Negative electrode and secondary battery

Abstract

Provided are a negative electrode and a secondary battery with which cycle characteristics can be improved. The negative electrode is provided with: 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; and a second layer provided on the negative electrode active material layer. The negative electrode current collector contains at least one of copper, nickel and iron, the negative electrode active material layer contains silicon, and 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 includes silicon and at least one of 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 Art

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

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-183364 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] It is known that when silicon is used as the main component of the negative electrode active material of lithium ion secondary batteries, silicon expands due to absorption of lithium ions during the initial charge and discharge. Therefore, there is a concern that the negative electrode active material layer may crack or the negative electrode active material layer may be separated from the negative electrode current collector, resulting in a decrease in cycle characteristics.

[0008] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a negative electrode and a secondary battery capable of improving cycle characteristics.

[0009] Technical solutions for solving technical problems

[0010] On the one hand, the negative electrode involved comprises: a negative electrode collector; a negative electrode active material layer; a first layer, arranged between the negative electrode collector and the negative electrode active material layer; and a second layer, arranged in the negative electrode active material layer, the negative electrode 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 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.

[0011] A secondary battery according to one aspect includes the negative electrode, a positive electrode, and an electrolyte.

[0012] Effects of the Invention

[0013] According to the present invention, the cycle characteristics can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic cross-sectional view showing an example of the secondary battery according to the first embodiment.

[0015] Figure 2This is a schematic cross-sectional view showing an example of a secondary battery according to the second embodiment.

[0016] Figure 3 This is a schematic cross-sectional view showing an example of a secondary battery according to a third embodiment.

[0017] Figure 4 yes Figure 3 Schematic enlarged view of area A.

[0018] Figure 5 This is a schematic cross-sectional view showing an example of a secondary battery according to a fourth embodiment.

[0019] Figure 6 yes Figure 5 Schematic cross-sectional view taken along line VI-VI. DETAILED DESCRIPTION

[0020] The following describes an embodiment of the present disclosure. It should be noted that the embodiment does not limit the present disclosure.

[0021] (First embodiment)

[0022] Figure 1 1 is a schematic cross-sectional view showing an example of a secondary battery according to the first embodiment. The secondary battery 1 in the first embodiment is an all-solid-state battery in which the electrolyte is solid, and is a lithium-ion secondary battery. Figure 1 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. Figure 1 In the example of FIG. 1 , the secondary battery 1 has a structure in which a sheet-like positive electrode 20 , a negative electrode 30 , and a solid electrolyte layer 40 are stacked.

[0023] In the drawings showing the present embodiment, the Z direction refers to the stacking direction of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40, and the X direction refers to the direction perpendicular to the Z direction and parallel to the solid electrolyte layer 40. Figure 1 The Y direction refers to a direction parallel to the cross section of the X direction and the Z direction, and the Y direction refers to a direction orthogonal to the X direction and the Z direction. In addition, in the description of 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.

[0024] The protective layer 10 is a layer provided to physically and chemically protect the secondary battery 1. The protective layer 10 is provided so as to overlap with the stack of the positive electrode 20, the negative electrode 30, and the solid electrolyte layer 40 when viewed from the Z direction. Figure 1In the example, 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 is, for example, resin, glass, ceramic, etc.

[0025] The positive electrode 20 includes a positive electrode current collector layer 21 and a positive electrode active material layer 22. Figure 1 In the example, the positive electrode 20 is a structure obtained by stacking the positive electrode active material layer 22 in the -Z direction of the positive electrode collector layer 21, but this is only an example after all, and the positive electrode active material layer 22 can also be stacked in the +Z direction of the positive electrode collector layer 21.

[0026] The positive electrode current collector layer 21 is a conductive layer. Figure 1 In the example, the end face of the positive electrode collector layer 21 in the +X direction is exposed, and the positive electrode collector layer 21 can be connected to the outside. That is, the end face of the positive electrode collector layer 21 in the +X direction becomes the + pole of the secondary battery 1. The material of the positive electrode collector layer 21 is not particularly limited as long as it is a conductive material, and metal materials such as silver, palladium, gold, platinum, aluminum, copper, nickel, and carbon materials can be listed.

[0027] The positive electrode active material layer 22 is a layer containing a positive electrode active material. The positive electrode active material layer 22 is stacked on the positive electrode collector layer 21. The positive electrode active material is not particularly limited, and for example, 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 can be listed. As an example of a lithium-containing phosphate compound having a NASICON structure, Li3V2(PO4)3 and the like can be listed. As an example of a lithium-containing phosphate compound having an olivine structure, Li3Fe2(PO4)3, LiMnPO4 and the like can be listed. As an example of a lithium-containing layered oxide, LiCoO2, LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, etc. As an example of lithium-containing oxides having a spinel structure, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.

[0028] It should be noted that 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 and a sintering aid described below. 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.

[0029] The negative electrode 30 includes a negative electrode current collector layer 31 , an anti-peeling layer 32 , a negative electrode active material layer 33 , and a cap layer 34 .

[0030] 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". Figure 1 In the example, the end face of the negative electrode current collector layer 31 in the -X direction is exposed, and the negative electrode current collector layer 31 can be connected to the outside. That is, the end face of the negative electrode current collector layer 31 in the -X direction becomes the - pole of the secondary battery 1. Figure 1 In the example, the thickness of the negative electrode 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 collector layer 31 is a conductive metal, including at least one of copper, nickel, and iron. It should be noted that the material of the negative electrode collector layer 31 is not limited to this, for example, it may further include metal materials such as palladium, gold, platinum, and aluminum. In addition, the negative electrode collector layer 31 is not limited to being composed of one layer, for example, it may also be a collector layer having multiple layers such as stainless steel coated with nickel on the side of the anti-peeling layer 32. In the following description, the material constituting the negative electrode collector layer 31 is sometimes described as a "negative electrode collector material".

[0031] The anti-peeling layer 32 is a layer provided on the negative electrode current collector layer 31. The anti-peeling layer 32 is provided between the negative electrode current collector layer 31 and the negative electrode active material layer 33. Here, the anti-peeling layer 32 is an example of a "first layer". The thickness of the anti-peeling layer 32 is 5 nm or more and 55 nm or less. Figure 1 In the example of FIG. 5 , the anti-peeling layer 32 is provided in the +Z direction of the negative electrode current collector layer 31 .

[0032] The anti-peeling layer 32 contains silicon, a negative electrode collector material, and at least one of titanium (Ti), nickel (Ni), zinc (Zn), silver (Ag), iron (Fe), boron (B), indium (In), and germanium (Ge). Thus, the anti-peeling layer 32 can inhibit the negative electrode collector layer 31 from peeling off from the negative electrode active material layer 33 when the negative electrode active material layer 33 expands. Thus, the cycle characteristics of the secondary battery 1 can be improved. Here, the element constituting the anti-peeling layer 32 other than silicon and the negative electrode collector material is preferably titanium. In this case, the resistance of the anti-peeling layer 32 can be reduced. In the following description, the element constituting the anti-peeling layer 32 other than silicon and the negative electrode collector material is sometimes described as a "first metal".

[0033] The anti-peeling layer 32 contains silicon on the negative electrode active material layer 33 side. That is, on the negative electrode active material layer 33 side of the anti-peeling layer 32, silicon and the first metal are mixed. Here, the concentration of silicon in the anti-peeling layer 32 can be measured by a composition analysis method for the depth direction such as XPS (X-ray Photoelectron Spectroscopy), AES (Auger Electron Spectroscopy), SIMS (Secondary Ion Mass Spectrometry), etc. As a result, the anti-peeling layer 32 can suppress the interface energy with the negative electrode active material layer 33 and can further reduce the resistance between the negative electrode collector layer 31 and the negative electrode active material layer 33. In addition, the anti-peeling layer 32 does not contain silicon on the negative electrode collector layer 31 side. That is, the anti-peeling layer 32 can be said to be a layer in which silicon is diffused only in the portion that is in contact with the negative electrode active material layer 33 in the thickness direction. Therefore, it can be said that the concentration of silicon contained in the separation preventing layer 32 on the negative electrode active material layer 33 side is higher than the concentration of silicon contained in the separation preventing layer 32 on the negative electrode current collector layer 31 side.

[0034] The anti-peeling layer 32 contains a negative electrode collector material on the negative electrode collector layer 31 side. That is, on the negative electrode collector layer 31 side of the anti-peeling layer 32, the negative electrode collector material and the first metal are mixed together. Here, the concentration of the negative electrode collector material of the anti-peeling layer 32 can be measured by a composition analysis method for the depth direction such as XPS, AES, SIMS, etc. As a result, the anti-peeling layer 32 can suppress the interfacial energy with the negative electrode collector layer 31, and can further reduce the resistance between the negative electrode collector layer 31 and the negative electrode active material layer 33. In addition, the anti-peeling layer 32 does not contain a negative electrode collector material on the negative electrode active material layer 33 side. That is, the anti-peeling layer 32 can be said to be a layer in which the negative electrode collector material is diffused only in the portion that is in contact with the negative electrode collector layer 31 in the thickness direction. Therefore, it can be said that the concentration of the negative electrode collector material contained in the separation preventing layer 32 on the negative electrode collector layer 31 side is higher than the concentration of the negative electrode collector material contained in the separation preventing layer 32 on the negative electrode active material layer 33 side.

[0035] The negative electrode active material layer 33 is a layer containing a negative electrode active material. Figure 1 In the example of , the negative electrode active material layer 33 is provided in the +Z direction of the peeling-preventing layer 32. The thickness of the negative electrode active material layer 33 is 2 μm or more and 5 μm or less. Thus, the capacity of the secondary battery 1 can be increased.

[0036] The negative electrode active material layer 33 contains silicon as a negative electrode active material. The crystallinity of silicon is not particularly limited, and for example, it may be amorphous. The negative electrode active material is preferably doped silicon. The doping element of silicon in the negative electrode active material can use at least one element of boron, phosphorus (P), aluminum, bismuth (Bi), lithium (Li) and oxygen (O). Thus, the low capacity of the secondary battery 1 caused by doping can be suppressed.

[0037] 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". Figure 1 In the example of , 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.

[0038] The cap layer 34 includes silicon and at least one of titanium (Ti), nickel (Ni), zinc (Zn), silver (Ag), iron (Fe), boron (B), indium (In) and germanium (Ge). Thus, the cap layer 34 has ductility. For this reason, even when the thickness of the negative electrode active material layer 33 is set to 2 μm or more, since the stress generated by the expansion of the negative electrode active material layer 33 is applied to the cap layer 34 which is not easy to crack due to its ductility, the cracking of the negative electrode active material layer 33 can be suppressed. Therefore, the damage of the negative electrode active material layer 33 can be suppressed, so the cycle characteristics of the secondary battery 1 can be improved. In addition, when the negative electrode active material layer 33 expands, the cap layer 34 is deformed in a manner of being pressed against the solid electrolyte layer 40, so that the cap layer 34 and the solid electrolyte layer 40 are closely attached, and the interface resistance between the cap layer 34 and the solid electrolyte layer 40 can be reduced. Here, the element constituting the cap layer 34 other than silicon is preferably titanium. Thus, the resistance of the cap layer 34 can be reduced. In addition, the element constituting the cap layer 34 other than silicon is preferably the same as the element constituting the anti-peeling layer 32 other than silicon and the negative electrode current collector material. Thereby, the stress of the negative electrode 30 can be uniformly relaxed. In the following description, the element constituting the cap layer 34 other than silicon may be described as a "second metal".

[0039] The cap layer 34 contains silicon throughout the thickness direction. Thus, the cap layer 34 can further reduce the interface resistance with the solid electrolyte layer 40. In addition, the concentration of the second metal in the cap layer 34 preferably decreases as it approaches the negative electrode active material layer 33. That is, the cap layer 34 preferably has a concentration gradient of silicon in the thickness direction, and the concentration of silicon increases as it approaches the negative electrode active material layer 33. Here, the concentration of silicon in the cap layer 34 can be measured by composition analysis in the depth direction such as XPS, AES, SIMS, etc. In the case where the cap layer 34 has a concentration gradient, the cap layer 34 can further suppress cracking due to the stress of the negative electrode active material layer 33 because the stress of the layer changes continuously in the Z direction. In addition, since the concentration of the second metal changes continuously in the direction of the negative electrode active material layer 33, the interface energy between the cap layer 34 and the negative electrode active material layer 33 can be suppressed, and the interface resistance between the cap layer 34 and the negative electrode active material layer 33 can be reduced. It should be noted that the concentration of silicon in the cap layer 34 is not limited to having a gradient in the thickness direction, but can also be uniform.

[0040] It should be noted that the configuration of the negative electrode 30 is not limited to the configuration described above. Figure 1 In the example, the negative electrode 30 is a structure obtained by stacking an anti-peeling layer 32, a negative electrode active material layer 33 and a covering layer 34 in the +Z direction of the negative electrode collector layer 31, but it is only an example after all, and the negative electrode collector layer 31 can also be stacked in the -Z direction.

[0041] 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). As an example of a lithium-containing phosphate compound having a NASICON structure, for example, Li 1.2 Al 0.2 Ti 1.8 (PO4), etc. As an example of an oxide having a perovskite structure, La 0.55 Li 0.35 TiO3, etc. As an example of an oxide having a garnet-type or garnet-like structure, Li7La3Zr2O 12It should be noted that the material of the solid electrolyte layer 40 is not limited to the solid electrolyte, and may include the above-mentioned sintering aid.

[0042] The side reinforcement 60 is provided to prevent the secondary battery 1 from short-circuiting. Figure 1 In the example, the side reinforcement 60 is provided on the end surfaces of the positive electrode 20, the negative electrode 30 and the solid electrolyte layer 40 in the X direction and the Y direction. The material of the side reinforcement 60 is not particularly limited as long as it is an insulating material, for example, resin, glass, ceramic, etc.

[0043] As described above, the negative electrode 30 involved in this embodiment comprises: a negative electrode collector (negative electrode collector layer 31); a negative electrode active material layer 33; a first layer (anti-peeling layer 32), which is arranged between the negative electrode collector and the negative electrode active material layer 33; and a second layer (covering layer 34), which is arranged on the negative electrode active material layer 33, the negative electrode collector contains a negative electrode collector material, the negative electrode collector material is at least one metal of copper, nickel, and iron, the negative electrode active material layer 33 contains silicon, the first layer contains silicon, a metal element constituting the negative electrode 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.

[0044] Thus, even when the negative electrode active material layer 33 expands, the second layer can suppress cracking of the negative electrode active material layer 33 , and the first layer can suppress separation of the negative electrode current collector and the negative electrode active material layer 33 , thereby improving the cycle retention rate.

[0045] As a desirable aspect, the elements constituting the first layer other than silicon and the metal constituting the negative electrode current collector are the same as the elements constituting the second layer other than silicon. This can evenly relax the stress of the negative electrode 30 .

[0046] In a more preferred aspect, the element constituting the first layer other than silicon and the metal constituting the negative electrode current collector is titanium, and the element constituting the second layer other than silicon is titanium. This can reduce the resistance of the first layer and the second layer.

[0047] As a desired aspect, the concentration of silicon contained on the negative electrode active material layer side of the first layer is higher than the concentration of silicon contained on the negative electrode collector side of the first layer, the concentration of the negative electrode collector material contained on the negative electrode collector side of the first layer is higher than the concentration of the negative electrode collector material contained on the negative electrode active material layer 33 side of the first layer, and the second layer contains silicon in the entire thickness direction. As a result, the interface energy between the cap layer 34 and the negative electrode active material layer 33 can be further suppressed, and the interface resistance between the second layer and the negative electrode active material layer 33 can be further reduced. In addition, since the concentration of silicon in the first layer changes continuously in the direction where the negative electrode active material layer 33 is provided, the interface energy with the negative electrode active material layer 33 can be further suppressed, and the resistance between the negative electrode collector and the negative electrode active material layer 33 can be further reduced. In addition, since the concentration of the negative electrode collector material in the first layer changes continuously in the direction where the negative electrode collector is provided, the interface energy with the negative electrode collector can be further suppressed, and the resistance between the negative electrode collector and the negative electrode active material layer 33 can be further reduced.

[0048] The secondary battery 1 according to the present embodiment includes the positive electrode 20 , the negative electrode 30 , and an electrolyte (solid electrolyte layer 40 ). By adopting this configuration, the cycle retention rate can be improved.

[0049] (Method for manufacturing negative electrode)

[0050] The negative electrode 30 according to the present embodiment is produced, for example, by the following method.

[0051] First, as a stacking process, a first metal layer, a silicon-containing layer, and a second metal layer are stacked in sequence on the negative electrode collector layer 31. The stacking process is performed in a manner that is not in contact with air, for example, by stacking by sputtering, chemical vapor deposition, ion plating, or the like. The first metal layer is a layer composed of a first metal, and the thickness is greater than 0.1 μm and less than 1 μm. Here, the second metal layer is a layer composed of a second metal, and the thickness is greater than 0.1 μm and less than 1 μm. The silicon-containing layer is a layer composed of a material containing silicon, for example, a layer of a mixture of silicon and a dopant. In this case, mixing is performed by stacking silicon and a dopant simultaneously on the first metal layer.

[0052] Next, the stacked body including the negative electrode current collector layer 31 is annealed. By 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 such that silicon is included in the entire thickness direction of the cap layer 34. Here, the portion of the silicon-containing layer where the first metal or the second metal is not diffused becomes the negative electrode active material layer 33.

[0053] (Second embodiment)

[0054] Figure 2It is a schematic cross-sectional view showing an example of a secondary battery involved in the second embodiment. The secondary battery involved in this embodiment is described below. It should be noted that the same figure marks are marked on the same structure and the description is omitted. The difference between the secondary battery 1A involved in the second embodiment and the secondary battery 1 involved in the first embodiment and the second embodiment is that the negative electrode 30A has a plurality of negative electrode active material layers 33a~33d and a plurality of cover layers 34a~34d. Here, the cover layer 34a~34d is an example of a "second layer". Regarding the plurality of negative electrode active material layers 33a~33d, the thickness of each of the plurality of cover layers 34a~34d is smaller than the thickness of the anti-peeling layer 32.

[0055] like Figure 2 As shown, in the secondary battery 1A according to the second embodiment, the negative electrode active material layers 33a to 33d and the capping layers 34a to 34d are stacked in the order of negative electrode active material layer 33d, capping layer 34d, negative electrode active material layer 33c, capping layer 34c, negative electrode active material layer 33b, capping layer 34b, negative electrode active material layer 33a, and capping layer 34a in the +Z direction of the peeling prevention layer 32. That is, in the secondary battery 1A, it can be said that the capping layers 34a to 34d are alternately stacked with the negative electrode active material layers 33a to 33d in the Z direction.

[0056] By adopting this structure, the capping layers 34b to 34d can suppress the peeling of the negative electrode active material layers 33a to 33d from each other, thereby improving the cycle characteristics of the secondary battery 1A. In addition, the second metal contained in the capping layers 34b to 34d plays the role of a surfactant (surfactant) of the silicon-containing layer in the manufacture of the negative electrode 30A, so the silicon-containing layer can be thickened, thereby improving the capacity of the secondary battery 1. More specifically, in the manufacture of the negative electrode 30A, by stacking the second metal layer on the silicon-containing layer, the surface energy of the first silicon-containing layer is reduced, and the thickness of the second silicon-containing layer stacked on the second metal layer is promoted.

[0057] (Third Embodiment)

[0058] Figure 3 1 is a schematic cross-sectional view showing an example of a secondary battery according to the third embodiment. The secondary battery 100 according to the third embodiment is a cylindrical battery having a liquid electrolyte. Figure 3 As shown, the secondary battery 200 includes a housing 110, a positive electrode 120, a negative electrode 130, and a separator 150. The housing 110 is a shell that accommodates an electrode body and an electrolyte solution (not shown) inside. The housing 110 includes a battery can 111, a cover 112, a thermistor element 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.

[0059] The battery can 111 is a cylindrical member including an end surface that becomes a negative electrode of the secondary battery 100. That is, the battery can 111 is a cylinder with one end surface closed and the other end surface open. The battery can 111 is a conductor, for example, the surface of an iron (Fe) substrate is plated with nickel (Ni).

[0060] The cover 112 is a disc-shaped member including a protrusion that becomes the positive pole of the secondary battery 100. The cover 112 is provided on the end surface of the battery can 111 on the open side. The cover 112 is made of metal, for example, the same material as the battery can 111.

[0061] Here, in the description of this embodiment, the direction in which the cylindrical portion of the battery can 111 extends is sometimes described as the length direction of the secondary battery 100. In addition, the + pole of the secondary battery 100 refers to the protrusion of the cover 112, and the - pole of the secondary battery 100 refers to the closed end surface of the battery can 111.

[0062] The thermistor element 113 is an element whose resistance increases with a rise in temperature. The thermistor element 113 is provided on the negative electrode side of the cover 112. When the secondary battery 100 reaches a high temperature due to a short circuit or the like, the resistance value of the thermistor element 113 increases to limit the current.

[0063] The safety valve mechanism 114 is a mechanism whose shape changes according to the air pressure in the housing 110. The safety valve mechanism 114 is arranged on the -pole side relative to the thermistor element 113. The safety valve mechanism 114 is electrically connected to the cover 112 via the thermistor element 113. The safety valve mechanism 114 has a protrusion on the -pole side, and when the air pressure in the housing 110 is normal, the protrusion is connected to the positive lead 116 and electrically connected. On the other hand, when the air pressure in the housing 110 rises, the protrusion of the safety valve mechanism 114 flips to the +pole side and leaves the positive lead 116, thereby electrically disconnecting the positive lead 116 from the cover 112.

[0064] The gasket 115 is an annular component that fixes the cover 112, thermistor element 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 makes the battery can 111 and the cover 112 close together, making the inside of the housing 110 airtight. The gasket 115 is an insulator.

[0065] The positive electrode lead 116 is a terminal connected to a positive electrode 120 of an electrode assembly described below. The positive electrode lead 116 is electrically connected to the lid 112 via the safety valve mechanism 114 and the thermistor element 113. The positive electrode lead 116 is a conductor, such as aluminum (Al).

[0066] The negative electrode lead 117 is a terminal connected to a negative electrode 130 of an electrode body described below. 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).

[0067] The insulating plate 118 is a plate-shaped member serving as an insulator. Two insulating plates 118 are provided so as to cover each of a cross section of an electrode body described below on the positive electrode side of the secondary battery 100 and a cross section on the negative electrode side of the secondary battery 100 .

[0068] The center pin 119 is provided at the center 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 is, for example, metal.

[0069] Figure 4 yes Figure 3 A magnified view of area A. Figure 3 and Figure 4 As shown, 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 the battery can 111. Figure 3 In the example shown in FIG. 1 , the positive electrode 120 , the negative electrode 130 , and the separator 150 are stacked in a radial direction of the secondary battery 100 with the center pin 119 as the center.

[0070] The positive electrode 120 includes a positive electrode collector layer 121 and a positive electrode active material layer 122. In the positive electrode 120, the positive electrode collector layer 121 is stacked on two layers of positive electrode active material layers 122. The material and thickness of the positive electrode collector layer 121 are the same as those of the positive electrode collector layer 21 in the first embodiment. In addition, 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.

[0071] The negative electrode 130 includes a negative electrode collector layer 131 and a negative electrode material layer 132. Here, the negative electrode collector layer 131 is an example of a "negative electrode collector". In the negative electrode 130, the negative electrode collector layer 131 is stacked on two layers of negative electrode material layers 132. The negative electrode collector layer 131 is the same material as the negative electrode 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 an anti-peeling layer, a negative electrode active material layer and a capping layer of the same material as the first embodiment. That is, the anti-peeling layer is an example of a "first layer", and the capping layer is an example of a "second layer". Here, the capping layer is a layer thinner than the anti-peeling layer. The negative electrode material layer 132 is a laminated body obtained by stacking the anti-peeling layer, the negative electrode active material layer and the capping layer in order from the negative electrode collector layer 131 side. Thus, even if the negative electrode active material layer expands, the anti-peeling layer is provided, so that the negative electrode material layer 132 can be prevented from peeling off from the negative electrode collector layer 131. In addition, even if cracks are generated in the negative electrode active material layer due to expansion, the cover layer is provided, so that the electrolyte solution penetrates into the cracks and forms a film on the new surface in the cracks, which can prevent the negative electrode active material from deteriorating. Therefore, the cycle characteristics of the secondary battery 100 can be improved.

[0072] The separator 150 is a layer that insulates the positive electrode 120 from the negative electrode 130. The separator 150 is arranged so that the positive electrode 120 and the negative electrode 130 are not in direct contact, and is stacked between the positive electrode 120 and the negative electrode 130 in the electrode body. The material of the separator 150 is preferably electrically stable, chemically stable to the positive electrode active material, the negative electrode active material and the electrolyte, and insulating. For example, the separator 150 can use a layer composed of polymer non-woven fabrics, porous films, glass or ceramic fibers. More preferably, the material of the separator 150 includes a porous polyolefin film. In addition, the separator 150 can be composed of a plurality of layers, or a separator obtained by compounding a porous polyolefin film with a heat-resistant film containing polyimide, glass or ceramic fibers can be used.

[0073] 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, for example, lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO2C2F5)2), or lithium hexafluoroarsenate (LiAsF6) and other lithium salts. The solvent may be, for example, a lactone solvent such as γ-butyrolactone, γ-valerolactone, δ-valerolactone or ε-caprolactone; a carbonate solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate; an ether solvent such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, tetrahydrofuran or 2-methyltetrahydrofuran; a nitrile solvent such as acetonitrile; a cyclopentane solvent; a phosphoric acid or phosphate ester solvent; or a non-aqueous solvent including pyrrolidones or the like.

[0074] (Fourth Embodiment)

[0075] Figure 5 It is a cross-sectional view showing an example of a secondary battery according to a fourth embodiment. Figure 6 yes Figure 5 A schematic diagram of a cross section of line VI-VI of FIG. 4 shows a secondary battery 200 according to the fourth embodiment having a gel electrolyte. Figure 5 and Figure 6 As shown, the secondary battery 200 according to the fourth embodiment includes a battery element, an outer casing 211 , a sealing member 212 , a protective member 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 .

[0076] The outer packaging member 211 is the shell of the secondary battery 200. The outer packaging member 211 includes an insulating layer, a metal layer, and an outermost layer. The outer packaging member 211 is a structure obtained by laminating an insulating layer, a metal layer, and an outermost layer in sequence from the inside and bonding them together through lamination processing. The insulating layer of the outer packaging member 211 is composed of resins such as polyethylene, polypropylene, modified polyethylene, modified polypropylene, or polyolefin resins containing ethylene or propylene as monomers. As a result, the outer packaging member 211 can reduce the moisture permeability of the secondary battery 200 and improve the airtightness. The metal layer of the outer packaging member 211 is a plate or foil film composed of metals such as aluminum, stainless steel, nickel, or iron. The outermost layer can be made of any material, for example, it is preferably composed of a material with high strength against rupture, piercing, etc., such as the same resin as the insulating layer, nylon, etc.

[0077] The sealing member 212 is a member for making the outer packaging member 211 airtight. The sealing member 212 is provided between the outer packaging member 211 and the positive electrode lead 260 and the negative electrode lead 270. The material of the sealing member 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 metal, the sealing member 212 uses a polyolefin resin such as polyethylene, polypropylene, modified polyethylene or modified polypropylene. Thus, the gap between the outer packaging member 211 and the positive electrode lead 260 or the negative electrode lead 270 can be sealed, so that the inner part of the outer packaging member 211 can be made airtight.

[0078] The positive electrode 220 includes a positive electrode collector layer 221 and a positive electrode active material layer 222. The material and thickness of the positive electrode collector layer 221 are the same as those of the positive electrode collector layer 21 in the first embodiment. In addition, 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.

[0079] The negative electrode 230 includes a negative electrode collector layer 231 and a negative electrode material layer 232. Here, the negative electrode collector layer 131 is an example of a "negative electrode collector". The negative electrode collector layer 131 includes an anti-peeling layer, a negative electrode active material layer, and a capping layer of the same material as in the first embodiment. That is, the anti-peeling layer is an example of a "first layer", and the capping layer is an example of a "second layer". Here, the capping layer is a layer thinner than the anti-peeling layer. In addition, the negative electrode material layer 232 is the same as the negative electrode material layer 132 in the third embodiment, and is a laminate obtained by stacking an anti-peeling layer, a negative electrode active material layer, and a capping layer in sequence from the negative electrode collector layer 231 side. As a result, even if the negative electrode active material layer expands, since the anti-peeling layer is provided, it is possible to suppress the negative electrode material layer 132 from peeling off from the negative electrode collector layer 131. Furthermore, even if cracks are generated in the negative electrode active material layer due to expansion, the presence of the cap layer can suppress deterioration of the negative electrode active material due to the electrolyte gel entering the cracks. Thus, the cycle characteristics of the secondary battery 200 can be improved.

[0080] like Figure 6 As shown, 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, that is, the protective member 213 side, the negative electrode 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 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 stacked in this order.

[0081] The gel electrolyte layer 240 is a layer that becomes the electrolyte of the secondary battery 200. The gel electrolyte layer 240 is a gel-like layer composed of a polymer compound that retains an electrolyte. As long as the polymer compound used as the gel of the gel electrolyte layer 240 absorbs a solvent and gels, any polymer compound can be used. For example, fluorine-based polymer compounds such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene can be listed; ether-based polymer compounds such as polyethylene oxide or a cross-linked body containing polyethylene oxide; or polymer compounds containing polyacrylonitrile, polypropylene oxide or polymethyl methacrylate as monomers. 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. By adopting this material, the stability to the redox reaction can be improved. Here, the copolymer of the polymer compound used as the gel of the gel electrolyte layer 240 may further contain, as monomers, monoesters of unsaturated dibasic acids such as monomethyl maleate, halogenated vinyl such as chlorotrifluoroethylene, cyclic carbonates of unsaturated compounds such as vinyl carbonate, or epoxy-containing acrylic vinyl monomers. In this case, the cycle characteristics can be improved.

[0082] The positive electrode lead 260 is a terminal that is led out from the positive electrode current collector layer 221 to the outside of the outer casing 211. In other words, the positive electrode lead 260 is a terminal that serves as the positive electrode of the secondary battery 200. Figure 6 In the embodiment, the positive electrode lead 260 is provided near the center of the portion surrounded by the protective member 213. The material of the positive electrode lead 260 is the same as that of the positive electrode lead 116 in the third embodiment.

[0083] The negative electrode lead 270 is a terminal that is led out from the negative electrode current collector layer 231 to the outside of the outer casing 211. In other words, the negative electrode lead 270 is a terminal that becomes the negative electrode of the secondary battery 200. Figure 6 In the embodiment, the negative electrode lead 270 is provided near the center of the portion surrounded by the protective member 213. The material of the negative electrode lead 270 is the same as that of the positive electrode lead 116 in the third embodiment.

[0084] The protective member 213 is a member for protecting the secondary battery 200. The protective member 213 is provided so as to be wound around the negative electrode 230. The protective member 213 is, for example, a tape of an insulator.

[0085] The embodiments described above are for facilitating understanding of the present disclosure and are not intended to be interpreted in a limiting manner. The present disclosure may be modified / improved without departing from the gist thereof, and equivalents thereof are also included in the present disclosure.

[0086] Description of Reference Numerals

[0087] 1, 1A: secondary battery; 10: protective layer; 20: positive electrode; 21: positive electrode collector layer; 22: positive electrode active material layer; 30, 30A: negative electrode; 31: negative electrode collector layer; 32: anti-peeling layer; 33, 33a~33d: negative electrode active material layer; 34, 34a~34d: cover layer; 40: solid electrolyte layer; 50: insulating layer; 60: side reinforcement; 100: secondary battery; 110: outer shell; 111: battery can; 112: cover; 113: thermistor element; 114: safety valve mechanism; 115: gasket; 116: positive electrode lead; 117: negative electrode lead; 11 8: insulating plate; 119: center pin; 120: positive electrode; 121: positive electrode collector layer; 122: positive electrode active material layer; 130: negative electrode; 131: negative electrode collector layer; 132: negative electrode material layer; 150: diaphragm; 200: secondary battery; 211: outer packaging member; 212: sealing member; 213: protective member; 220: positive electrode; 221: positive electrode collector layer; 222: positive electrode active material layer; 230: negative electrode; 231: negative electrode collector layer; 232: negative electrode material layer; 240: gel electrolyte layer; 250: diaphragm; 260: positive electrode lead; 270: negative electrode lead.

Claims

1. A negative electrode having: A negative electrode current collector; A negative electrode active material layer; A first layer is provided between the negative electrode current collector and the negative electrode active material layer; and The second layer is provided on the negative electrode active material layer, The negative electrode current collector comprises at least one of copper, nickel and iron. The negative electrode active material layer includes silicon, The first layer includes 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 includes silicon and at least one of titanium, nickel, zinc, silver, iron, boron, indium, and germanium.

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

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

4. The negative electrode according to any one of claims 1 to 3, wherein The concentration of silicon contained in the first layer on the negative electrode active material layer side is higher than the concentration of silicon contained in the first layer on the negative electrode current collector side. The concentration of the metal constituting the negative electrode collector contained in the negative electrode collector side of the first layer is higher than the concentration of the metal constituting the negative electrode collector contained in the negative electrode active material layer side of the first layer, The second layer includes silicon throughout the thickness direction. 5 . A secondary battery comprising the negative electrode according to claim 1 , a positive electrode, and an electrolyte.

Images