Negative electrode and secondary battery

Abstract

The present invention provides: a negative electrode which is capable of improving the cycle characteristics; and a secondary battery. A negative electrode according to the present invention is provided with: a negative electrode collector; a negative electrode active material layer; a first layer that is arranged between the negative electrode collector and the negative electrode active material layer; and a second layer that is arranged on the negative electrode active material layer. The negative electrode collector contains at least one element that is selected from among copper, nickel and iron; the negative electrode active material layer contains silicon; the first layer contains silicon, the metal element that constitutes the negative electrode collector, and at least one element that is selected from among titanium, nickel, zinc, silver, iron, boron, indium and germanium; and the second layer contains silicon and at least one element that is selected from among titanium, nickel, zinc, silver, iron, boron, indium and germanium.

Description

[Technical Field]

[0001] The present disclosure relates to a negative electrode and a secondary battery. [Background technology]

[0002] As shown in Patent Document 1, silicon is sometimes used as a main component of the negative electrode active material of a lithium ion secondary battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-183364 Summary of the Invention [Problem to be solved by the invention]

[0004] It is known that when silicon is used as the main component of the negative electrode active material in lithium-ion secondary batteries, silicon expands due to absorption of lithium ions during the initial charge / discharge cycle, which can lead to cracks in the negative electrode active material layer and separation between the negative electrode active material layer and the negative electrode current collector, resulting in a deterioration in cycle performance.

[0005] The present disclosure has been made in view of the above, and aims to provide a negative electrode and a secondary battery that can improve cycle characteristics. [Means for solving the problem]

[0006] A negative electrode according to one embodiment includes a negative electrode current collector, a negative electrode active material layer, a first layer disposed between the negative electrode current collector and the negative electrode active material layer, and a second layer disposed on the negative electrode active material layer, wherein the negative electrode current collector contains at least one of copper, nickel, and iron, the negative electrode active material layer contains silicon, the first layer contains silicon, metal elements constituting the negative electrode current collector, and at least one of titanium, nickel, zinc, silver, iron, boron, indium, and germanium, and the second layer contains silicon and at least one of titanium, nickel, zinc, silver, iron, boron, indium, and germanium.

[0007] A secondary battery according to one embodiment includes the negative electrode, a positive electrode, and an electrolyte. [Effects of the Invention]

[0008] According to the present invention, cycle characteristics can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a secondary battery according to a first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of a secondary battery according to the second embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of a secondary battery according to a third embodiment. [Figure 4] FIG. 4 is a schematic enlarged view of region A in FIG. [Figure 5] FIG. 5 is a schematic cutaway view showing an example of a secondary battery according to the fourth embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to these embodiments.

[0011] (First embodiment) FIG. 1 is a schematic cross-sectional view showing an example of a secondary battery according to the first embodiment. The secondary battery 1 according to the first embodiment is an all-solid-state battery in which the electrolyte is solid, and is a lithium-ion secondary battery. As shown in FIG. 1, the secondary battery 1 includes a protective layer 10, a positive electrode 20, a negative electrode 30, a solid electrolyte layer 40, and an insulating layer 50. In the example of FIG. 1, the secondary battery 1 has a structure in which the sheet-like positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40 are stacked.

[0012] In the drawings showing this embodiment, the Z direction refers to the stacking direction of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40, the X direction refers to a direction perpendicular to the Z direction and parallel to the cross section of FIG. 1, and the Y direction refers to a direction perpendicular to the X direction and the Z direction. In addition, in describing this embodiment, one of the X directions may be referred to as the +X direction and the other as the -X direction. Similarly, one of the Z directions may be referred to as the +Z direction and the other as the -Z direction.

[0013] The protective layer 10 is a layer provided to physically and chemically protect the secondary battery 1. In plan view in the Z direction, the protective layer 10 is provided so as to overlap the stack of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40, and in the example of FIG. 1 , the protective layer 10 is provided on both sides in the Z direction of the stack of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40. The material of the protective layer 10 is not particularly limited as long as it is insulating, and examples thereof include resin, glass, and ceramics.

[0014] The positive electrode 20 includes a positive electrode current collector layer 21 and a positive electrode active material layer 22. In the example of Fig. 1, the positive electrode 20 has a structure in which the positive electrode active material layer 22 is stacked in the -Z direction of the positive electrode current collector layer 21, but this is merely an example, and the positive electrode active material layer 22 may be stacked in the +Z direction of the positive electrode current collector layer 21.

[0015] The positive electrode current collector layer 21 is a layer having electrical conductivity. In the example of FIG. 1, the end face of the positive electrode current collector layer 21 in the +X direction is exposed and can be connected to the outside. That is, the end face of the positive electrode current collector layer 21 in the +X direction serves as the positive electrode of the secondary battery 1. The material of the positive electrode current collector layer 21 is not particularly limited as long as it has electrical conductivity, and examples thereof include metal materials such as silver, palladium, gold, platinum, aluminum, copper, and nickel, and carbon materials.

[0016] The positive electrode active material layer 22 is a layer containing a positive electrode active material. The positive electrode active material layer 22 is laminated on the positive electrode current collector layer 21. The positive electrode active material is not particularly limited, and may be at least one selected from the group consisting of a lithium-containing phosphate compound having a Nasicon structure, a lithium-containing phosphate compound having an olivine structure, a lithium-containing layered oxide, and a lithium-containing oxide having a spinel structure. An example of a lithium-containing phosphate compound having a Nasicon structure is Li3V2(PO4)3. An example of a lithium-containing phosphate compound having an olivine structure is Li3Fe2(PO4)3, LiMnPO4, etc. An example of a lithium-containing layered oxide is LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 Examples of lithium-containing oxides having a spinel structure include LiMn2O4, LiNi 0.5 Mn 1.5 Examples include O4.

[0017] The material contained in the positive electrode active material layer 22 is not limited to the positive electrode active material, and may also contain a solid electrolyte or a sintering aid, which will be described later. The sintering aid is not particularly limited, and examples thereof include lithium oxide, sodium oxide, potassium oxide, boron oxide, silicon oxide, bismuth oxide, and phosphorus oxide.

[0018] The negative electrode 30 includes a negative electrode current collector layer 31, a peeling prevention layer 32, a negative electrode active material layer 33, and a cap layer .

[0019] The negative electrode current collector layer 31 is a conductive layer. Here, the negative electrode current collector layer 31 is an example of a "negative electrode current collector." In the example of FIG. 1, the end face of the negative electrode current collector layer 31 in the -X direction is exposed and can be connected to the outside. That is, the end face of the negative electrode current collector layer 31 in the -X direction serves as the negative electrode of the secondary battery 1. In the example of FIG. 1, the thickness of the negative electrode current collector layer 31 is not particularly limited, but is preferably thicker than the negative electrode active material layer 33 described below, and is approximately 30 μm. The material of the negative electrode current collector layer 31 is a conductive metal and contains at least one metal selected from the group consisting of copper, nickel, and iron. However, the material of the negative electrode current collector layer 31 is not limited thereto and may further contain a metal material such as palladium, gold, platinum, or aluminum. Furthermore, the negative electrode current collector layer 31 is not limited to being composed of a single layer and may be composed of multiple layers, for example, stainless steel coated with nickel on the anti-peeling layer 32 side. In the following description, the material that constitutes the negative electrode current collector layer 31 may be referred to as the "negative electrode current collector material."

[0020] The peel-preventing layer 32 is a layer provided on the negative electrode current collector layer 31. The peel-preventing layer 32 is provided between the negative electrode current collector layer 31 and the negative electrode active material layer 33. Here, the peel-preventing layer 32 is an example of a "first layer." The thickness of the peel-preventing layer 32 is 5 nm or more and 55 nm or less. In the example of FIG. 1 , the peel-preventing layer 32 is provided in the +Z direction of the negative electrode current collector layer 31.

[0021] The peel-preventing layer 32 contains silicon, the negative electrode current collector material, and at least one of titanium (Ti), nickel (Ni), zinc (Zn), silver (Ag), iron (Fe), boron (B), indium (In), and germanium (Ge). This allows the peel-preventing layer 32 to suppress peeling between the negative electrode current collector layer 31 and the negative electrode active material layer 33 when the negative electrode active material layer 33 expands. This improves the cycle characteristics of the secondary battery 1. Herein, the elements constituting the peel-preventing layer 32, excluding silicon and the negative electrode current collector material, are preferably titanium. In this case, the resistance of the peel-preventing layer 32 can be reduced. In the following description, the elements constituting the peel-preventing layer 32, excluding silicon and the negative electrode current collector material, may be referred to as the "first metal."

[0022] The peel-preventing layer 32 contains silicon on the negative electrode active material layer 33 side. That is, silicon and the first metal are mixed on the negative electrode active material layer 33 side of the peel-preventing layer 32. The silicon concentration in the peel-preventing layer 32 can be measured by a composition analysis method in the depth direction, such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), or secondary ion mass spectrometry (SIMS). This allows the peel-preventing layer 32 to suppress the interfacial energy with the negative electrode active material layer 33, thereby further reducing the resistance between the negative electrode current collector layer 31 and the negative electrode active material layer 33. Furthermore, the peel-preventing layer 32 does not contain silicon on the negative electrode current collector layer 31 side. That is, the peel-preventing layer 32 can be considered a layer in which silicon is diffused only in the portion that contacts the negative electrode active material layer 33 in the thickness direction. Therefore, it can be said that the concentration of silicon contained in the peel-preventing layer 32 on the negative electrode active material layer 33 side is higher than the concentration of silicon contained in the peel-preventing layer 32 on the negative electrode current collector layer 31 side.

[0023] The peel-preventing layer 32 contains the negative electrode current collector material on the negative electrode current collector layer 31 side. That is, the negative electrode current collector material and the first metal are mixed on the negative electrode current collector layer 31 side of the peel-preventing layer 32. The concentration of the negative electrode current collector material in the peel-preventing layer 32 can be measured by a composition analysis method in the depth direction, such as XPS, AES, or SIMS. This allows the peel-preventing layer 32 to suppress the interfacial energy with the negative electrode current collector layer 31, thereby further reducing the resistance between the negative electrode current collector layer 31 and the negative electrode active material layer 33. Furthermore, the peel-preventing layer 32 does not contain the negative electrode current collector material on the negative electrode active material layer 33 side. That is, the peel-preventing layer 32 can be considered a layer in which the negative electrode current collector material is diffused only in the portion that contacts the negative electrode current collector layer 31 in the thickness direction. Therefore, it can be said that the concentration of the negative electrode current collector material contained in the anti-peeling layer 32 on the negative electrode current collector layer 31 side is higher than the concentration of the negative electrode current collector material contained in the anti-peeling layer 32 on the negative electrode active material layer 33 side.

[0024] The negative electrode active material layer 33 is a layer containing a negative electrode active material. In the example of Fig. 1, the negative electrode active material layer 33 is provided in the +Z direction of the peel-preventive layer 32. The thickness of the negative electrode active material layer 33 is 2 µm or more and 5 µm or less. This can improve the capacity of the secondary battery 1.

[0025] The negative electrode active material layer 33 contains silicon as the negative electrode active material. The crystallinity of the silicon is not particularly limited and may be, for example, amorphous. The negative electrode active material is preferably doped silicon. The dopant element of the silicon in the negative electrode active material can be at least one element selected from the group consisting of boron, phosphorus (P), aluminum, bismuth (Bi), lithium (Li), and oxygen (O). This can prevent the capacity of the secondary battery 1 from decreasing due to the dopant.

[0026] The cap layer 34 is a layer provided on the negative electrode active material layer 33. Here, the cap layer 34 is an example of a "second layer." In the example of FIG. 1, the cap layer 34 is provided in the +Z direction of the negative electrode active material layer 33. The thickness of the cap layer 34 is 5 nm or more and 55 nm or less.

[0027] The cap layer 34 contains silicon and at least one of titanium (Ti), nickel (Ni), zinc (Zn), silver (Ag), iron (Fe), boron (B), indium (In), and germanium (Ge). This provides the cap layer 34 with malleability. Therefore, even when the thickness of the anode active material layer 33 is 2 μm or greater, stress generated by the expansion of the anode active material layer 33 is applied to the malleable cap layer 34, which is less susceptible to cracking. This prevents cracking in the anode active material layer 33. This prevents damage to the anode active material layer 33, thereby improving the cycle characteristics of the secondary battery 1. Furthermore, when the anode active material layer 33 expands, the cap layer 34 deforms so as to be pressed against the solid electrolyte layer 40. This brings the cap layer 34 and the solid electrolyte layer 40 into close contact with each other, thereby reducing the interfacial resistance between the cap layer 34 and the solid electrolyte layer 40. Here, the element constituting the cap layer 34 other than silicon is preferably titanium. This reduces the resistance of the cap layer 34. Furthermore, the elements constituting the cap layer 34, excluding silicon, are preferably the same as the elements constituting the anti-peeling layer 32, excluding silicon and the negative electrode current collector material. This allows the stress of the negative electrode 30 to be uniformly relieved. In the following description, the elements constituting the cap layer 34, excluding silicon, may be referred to as the "second metal."

[0028] The cap layer 34 contains silicon throughout its thickness. This allows the cap layer 34 to further reduce the interfacial resistance with the solid electrolyte layer 40. The concentration of the second metal in the cap layer 34 preferably decreases toward the anode active material layer 33. That is, the cap layer 34 preferably has a silicon concentration gradient in the thickness direction, with the silicon concentration increasing toward the anode active material layer 33. The silicon concentration in the cap layer 34 can be measured by composition analysis in the depth direction using techniques such as XPS, AES, and SIMS. When the cap layer 34 has a concentration gradient, the stress in the cap layer 34 continuously changes in the Z direction, thereby further suppressing cracking due to stress in the anode active material layer 33. Furthermore, the concentration of the second metal continuously changes toward the anode active material layer 33, thereby suppressing the interfacial energy between the cap layer 34 and the anode active material layer 33 and reducing the interfacial resistance between the cap layer 34 and the anode active material layer 33. The silicon concentration in the cap layer 34 does not necessarily have to have a gradient in the thickness direction, but may be uniform.

[0029] 1, the negative electrode 30 has a structure in which the anti-peeling layer 32, the negative electrode active material layer 33, and the cap layer 34 are stacked in the +Z direction of the negative electrode current collector layer 31, but this is merely an example, and the layers may be stacked in the −Z direction of the negative electrode current collector layer 31.

[0030] The solid electrolyte layer 40 is a layer provided between the positive electrode 20 and the negative electrode 30. The solid electrolyte layer 40 is a sintered body containing a solid electrolyte. The material of the solid electrolyte is not particularly limited as long as it is a material that allows ions to move between the positive electrode 20 and the negative electrode 30. Examples of the material of the solid electrolyte include lithium-containing phosphate compounds having a Nasicon structure, oxides having a perovskite structure, and oxides having a garnet type or garnet-like structure. Examples of lithium-containing phosphate compounds having a Nasicon structure include Li x M y(PO4)3 (1≦x≦2, 1≦y≦2, M is at least one of Ti, Ge, Al, Ga, and Zr). An example of a lithium-containing phosphate compound having a Nasicon structure is Li 1.2 Al 0.2 Ti 1.8 (PO4), etc. An example of an oxide with a perovskite structure is La 0.55 Li 0.35 Examples of oxides with garnet or garnet-like structures include Li7La3Zr2O 12 The material of the solid electrolyte layer 40 is not limited to a solid electrolyte, and may include the sintering aid described above.

[0031] The side reinforcing portions 60 are provided to prevent short circuits in the secondary battery 1. In the example of Fig. 1, the side reinforcing portions 60 are provided on the end surfaces in the X direction and the Y direction of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40. The material of the side reinforcing portions 60 is not particularly limited as long as it is an insulating material, and examples thereof include resin, glass, and ceramics.

[0032] As described above, the negative electrode 30 according to this embodiment includes a negative electrode current collector (negative electrode current collector layer 31), a negative electrode active material layer 33, a first layer (anti-peeling layer 32) provided between the negative electrode current collector and the negative electrode active material layer 33, and a second layer (cap layer 34) provided on the negative electrode active material layer 33. The negative electrode current collector includes a negative electrode current collector material that is at least one metal selected from the group consisting of copper, nickel, and iron. The negative electrode active material layer 33 includes silicon. The first layer includes silicon, metal elements constituting the negative electrode current collector, and at least one metal selected from the group consisting of titanium, nickel, zinc, silver, iron, boron, indium, and germanium. The second layer includes silicon, and at least one metal selected from the group consisting of titanium, nickel, zinc, silver, iron, boron, indium, and germanium.

[0033] As a result, even if the negative electrode active material layer 33 expands, the second layer can prevent cracks from occurring in the negative electrode active material layer 33, and the first layer can prevent peeling between the negative electrode current collector and the negative electrode active material layer 33, thereby improving the cycle retention rate.

[0034] In a preferred embodiment, the elements constituting the first layer, excluding silicon and the metal constituting the negative electrode current collector, are the same as the elements constituting the second layer, excluding silicon, which allows the stress of the negative electrode 30 to be uniformly relieved.

[0035] In a more preferred embodiment, the elements constituting the first layer, excluding silicon and the metal constituting the negative electrode current collector, are titanium, and the elements constituting the second layer, excluding silicon, are titanium, thereby reducing the resistance of the first layer and the second layer.

[0036] In a preferred embodiment, the silicon concentration on the anode active material layer side of the first layer is higher than the silicon concentration on the anode current collector side of the first layer, the concentration of the anode current collector material on the anode current collector side of the first layer is higher than the concentration of the anode current collector material on the anode active material layer 33 side of the first layer, and the second layer contains silicon throughout the entire thickness direction. This can further reduce the interfacial energy between the cap layer 34 and the anode active material layer 33, and further reduce the interfacial resistance between the second layer and the anode active material layer 33. Furthermore, because the silicon concentration of the first layer changes continuously in the direction of the anode active material layer 33, the interfacial energy with the anode active material layer 33 can further be reduced, and the resistance between the anode current collector and the anode active material layer 33 can further be reduced. Furthermore, since the concentration of the negative electrode current collector material in the first layer changes continuously in the direction in which the negative electrode current collector is provided, the interfacial energy with the negative electrode current collector can be further suppressed, and the resistance between the negative electrode current collector and the negative electrode active material layer 33 can be further reduced.

[0037] Moreover, the secondary battery 1 according to this embodiment includes a positive electrode 20, a negative electrode 30, and an electrolyte (solid electrolyte layer 40). This configuration can improve the cycle retention rate.

[0038] (Method of manufacturing negative electrode) The negative electrode 30 according to this embodiment is produced, for example, by the following method.

[0039] First, in the lamination process, a first metal layer, a silicon-containing layer, and a second metal layer are laminated in this order on the negative electrode current collector layer 31. The lamination process is performed without contact with air, and the layers are laminated by a method such as sputtering, chemical vapor deposition, or ion plating. The first metal layer is a layer made of a first metal and has a thickness of 0.1 μm or more and 1 μm or less. Here, the second metal layer is a layer made of a second metal and has a thickness of 0.1 μm or more and 1 μm or less. The silicon-containing layer is a layer made of a material containing silicon, such as a layer of a mixture of silicon and a dopant. In this case, silicon and a dopant are mixed by being laminated simultaneously on the first metal layer.

[0040] Next, the laminate including the negative electrode current collector layer 31 is annealed. By the annealing, the silicon-containing layer becomes doped silicon, the first metal of the first metal layer becomes the anti-peeling layer 32, and the second metal of the second metal layer diffuses into the silicon-containing layer to form the cap layer 34. The annealing conditions are set so that silicon is contained throughout the entire thickness of the cap layer 34. Here, the portion of the silicon-containing layer into which the first metal or the second metal has not diffused becomes the negative electrode active material layer 33.

[0041] (Second embodiment) FIG. 2 is a schematic cross-sectional view showing an example of a secondary battery according to the second embodiment. The secondary battery according to this embodiment will be described below. Note that similar components are denoted by the same reference numerals and description thereof will be omitted. The secondary battery 1A according to the second embodiment differs from the secondary batteries 1 according to the first and second embodiments in that the negative electrode 30A includes a plurality of negative electrode active material layers 33a-33d and a plurality of cap layers 34a-34d. Here, the cap layers 34a-34d are an example of a "second layer." The thickness of each of the plurality of negative electrode active material layers 33a-33d and the plurality of cap layers 34a-34d is smaller than the thickness of the peel-preventive layer 32.

[0042] 2, in the secondary battery 1A according to the second embodiment, the negative electrode active material layers 33a to 33d and the cap layers 34a to 34d are stacked in the +Z direction of the peel-preventing layer 32 in the following order: negative electrode active material layer 33d, cap layer 34d, negative electrode active material layer 33c, cap layer 34c, negative electrode active material layer 33b, cap layer 34b, negative electrode active material layer 33a, and cap layer 34a. That is, in the secondary battery 1A, the cap layers 34a to 34d are stacked alternately with the negative electrode active material layers 33a to 33d in the Z direction.

[0043] With this structure, the cap layers 34b-34d can suppress peeling between the negative electrode active material layers 33a-33d, thereby improving the cycle characteristics of the secondary battery 1A. Furthermore, the second metal contained in the cap layers 34b-34d acts as a surfactant for the silicon-containing layer in the production of the negative electrode 30A, thickening the silicon-containing layer and improving the capacity of the secondary battery 1. More specifically, in the production of the negative electrode 30A, by laminating the second metal layer on the silicon-containing layer, the surface energy of the first silicon-containing layer is reduced, and the second silicon-containing layer laminated on the second metal layer is facilitated to be thickened.

[0044] (Third embodiment) FIG. 3 is a schematic cross-sectional view showing an example of a secondary battery according to a third embodiment. The secondary battery 100 according to the third embodiment is a cylindrical battery and includes a liquid electrolyte. As shown in FIG. 3, the secondary battery 200 includes a casing 110, a positive electrode 120, a negative electrode 130, and a separator 150. The casing 110 is a case that houses an electrode assembly and an electrolyte (not shown). The casing 110 includes a battery can 111, a lid 112, a thermosensitive resistor 113, a safety valve mechanism 114, a gasket 115, a positive electrode lead 116, a negative electrode lead 117, a center pin 119, and an insulating plate 118.

[0045] The battery can 111 is a cylindrical member that includes an end face that serves as the negative electrode of the secondary battery 100. That is, the battery can 111 is a cylinder with one end face closed and the other end face open. The battery can 111 is a conductor, and for example, the surface of an iron (Fe) base material is plated with nickel (Ni).

[0046] The lid body 112 is a disk-shaped member including a protrusion that serves as the positive electrode of the secondary battery 100. The lid body 112 is provided on the end face on the open side of the battery can 111. The lid body 112 is made of metal, for example, the same material as the battery can 111.

[0047] In the description of this embodiment, the direction in which the cylindrical portion of the battery can 111 extends may be described as the length direction of the secondary battery 100. The positive electrode of the secondary battery 100 refers to the protrusion of the lid 112, and the negative electrode of the secondary battery 100 refers to the closed end surface of the battery can 111.

[0048] The thermosensitive resistor 113 is an element whose resistance increases with an increase in temperature. The thermosensitive resistor 113 is provided on the negative electrode side of the lid 112. When the secondary battery 100 becomes hot due to a short circuit or the like, the resistance value of the thermosensitive resistor 113 increases and limits the current.

[0049] The safety valve mechanism 114 is a mechanism that changes shape in response to the gas pressure inside the casing 110. The safety valve mechanism 114 is provided on the negative electrode side with respect to the thermosensitive resistor element 113. The safety valve mechanism 114 is electrically connected to the lid 112 via the thermosensitive resistor element 113. The safety valve mechanism 114 has a protrusion on the negative electrode side, and when the gas pressure inside the casing 110 is normal, the safety valve mechanism 114 is in contact with and electrically connected to the positive electrode lead 116 via the protrusion. On the other hand, when the gas pressure inside the casing 110 increases, the protrusion of the safety valve mechanism 114 reverses to the positive electrode side and moves away from the positive electrode lead 116, thereby electrically disconnecting the positive electrode lead 116 from the lid 112.

[0050] The gasket 115 is an annular member that fixes the lid 112, the thermosensitive resistor 113, and the safety valve mechanism 114 to the battery can 111. The gasket 115 is provided on the open end surface of the battery can 111. The gasket 115 tightly contacts the battery can 111 and the lid 112, making the inside of the casing 110 airtight. The gasket 115 is an insulator.

[0051] The positive electrode lead 116 is a terminal connected to a positive electrode 120 of the electrode body, which will be described later. The positive electrode lead 116 is electrically connected to the lid body 112 via a safety valve mechanism 114 and a thermosensitive resistor element 113. The positive electrode lead 116 is a conductor, for example, aluminum (Al).

[0052] The negative electrode lead 117 is a terminal connected to the negative electrode 130 of the electrode assembly, which will be described later. The negative electrode lead 117 is electrically connected to the battery can 111. The negative electrode lead 117 is a conductor, such as nickel (Ni).

[0053] The insulating plate 118 is a plate-shaped member that is an insulator. Two insulating plates 118 are provided so as to cover the cross section of the electrode body (described later) on the positive electrode side of the secondary battery 100 and the cross section of the electrode body (described later) on the negative electrode side of the secondary battery 100, respectively.

[0054] The center pin 119 is provided on the central axis of the electrode body. The center pin 119 is a linear member having a length in the longitudinal direction of the secondary battery 100. The material of the center pin 119 is not particularly limited, and may be, for example, a metal.

[0055] Fig. 4 is an enlarged view of region A in Fig. 3. As shown in Fig. 3 and Fig. 4, the positive electrode 120 and the negative electrode 130 according to the third embodiment are stacked with a separator 150 interposed therebetween, and are provided inside a battery can 111. In the example of Fig. 3, the positive electrode 120, the negative electrode 130, and the separator 150 are stacked in the radial direction of the secondary battery 100 with a center pin 119 as the center.

[0056] The positive electrode 120 includes a positive electrode current collector layer 121 and a positive electrode active material layer 122. In the positive electrode 120, the positive electrode current collector layer 121 is laminated on two positive electrode active material layers 122. The material and thickness of the positive electrode current collector layer 121 are the same as those of the positive electrode current collector layer 21 in the first embodiment. The material and thickness of the positive electrode active material layer 122 are the same as those of the positive electrode active material layer 22 in the first embodiment.

[0057] The negative electrode 130 includes a negative electrode current collector layer 131 and a negative electrode material layer 132. Here, the negative electrode current collector layer 131 is an example of a "negative electrode current collector." In the negative electrode 130, the negative electrode current collector layer 131 is laminated on two negative electrode material layers 132. The negative electrode current collector layer 131 is made of the same material as the negative electrode current collector layer 31 in the first embodiment. The negative electrode material layer 132 is a layer including a negative electrode active material layer. The negative electrode material layer 132 includes a peeling prevention layer, a negative electrode active material layer, and a cap layer, all of which are made of the same materials as in the first embodiment. In other words, the peeling prevention layer is an example of a "first layer," and the cap layer is an example of a "second layer." Here, the cap layer is thinner than the peeling prevention layer. The negative electrode material layer 132 is a laminate formed by laminating, in this order from the negative electrode current collector layer 131 side, a peel-preventing layer, a negative electrode active material layer, and a cap layer. As a result, even if the negative electrode active material layer expands, the provision of the peel-preventing layer can prevent the negative electrode material layer 132 from peeling off from the negative electrode current collector layer 131. Furthermore, even if cracks occur in the negative electrode active material layer due to expansion, the provision of the cap layer can prevent the electrolyte solution from penetrating the cracks and forming a coating on the newly formed surface within the cracks, thereby preventing deterioration of the negative electrode active material. Therefore, the cycle characteristics of the secondary battery 100 can be improved.

[0058] The separator 150 is a layer that insulates the positive electrode 120 and the negative electrode 130. The separator 150 is provided to prevent direct contact between the positive electrode 120 and the negative electrode 130 and is laminated between the positive electrode 120 and the negative electrode 130 in the electrode assembly. The material of the separator 150 is preferably electrically stable, chemically stable against the positive electrode active material, the negative electrode active material, and the electrolyte, and insulating. The separator 150 can be, for example, a layer made of polymer nonwoven fabric, porous film, glass, or ceramic fibers. The material of the separator 150 more preferably includes a porous polyolefin film. The separator 150 may also be made of multiple layers, or a composite of a porous polyolefin film and a heat-resistant film containing polyimide, glass, or ceramic fibers may be used.

[0059] The electrolyte is filled in the space surrounded by the insulating plate 118 and the battery can 111. The electrolyte includes an electrolyte salt and a solvent that dissolves the electrolyte salt. The electrolyte salt includes a lithium salt such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium bis(trifluoromethanesulfonyl)imide (LiN(SOCF)), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SOCF)), or lithium hexafluoroarsenate (LiAsF). Examples of the solvent include lactone-based solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone; carbonate-based solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; ether-based solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitrile-based solvents such as acetonitrile; sulfolane-based solvents; phosphoric acids; phosphate ester solvents; and non-aqueous solvents such as pyrrolidones.

[0060] (Fourth embodiment) Fig. 5 is a cutaway view showing an example of a secondary battery according to a fourth embodiment. Fig. 6 is a schematic cross-sectional view taken along line VI-VI in Fig. 5. A secondary battery 200 according to the fourth embodiment includes a gel electrolyte. As shown in Figs. 5 and 6, the secondary battery 200 according to the fourth embodiment includes a battery element, an exterior member 211, an adhesive 212, a protective material 213, a positive electrode 220, a negative electrode 230, a gel electrolyte layer 240, a separator 250, a positive electrode lead 260, and a negative electrode lead 270.

[0061] The exterior member 211 is a case for the secondary battery 200. The exterior member 211 includes an insulating layer, a metal layer, and an outermost layer. The exterior member 211 is structured by laminating the insulating layer, metal layer, and outermost layer in this order from the inside out, and then bonding them together by lamination or other processes. The insulating layer of the exterior member 211 is made of a resin such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or a polyolefin resin containing ethylene or propylene as a monomer. This allows the exterior member 211 to reduce the moisture permeability of the secondary battery 200 and improve its airtightness. The metal layer of the exterior member 211 is a plate or foil film made of a metal such as aluminum, stainless steel, nickel, or iron. The outermost layer may be made of any material, but is preferably made of a resin similar to that of the insulating layer or a material with high resistance to tearing, punctures, etc., such as nylon.

[0062] The adhesive 212 is a member for making the exterior member 211 airtight. The adhesive 212 is provided between the exterior member 211 and the positive electrode lead 260 and the negative electrode lead 270. The material of the adhesive 212 preferably has adhesion to the positive electrode lead 260 and the negative electrode lead 270. For example, when the positive electrode lead 260 and the negative electrode lead 270 are metals, the adhesive 212 is made of a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene. This makes it possible to seal the gap between the exterior member 211 and the positive electrode lead 260 or the negative electrode lead 270, thereby making the interior of the exterior member 211 airtight.

[0063] The positive electrode 220 includes a positive electrode current collector layer 221 and a positive electrode active material layer 222. The material and thickness of the positive electrode current collector layer 221 are the same as those of the positive electrode current collector layer 21 in the first embodiment. The material and thickness of the positive electrode active material layer 222 are the same as those of the positive electrode active material layer 22 in the first embodiment.

[0064] The negative electrode 230 includes a negative electrode current collector layer 231 and a negative electrode material layer 232. Here, the negative electrode current collector layer 131 is an example of a "negative electrode current collector." The negative electrode current collector layer 131 includes a peel-preventing layer, a negative electrode active material layer, and a cap layer, which are made of the same materials as those in the first embodiment. That is, the peel-preventing layer is an example of a "first layer," and the cap layer is an example of a "second layer." Here, the cap layer is thinner than the peel-preventing layer. Similarly to the negative electrode material layer 132 in the third embodiment, the negative electrode material layer 232 is a laminate in which the peel-preventing layer, the negative electrode active material layer, and the cap layer are stacked in this order from the negative electrode current collector layer 231 side. As a result, even if the negative electrode active material layer expands, the presence of the peel-preventing layer prevents the negative electrode material layer 132 from peeling off from the negative electrode current collector layer 131. Furthermore, even if cracks occur in the negative electrode active material layer due to expansion, the provision of the cap layer can prevent the electrolyte gel from entering the cracks and thereby preventing deterioration of the negative electrode active material, thereby improving the cycle characteristics of the secondary battery 200.

[0065] 6, the positive electrode 220, the negative electrode 230, the gel electrolyte layer 240, and the separator 250 are wound around the positive electrode lead 260 and the negative electrode lead 270. From the outside, i.e., from the protective material 213 side, the negative electrode current collector layer 231, the negative electrode material layer 232, the gel electrolyte layer 240, the separator 250, the gel electrolyte layer 240, the positive electrode active material layer 222, the positive electrode current collector layer 221, the positive electrode active material layer 222, the gel electrolyte layer 240, the separator 250, the gel electrolyte layer 240, and the negative electrode material layer 232 are laminated in this order.

[0066] The gel electrolyte layer 240 is a layer that serves as the electrolyte of the secondary battery 200. The gel electrolyte layer 240 is a gel-like layer made of a polymer compound that retains an electrolyte solution. The polymer compound used as the gel of the gel electrolyte layer 240 can be any polymer compound that absorbs a solvent and gels. Examples include fluorine-based polymer compounds such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, ether-based polymer compounds such as polyethylene oxide or a crosslinked product containing polyethylene oxide, and polymer compounds containing polyacrylonitrile, polypropylene oxide, or polymethyl methacrylate as a monomer. The polymer compound used as the gel of the gel electrolyte layer 240 is preferably a fluorine-based polymer compound, and more preferably a copolymer containing vinylidene fluoride and hexafluoropropylene as monomers. Using this material can improve stability against redox reactions. Here, the copolymer of the polymer compound used as the gel of the gel electrolyte layer 240 may further contain, as a monomer, a monoester of an unsaturated dibasic acid such as monomethyl maleate ester, an ethylene halide such as trifluorochloroethylene, a cyclic carbonate of an unsaturated compound such as vinylene carbonate, or an epoxy group-containing acrylic vinyl monomer, etc. In this case, the cycle characteristics can be improved.

[0067] The positive electrode lead 260 is a terminal drawn from the positive electrode current collector layer 221 to the outside of the exterior member 211. That is, the positive electrode lead 260 is a terminal that serves as the positive electrode of the secondary battery 200. In FIG. 6, the positive electrode lead 260 is provided near the center of the portion surrounded by the protective material 213. The material of the positive electrode lead 260 is the same as that of the positive electrode lead 116 in the third embodiment.

[0068] The negative electrode lead 270 is a terminal drawn from the negative electrode current collector layer 231 to the outside of the exterior member 211. That is, the negative electrode lead 270 is a terminal that serves as the negative electrode of the secondary battery 200. In FIG. 6, the negative electrode lead 270 is provided near the center of the portion surrounded by the protective material 213. The material of the negative electrode lead 270 is the same as that of the positive electrode lead 116 in the third embodiment.

[0069] The protective material 213 is a member that protects the secondary battery 200. The protective material 213 is provided so as to be wrapped around the negative electrode 230. The protective material 213 is, for example, an insulating tape.

[0070] The above-described embodiments are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present disclosure. [Explanation of symbols]

[0071] 1, 1A secondary battery 10 protective layer 20 positive electrode 21 Positive electrode current collector layer 22 Cathode active material layer 30, 30A negative pole 31 Negative electrode current collector layer 32 Anti-peeling layer 33, 33a~33d Negative electrode active material layer 34, 34a-34d Cap layer 40 Solid electrolyte layer 50 insulating layer 60 Side reinforcement 100 Secondary battery 110 Casing 111 Battery can 112 Lid 113 Thermal Resistance Element 114 Safety valve mechanism 115 Gasket 116 Positive lead 117 Negative lead 118 Insulating plate 119 Center Pin 120 positive electrode 121 Positive electrode current collector layer 122 Cathode active material layer 130 negative electrode 131 Negative electrode current collector layer 132 Negative electrode material layer 150 Separator 200 Secondary battery 211 Exterior materials 212 Adhesion material 213 Protective Materials 220 Positive electrode 221 Positive electrode current collector layer 222 Cathode active material layer 230 negative electrode 231 Negative electrode current collector layer 232 Negative electrode material layer 240 Gel electrolyte layer 250 Separator 260 Positive lead 270 Negative lead

Claims

1. a negative electrode current collector; a negative electrode active material layer; a first layer provided between the negative electrode current collector and the negative electrode active material layer; a second layer provided on the negative electrode active material layer; Equipped with the negative electrode current collector, the first layer, the negative electrode active material layer, and the second layer are laminated in this order; the negative electrode current collector contains at least one of copper, nickel, and iron, the negative electrode active material layer contains silicon, the first layer contains silicon, a metal element constituting the negative electrode current collector, and at least one of titanium, nickel, zinc, silver, iron, boron, indium, and germanium; The second layer comprises silicon and at least one of titanium, nickel, zinc, silver, iron, boron, indium, and germanium.

2. 2. The negative electrode according to claim 1, wherein elements constituting the first layer, excluding silicon and a metal constituting the negative electrode current collector, are the same as elements constituting the second layer, excluding silicon.

3. the element constituting the first layer, excluding silicon and the metal constituting the negative electrode current collector, is titanium; The negative electrode according to claim 2 , wherein the element constituting the second layer, excluding silicon, is titanium.

4. a concentration of silicon contained in the first layer on the negative electrode active material layer side is higher than a concentration of silicon contained in the first layer on the negative electrode current collector side; a concentration of the metal constituting the negative electrode current collector contained in the first layer on the negative electrode current collector side is higher than a concentration of the metal constituting the negative electrode current collector contained in the first layer on the negative electrode active material layer side, The negative electrode according to claim 1 , wherein the second layer contains silicon throughout its thickness.

5. A secondary battery comprising the negative electrode according to claim 1 , a positive electrode, and an electrolyte.

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