative electrode active material; a thin layer containing substance X as a main component laminated on the negative electrode layer; Equipped with the negative electrode active material contains, as a main component, a solid solution in which an element M is dissolved in Li; The substance X has a higher redox potential than the negative electrode active material or has no electrode activity. the thin layer is disposed in contact with the electrolyte layer; The negative electrode composite, wherein the substance X is a metal or semimetal that can be alloyed with Li but is not solid-soluble in Li, and / or an alloy of the metal or semimetal with Li.

2. 2. The negative electrode composite according to claim 1, wherein the negative electrode active material is a solid solution of Li and the element M.

3. 2. The negative electrode composite according to claim 1, wherein the negative electrode layer is a layer of a solid solution of Li and the element M.

4. The negative electrode composite according to claim 1, wherein the molar ratio of Li to the element M is Li:element M=0.999:0.001-0.300:0.

700.

5. 5. The negative electrode composite according to claim 1, wherein the element M is at least one element selected from the group consisting of Mg, Zn, Au, Ag, Pt, and Na.

6. The substance X is 10 -8 S・cm -1 The negative electrode composite according to any one of claims 1 to 5, having the above ionic conductivity.

7. 2. The negative electrode composite according to claim 1, wherein the metal or semimetal is at least one selected from Sn, Ni, Fe, and Si.

8. 8. The negative electrode composite according to claim 1, wherein the thin layer has a thickness in the range of 5 to 500 nm.

9. The negative electrode composite according to any one of claims 1 to 8, wherein the element M is Mg.

10. 10. The negative electrode composite according to claim 1, wherein the substance X is Sn and / or an alloy of Sn and Li.

11. A negative electrode layer containing a negative electrode active material; a thin layer containing substance X as a main component laminated on the negative electrode layer; Equipped with the negative electrode active material contains, as a main component, a solid solution in which Mg is dissolved in Li; the thin layer is disposed in contact with the electrolyte layer; The negative electrode composite, wherein the substance X is a metal or semimetal that can be alloyed with Li but is not solid-soluble in Li, and / or an alloy of the metal or semimetal with Li.

12. The negative electrode composite according to claim 11 , wherein the negative electrode active material is a solid solution of Li and Mg.

13. 13. The negative electrode composite according to claim 11, wherein the negative electrode layer is a layer of a solid solution of Li and Mg.

14. The negative electrode composite according to claim 11, wherein the molar ratio of Li to Mg is Li:Mg=0.999:0.001-0.700:0.

300.

15. a negative electrode layer containing a negative electrode active material; a thin layer laminated on the negative electrode layer and containing Sn and / or an alloy of Sn and Li as a main component; wherein the negative electrode active material contains, as a main component, a solid solution in which an element M is dissolved in Li.

16. The alloy has a resistance of 10 Ωcm 2 16. The negative electrode composite of claim 15, exhibiting a resistance of:

17. 17. The negative electrode composite according to claim 15, wherein the thin layer has a thickness in the range of 100 to 500 nm.

18. The negative electrode composite according to any one of claims 1 to 17, which is used in a secondary battery.

19. The negative electrode composite according to claim 18 , wherein the secondary battery is an all-solid-state secondary battery.

20. The negative electrode composite according to any one of claims 1 to 17, an electrolyte layer in contact with the thin layer; a positive electrode composite containing a positive electrode active material; A secondary battery comprising:

21. 21. The secondary battery of claim 20, wherein the electrolyte layer comprises a solid electrolyte layer.

22. 22. The secondary battery according to claim 21, wherein the solid electrolyte layer comprises a sulfide-based solid electrolyte.

23. A negative electrode layer including a negative electrode active material containing, as a main component, a solid solution in which element M is solid-solved in Li; a thin layer laminated on the negative electrode layer and containing, as a main component, a material X having a higher oxidation-reduction potential than the negative electrode active material or having no electrode activity; a negative electrode composite comprising: an electrolyte layer in contact with the thin layer; a positive electrode composite containing a positive electrode active material; Equipped with A secondary battery in which the substance X is a metal or semimetal that can be alloyed with Li but is not solid-soluble in Li, and / or an alloy of the metal or semimetal with Li.

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