JP2021034143A - Electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and current collector to use in electrode for nonaqueous electrolyte secondary battery - Google Patents

Abstract

To provide an electrode for a nonaqueous electrolyte secondary battery, which can prevent the occurrence of liquid depletion in which an electrolyte solution runs out to achieve a long life and a high energy density.SOLUTION: An electrode 3 for a nonaqueous electrolyte secondary battery comprises: an electrically conductive current collector 30; an active material layer 31 fixed to the current collector 30 and containing an active material; and a porous layer 32 disposed adjacent to the active material layer 31. The current collector 30 is composed of a three dimensional structure having many pores. The active material layer 31 is formed on the current collector 30 so as to have many pores which enable the absorption and releasing of an electrolyte solution. The porous layer 32 contains an elastically deformable material having many pores which enable the absorption and releasing of the electrolyte solution, and has a porosity higher than that of the active material layer 31.SELECTED DRAWING: Figure 2

Description

The present invention relates to a current collector for use as an electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and an electrode for a non-aqueous electrolyte secondary battery.

In recent years, secondary batteries have been used in various products. There is a demand from the market for a secondary battery having a long life, high output, and high energy density. As a secondary battery of this type, a non-aqueous electrolyte secondary battery represented by a lithium ion battery is known. In order to achieve high energy density, for example, as much active material as possible is filled per unit volume (or per unit mass) of the electrode, and as the negative electrode active material, it is alloyed with lithium instead of the graphite-based material. For example, it has been proposed to use a silicon (Si) -based material.

JP-A-2010-153140 Japanese Unexamined Patent Publication No. 2017-21888 JP-A-2018-113108

As the amount of active material filled in the electrode increases, the amount of change in the volume of the electrode also increases in proportion to the amount. For example, when a material that alloys with lithium ions during charging is used as the negative electrode active material, the volume expands remarkably with the alloying. For example, in the case of a Si-based material, its volume expands about four times. That is, in such a secondary battery, the active material layer expands and contracts significantly with charging and discharging.

Expansion and contraction of the active material layer causes destruction of the active material particles, damage at the interface between the current collector and the active material layer, and so-called "dripping" in which the electrolytic solution is insufficient between the electrodes and between the active material layers. Tends to invite. The dripping hinders the smooth movement of ions, which causes a decrease in battery capacity and an increase in internal resistance.

The present invention has been devised in view of the above problems, and is an electrode for a non-aqueous electrolyte secondary battery capable of preventing the occurrence of dripping, achieving a long life, and achieving a high energy density. The main issue is to provide such as.

The present invention is an electrode for a non-aqueous electrolyte secondary battery, which is adjacent to a conductive current collector, an active material layer containing an active material fixed to the current collector, and the active material layer. The current collector is a three-dimensional structure having a large number of pores, and the active material layer has a large number of pores capable of absorbing and releasing an electrolytic solution. The void layer is formed of a current collector and is made of an elastically deformable material having a large number of pores capable of absorbing and releasing an electrolytic solution, and has a void ratio higher than the void ratio of the active material layer. Have.

In another aspect of the present invention, the void layer may have an elastic skeleton capable of shrinking and deforming so that the volume of its large number of holes is reduced.

In another aspect of the present invention, the void layer may have an elastic skeleton that can be contracted and deformed so that its apparent volume is reduced when the active material layer receives an external force when it is expanded and deformed. ..

In another aspect of the present invention, the active material layer may be formed on both sides of the void layer.

In another aspect of the present invention, the porosity of the active material layer in the carrier-releasing state may be in the range of 5% to 50%.

In another aspect of the present invention, the porosity of the void layer in the carrier-releasing state may be in the range of 40% to 80%.

In another aspect of the present invention, the void layer may be made of a non-woven fabric of metal fibers.

In another aspect of the present invention, the material of the metal fiber may be stainless steel.

In another aspect of the present invention, the fiber diameter of the metal fiber may be 12 μm or less.

In another aspect of the present invention, the current collector comprises adjacently comprising a first layer formed using a first metal fiber and a second layer formed using a second metal fiber. The active material layer is formed in the first layer, the second layer is the void layer that does not contain the active material, and the fiber diameter of the second metal fiber is that of the first metal fiber. It may be configured to be smaller than the fiber diameter.

In another aspect of the present invention, the fiber diameter of the second metal fiber may be 1 μm or more, and the fiber diameter of the first metal fiber may be 5 μm or more.

In another aspect of the present invention, the non-woven fabric may be further coated with a metal composed of any of copper, nickel, chromium and titanium transition metal elements, or an alloy containing these transition metal elements as a main component. good.

In another aspect of the present invention, the active material may be a material containing silicon.

In another aspect of the present invention, the active material layer may be a layer of a mixture containing the active material and a binder, or a layer of a mixture containing the active material and a solid electrolyte.

In another aspect of the present invention, the void layer of the electrode according to any one of the above may be configured as a non-aqueous electrolyte secondary battery in which an electrolytic solution is filled.

In another aspect of the present invention, as a non-aqueous electrolyte secondary battery, when charging or discharging, the void layer has its own apparent volume when it receives an external force when the active material layer expands and deforms. It may have an elastic skeleton that can be contracted and deformed so as to be reduced.

In another aspect of the present invention, the non-aqueous electrolyte secondary battery may include a solid electrolyte or a gel electrolyte between the positive electrode and the negative electrode.

In another aspect of the present invention, a lithium ion may be used as a carrier as a non-aqueous electrolyte secondary battery.

In another aspect of the present invention, an assembled battery using the non-aqueous electrolyte secondary battery described in any of the above may be used.

In another aspect of the present invention, it may be an electric device using the above-mentioned assembled battery.

In another aspect of the present invention, it is a current collector for use as an electrode for a non-aqueous electrolyte secondary battery, and is composed of a structure having conductivity and having a large number of holes. , A first layer for fixing the active material and a second layer capable of absorbing and releasing the electrolytic solution are contained adjacent to each other, and the second layer may have a higher porosity than the first layer. good.

In another aspect of the present invention, the first layer may be provided on both sides of the second layer.

In another aspect of the present invention, the first layer is formed by using a first metal fiber, and the second layer uses a second metal fiber having a fiber diameter smaller than that of the first metal fiber. May be formed.

In another aspect of the present invention, the first layer is formed using the first metal fiber.
The second layer may be formed by using a second metal fiber having an elastic modulus smaller than that of the first metal fiber.

In the present invention, the current collector is composed of a three-dimensional structure having a large number of holes, unlike the conventional foil materials. Further, the active material layer is formed in the current collector so as to have a large number of pores capable of absorbing and releasing the electrolytic solution. Therefore, the current collector has a large surface area and can fix many active materials three-dimensionally. This helps to provide secondary batteries with higher energy and output densities.

Further, in the present invention, a void layer is arranged adjacent to the active material layer. This void layer is made of an elastically deformable material having a large number of pores capable of absorbing and releasing an electrolytic solution. Further, the void layer has a porosity higher than the porosity of the active material layer. Therefore, when the active material layer is expanded and deformed, the void layer can elastically contract and supply the electrolytic solution held by itself to the adjacent active material layer. Therefore, the shortage of the electrolytic solution in the active material layer is suppressed. On the contrary, when the active material layer is contracted and deformed, the void layer is restored to its original shape, and the excess electrolytic solution for the contracted active material layer is recovered. In this way, the electrolytic solution is exchanged between the active material layer and the void layer according to the expansion / contraction form of the active material layer, so that the active material layer or the active material layer or Liquid dripping between the electrodes is suppressed.

The term "elasticity" means a property in which a member deformed by an external force tends to return to its original shape when the external force is removed. Therefore, elasticity is a word that expresses properties, and is not an index that is expressed numerically. However, many members have elasticity while the applied force is small, but it is known that when the force increases beyond a certain limit, the deformation cannot be restored even if the force is removed. In the present application, the optimum elastic modulus changes depending on the type of active material that expands and contracts with charge and discharge. Therefore, at least an elastically deformable material that can exhibit the effects of the present invention may be used. Further, the "elastic skeleton" in the present application refers to a skeleton that uses the above-mentioned elastically deformable material as a skeleton or exhibits elasticity derived from a basic structure.

Further, in a foil-shaped current collector, damage such as cracks is likely to occur in the active material layer or at the interface between the active material layer and the current collector due to repeated expansion and contraction deformation of the active material layer due to charging and discharging. Tend. On the other hand, in the present invention, the stress generated by the expansion / contraction deformation of the active material layer is relaxed by propagating to the adjacent void layer. Therefore, in the present invention, damage such as internal cracks in the electrode is suppressed, and the life can be extended.

It is a schematic schematic diagram of the non-aqueous electrolyte secondary battery of one Embodiment of this invention. It is an enlarged schematic diagram of a negative electrode. It is a schematic diagram which shows the expanded state of the negative electrode active material of FIG. It is a schematic diagram which shows the state which the negative electrode active material of FIG. 2 has shrunk. It is a schematic diagram explaining the negative electrode current collector. It is a schematic diagram explaining the positive electrode. It is a 300 times enlarged cross-sectional photograph which shows an example of an active material layer and a void layer. It is a photograph which shows the state of the negative electrode of the comparative example after a cycle test. It is a photograph which shows the state of the negative electrode of an Example after a cycle test.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings do not always match the dimensional ratio of the actual structure, but rather may be exaggerated. Further, the same or common elements are given the same reference numerals, and duplicate explanations are omitted. Furthermore, the specific configurations shown in the embodiments and drawings are for understanding the contents of the present invention, and the present invention is not limited to the specific configurations shown.

[Overall structure of secondary battery]
FIG. 1 shows a schematic view of a lithium ion secondary battery having a lithium ion as a carrier as a non-aqueous electrolyte secondary battery (hereinafter, simply referred to as “secondary battery”) 1 to which one embodiment of the present invention is applied. Shown.

As shown in FIG. 1, the secondary battery 1 includes a positive electrode 2, a negative electrode 3, and a separator 4 arranged between them, and these are built in the casing 5. The secondary battery 1 has a set of a positive electrode 2 and a negative electrode 3 as one unit, and the number of units is adjusted according to the required voltage. Each positive electrode 2 is connected to a positive electrode terminal 7 outside the battery via a lead 6. Similarly, each negative electrode 3 is connected to the negative electrode terminal 9 outside the battery via the lead 8. Although not shown, the positive electrode 2, the separator 4, and the negative electrode 3 in the casing 5 are all impregnated with a non-aqueous electrolytic solution. Hereinafter, these components will be described in detail.

[casing]
The casing 5 is an exterior body for accommodating the positive electrode 2, the negative electrode 3, the separator 4, and the electrolytic solution of the secondary battery, and is a container having a so-called outer shape of the battery. The casing material is not particularly limited, but stainless steel, which is resistant to corrosion by chemicals and has mechanical strength, is suitable. In another aspect, as the casing material, in addition to the surface-treated iron-based material, a laminated film made of an aluminum-based material or a resin may be adopted if mechanical strength is not required.

[Separator]
The separator 4 is a diaphragm arranged between the positive electrode 2 and the negative electrode 3 in order to prevent direct contact with the negative electrode 3. The separator 4 is composed of, for example, a porous membrane provided with a plurality of micropores so that lithium ions in the electrolytic solution can move between the positive electrode 2 and the negative electrode 3. As such a separator 4, for example, a resin such as polypropylene or polyethylene, a non-metallic inorganic material such as glass, or the like is used.

[Electrolytic solution]
The electrolyte is the medium required for the movement of lithium ions. In the region where the electrolytic solution is insufficient or depleted (that is, the liquid is drained), lithium ions cannot move, which hinders charging and discharging. In the lithium ion battery, for example, an organic electrolytic solution in which a lithium salt is dissolved is adopted as the electrolytic solution. As the electrolyte constituting the non-aqueous electrolyte solution, known electrolytes such as lithium trifluoromethanesulfonylamide (Li-TFSA) and lithium hexafluorophosphate (LiPF ₆ ) can be used. As the solvent for the non-aqueous electrolyte solution, for example, known solvents for non-aqueous solvent-based secondary batteries such as carbonate (ethylene carbonate, diethyl carbonate, etc.), ether (tetraglime, etc.), nitrile, and sulfur-containing compounds are adopted. Can be done.

[Negative electrode]
FIG. 2 shows an enlarged view of the negative electrode 3 of FIG. 1 as an example of the electrode. As shown in FIG. 2, the negative electrode 3 includes a conductive current collector (hereinafter, referred to as “negative electrode current collector”) 30 and an active material fixed to the negative electrode current collector 30 (hereinafter, “negative electrode”). It includes an active material layer (hereinafter, referred to as “negative electrode active material layer”) 31 containing (referred to as “active material”) and a void layer 32 arranged adjacent to the negative electrode active material layer 31.

[Negative electrode current collector]
In the present embodiment, the negative electrode current collector 30 is composed of a three-dimensional structure having a large number of holes. Tertiary structure includes any structural element that forms a large number of holes regularly and / or irregularly. In a preferred embodiment, the three-dimensional structure includes a large number of contiguous holes that irregularly traverse the interior of the current collector so that it has high liquid permeability. Since such a negative electrode current collector 30 has a large surface area as compared with a foil material having the same apparent volume, more active materials can be three-dimensionally fixed. Such a negative electrode current collector 30 serves to provide a secondary battery with a higher energy density and output density.

As the material of the negative electrode current collector 30 as described above, for example, a metal fiber non-woven fabric such as stainless steel is suitable. The metal fiber non-woven fabric entangles the metal fibers three-dimensionally by applying heat or mechanical pressure (for example, pressing, sintering, needle punching, etc.) to a large number of metal fibers having no specific orientation. It is a cloth material that has been made. Details of suitable metal fiber non-woven fabrics will be described later.

[Negative electrode active material layer]
The negative electrode active material layer 31 contains a negative electrode active material. The negative electrode active material is a reducing agent for the purpose of transmitting and receiving electrons, and various materials can be used. Examples of the negative electrode active material include graphite-based materials and lithium-titanium-based materials. Further, the negative electrode active material may be a material that alloys with lithium, for example, a silicon (Si) -based material, in order to increase the capacity and energy density of the secondary battery. Materials to be alloyed with lithium include aluminum (Al), silver (Ag), bismuth (Bi), gallium (Ga), germanium (Ge), silicon (Si), tin (Sn), antimony (Sb), and lead. Examples thereof include a simple substance selected from (Pb), an alloy containing these as a main component, an oxide, a chalcogen compound, a halide and the like. These negative electrode active materials may be used alone or in combination of two or more.

The negative electrode active material layer 31 is formed in the negative electrode current collector 30 so as to have a large number of holes capable of absorbing and discharging the electrolytic solution. The negative electrode active material layer 31 of the present embodiment completely fills the holes of the negative electrode current collector 30 of the three-dimensional structure with, for example, a mixture of the negative electrode active material and an additive such as a conductive auxiliary agent or a binder. It is formed by applying and curing without any need. As a result, the negative electrode active material layer 31 of the present embodiment is fixed to the negative electrode current collector 30 having a three-dimensional structure (mesh structure) having a large number of holes capable of absorbing and discharging the electrolytic solution.

The conductive auxiliary agent is a material used for forming the electrodes (positive electrode 2, negative electrode 3) of a secondary battery for the purpose of reducing the resistance of charge transfer between active material particles, and more macroscopically, the internal resistance of the electrodes. Is. As the conductive auxiliary agent, for example, acetylene black, carbon black, vapor-grown carbon fiber (VGCF), or the like can be adopted.

The binder is a binder for fixing the active material, the conductive auxiliary agent, and other additives to the negative electrode current collector 30. As the binder, for example, a thermoplastic fluoropolymer such as polyvinylidene chloride, a rubber polymer such as styrene-butadiene rubber (SBR), a polyimide resin, or the like can be adopted.

The mixture may further contain a solid electrolyte or a gel electrolyte. According to this configuration, when the electrolyte interposed between the positive electrode and the negative electrode is a solid electrolyte or a gel electrolyte, the ionic conductivity of the active material layer can be improved to obtain a battery having excellent input / output characteristics. it can. Those with an transport rate close to 1 such as solid electrolytes can move carriers efficiently. Further, when a solid electrolyte, a polymer electrolyte, or the like is used, the separator may be omitted. Further, the presence of the electrolytic solution makes it possible to repair breakage of the solid electrolyte or the like.

In one aspect of the secondary battery 1 of the present embodiment, a solid electrolyte or a gel electrolyte may be provided between the positive electrode 2 and the negative electrode 3. According to this configuration, a battery in which a solid electrolyte or a gel electrolyte is interposed between the positive electrode and the negative electrode and the electrode contains an electrolytic solution is provided. A general electrolyte is a liquid that is easily flammable, but a solid electrolyte or a gel electrolyte tends to be less flammable than this. Therefore, in this aspect, it is possible to construct a battery that does not easily catch fire while maintaining good ionic conductivity due to the electrolytic solution.

Further, according to the battery having this configuration, the electrolytic solution held by the electrode due to the volume change of the active material layer due to charge / discharge is supplied to the solid electrolyte or the gel electrolyte interposed between the positive electrode and the negative electrode. It becomes possible. Therefore, the larger the volume change of the active material layer is, the larger the supply amount of the electrolytic solution is. Therefore, even in a battery using an electrolyte having poor fluidity between the positive electrode and the negative electrode, it is possible to easily secure ionic conductivity. Further, by interposing a solid electrolyte or a gel electrolyte between the positive electrode and the negative electrode, the amount of the electrolytic solution used in the battery can be reduced, and it can be expected that the battery exhibits excellent safety. ..

In the present embodiment, the negative electrode active material layers 31 are formed on both sides of the void layer 32, respectively. In another aspect, the negative electrode active material layer 31 may be formed on only one side of the void layer 32.

[Void layer]
The void layer 32 is a layer for filling the electrolytic solution. The void layer 32 of the present embodiment is made of a material that has a large number of pores capable of absorbing and releasing an electrolytic solution and is elastically deformable. Like the negative electrode current collector 30, the void layer 32 of the present embodiment is made of a metal fiber non-woven fabric made of a material such as stainless steel. The metal fiber non-woven fabric forms a large number of continuous holes regularly and / or irregularly from the surface to the inside. The void layer 32 can hold the electrolytic solution in these pores.

In the present embodiment, the void layer 32 is used in a state where the metal fiber non-woven fabric is not coated with the mixture essentially containing the negative electrode active material. Therefore, a boundary 40 is formed between the negative electrode active material layer 31 and the void layer 32.

Since the void layer 32 is made of an elastically deformable material, it has, for example, an elastic skeleton that can be contracted and deformed so as to reduce the volume of the holes inside the void layer 32 when an external force is applied. In the present specification, the "apparent volume" is a volume calculated from the external dimensions of the target portion.

Further, in the present embodiment, the porosity of the void layer 32 is formed higher than the porosity of the negative electrode active material layer 31. In the present specification, the "porosity" is the ratio of the space volume to the apparent volume of the target portion, and the porosity of the void layer 32 is the void ratio of the negative electrode active material layer 31 according to the following equation (1). The rates are calculated by the following equations (2), respectively.
Porosity (%) of the void layer
= (Spatial volume) / (Apparent volume of void layer) x 100 ... (1)
Porosity (%) of the negative electrode active material layer
= {(Apparent volume of negative electrode active material layer)-(Volume of negative electrode current collector)-(Volume of mixture containing negative electrode active material)} / (Apparent volume of negative electrode active material layer) x 100 ... (2)

In the negative electrode 3 configured as described above, as shown in FIG. 3, the negative electrode active material layer 31 occludes lithium ions and expands and deforms during charging. Along with this expansion, the void layer 32 adjacent to the negative electrode active material layer 31 elastically contracts by receiving an external force from the negative electrode active material layer 31, and releases the electrolytic solution held by itself. The electrolytic solution released by the void layer 32 is supplied to the adjacent negative electrode active material layer 31. Therefore, the shortage of the electrolytic solution around the negative electrode active material layer 31 is suppressed.

On the contrary, as shown in FIG. 4, at the time of discharge, the negative electrode active material layer 31 contracts and deforms by releasing lithium ions. Along with this shrinkage deformation, the void layer 32 adjacent to the negative electrode active material layer 31 elastically restores to its original shape, and the electrolytic solution surplus for the shrunk negative electrode active material layer 31 is placed in its own pores. It can be recovered. In addition, the elastic restoration of the void layer 32 suppresses the formation of a gap at the boundary 40 between the void layer 32 and the negative electrode active material layer 31. As a result, dripping is further suppressed.

In this way, the necessary electrolytic solution is exchanged between the negative electrode active material layer 31 and the void layer 32 according to the deformation form of the expansion / contraction of the negative electrode active material layer 31. Therefore, according to the electrode (negative electrode 3) of the present embodiment, between the negative electrode active material layer 31 and / or the electrodes (positive electrode 2 and negative electrode 3) without excessively filling the electrode with an electrolytic solution in advance. It is possible to suppress dripping. Such an advantage is particularly useful when the amount of change in expansion of the negative electrode active material layer 31 is large, that is, when a material alloying with lithium is used as the negative electrode active material.

In addition, in foil-shaped current collectors that have been widely used so far, cracks occur in the active material layer or at the interface between the active material layer and the current collector due to the deformation of repeated expansion and contraction of the active material layer due to charging and discharging. There was a tendency for damage such as, etc. to occur easily. On the other hand, in the present embodiment, the stress generated by the deformation of the expansion / contraction of the negative electrode active material layer 31 is alleviated by propagating to the adjacent void layer 32 as well. Therefore, in the electrode of the present embodiment, it is possible to damage the internal cracks and the like of the electrode and extend the life of the electrode.

As described above, the void layer 32 has a function of holding the electrolytic solution and supplying it to the negative electrode active material layer 31 when necessary (electrolyte solution holding function), and a negative electrode active material layer 31 by its own elastic shape restoration. It has a function of restoring the shape before charging (shape restoration function) and a buffer function against a volume change of the negative electrode active material layer 31. In order to realize such a function more effectively, the porosity of the void layer 32 in the carrier discharge state (state in which the battery is discharged) is preferably 40% to 80%, more preferably 60% to 80. It is in the range of%.

When the porosity of the negative electrode active material layer 31 is less than 5%, there is an advantage that a larger amount of active material can be secured in the layer, but the volume change at the time of expansion and deformation of the negative electrode active material layer 31 cannot be buffered, and charging and discharging cannot be performed. That is, it causes cracks due to repeated expansion and contraction, detachment and peeling of the active material layer, and the like. On the other hand, if the porosity of the negative electrode active material layer 31 is 60% or more, a sufficient amount of active material may not be secured in the layer. Therefore, in order to provide a sufficient surface area of the negative electrode active material layer 31 while holding the electrolytic solution, the porosity in the carrier discharge state (state in which the battery is discharged) is in the range of 5% to 50%. Is desirable.

In a preferred embodiment, the void layer 32 is made of a non-woven fabric of metal fibers made of stainless steel. The type of stainless steel is not particularly limited, but austenitic stainless steel having excellent corrosion resistance, weldability, workability, etc. is preferable, and SUS316L is particularly preferable.

In another aspect, a metal fiber made of copper, nickel, chromium, titanium or an alloy thereof may be applied to the void layer 32.

The fiber diameter of the metal fibers constituting the void layer 32 is preferably 12 μm or less, for example. By thinning the fiber diameter in this way, it is possible to easily form a large number of holes capable of absorbing and releasing the electrolytic solution. Further, it is useful for lowering the rigidity of the void layer 32 and, by extension, enhancing its cushioning function. The fiber diameter of the metal fiber is preferably 1 μm or more, for example, in consideration of the durability of the void layer 32 and the like.

In a preferred embodiment, the negative electrode current collector 30 for fixing the negative electrode active material layer 31 is a first layer 310 formed by using the first metal fiber 311 and a second metal fiber, as shown in FIG. It is made of a non-woven fabric provided with a second layer 320 formed by using 321 adjacent to the second layer 320. The first layer 310 and the second layer 320 may be integrally formed in advance, or may be formed separately and then laminated with each other. In the embodiment of FIG. 5, as a preferred example, the first layer 310 is formed on both sides of the second layer 320.

In a preferred embodiment, the fiber diameter of the second metal fiber 321 is configured to be smaller than the fiber diameter of the first metal fiber 311. Then, the first layer 310 is formed as the negative electrode active material layer 31 (shown in FIG. 2) by applying and curing the mixture containing the negative electrode active material. Further, the second layer 320 is formed as a void layer 32 (shown in FIG. 2) by not applying the mixture.

In such an embodiment, the second layer 320 constituting the void layer 32 has a lower rigidity than the first layer 310 for fixing the negative electrode active material layer 31. Therefore, the void layer 32 can exhibit an excellent buffering function when the negative electrode active material layer 31 is expanded and deformed.

The fiber diameter of the second metal fiber 321 is preferably 1 μm or more, and more preferably 2 μm or more. As described above, the upper limit of the fiber diameter of the second metal fiber 321 is preferably 12 μm or less.

The fiber diameter of the first metal fiber 311 is preferably 5 μm or more, and more preferably 7 μm or more. The upper limit of the fiber diameter of the first metal fiber 311 is preferably 20 μm or less, for example. As described above, in the first layer 310 using the relatively thick first metal fiber 311, the plastic deformation due to the large expansion and contraction of the negative electrode active material layer 31 is suppressed, and the elastic deformation function of the negative electrode active material layer 31 is maintained. Helps to do.

In a preferred embodiment, in the negative electrode current collector 30, the second layer 320 may be configured to have a higher porosity than the first layer 310. Such a second layer 320 can hold a relatively large amount of electrolytic solution as compared with the negative electrode active material layer 31. Further, when the negative electrode active material layer 31 is expanded and deformed, the void layer 32 that exhibits an excellent buffering function is formed.

In a preferred embodiment, the second metal fiber 321 constituting the second layer 320 may be configured to have a smaller elastic modulus than the first metal fiber 311 constituting the first layer 310. Such a second layer 320 flexibly deforms to follow the expansion / contraction deformation of the negative electrode active material layer 31 to form a void layer 32 exhibiting an excellent buffering function.

Further, the negative electrode current collector 30 may be further coated with a metal composed of any transition metal element such as copper, nickel, chromium or titanium, or an alloy containing these transition metal elements as main components. By coating with such a metal, it becomes a current collector having excellent conductivity while being a negative electrode current collector having an elastic deformation function, and an electrode using this becomes a current collector without metal coating, as compared with a current collector without metal coating. The resistance value of the ohmic component becomes low.

[Positive electrode]
As an example of the electrode of the secondary battery 1, the negative electrode 3 has been described in detail so far, but the configuration of the negative electrode 3 may be similarly applied to the positive electrode 2. Although the positive electrode 2 has a smaller volume change during charging and discharging than the negative electrode 3, volume expansion occurs due to occlusion of lithium ions during discharging. Therefore, the configuration described for the negative electrode may be applied to the positive electrode 2. ..

FIG. 6 shows a partially enlarged view of the positive electrode 2 as described above. As shown in FIG. 6, the positive electrode 2 includes a conductive current collector (hereinafter, referred to as “positive electrode current collector”) 20 and an active material fixed to the positive electrode current collector 20 (hereinafter, “positive electrode”). It includes an active material layer (hereinafter, referred to as “positive electrode active material layer”) 21 containing (referred to as “active material”) and a void layer 22 arranged adjacent to the positive electrode active material layer 21. Here, the positive electrode current collector 20 and the void layer 22 have the same configurations as the negative electrode current collector 30 and the void layer 32, respectively, and the repeated description is omitted here.

The positive electrode active material is an oxidizing agent for the purpose of transferring ions to and from the positive electrode 2. For example, a powdered active material mixed with a conductive auxiliary agent, a binder, or the like and compacted is used. Be done. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO ₂ ), lithium iron phosphate (LiFePO ₄ ), a ternary material (Li (Ni, Co, Mn) O ₂ ) and the like are suitable. Further, the positive electrode active material may be a material that absorbs carriers and exhibits a large volume change, for example, a sulfur-based material, a silicate-based material, or a vanadium-based material, in order to increase the capacity and energy density of the secondary battery. .. In addition, these positive electrode active materials may be used individually by 1 type or in combination of 2 or more types. When used as a positive electrode, the void layer 22 is preferably made of a non-woven fabric of metal fibers made of stainless steel. In another aspect, a metal fiber made of aluminum or an alloy thereof may be applied to the void layer 22.

[Battery set]
A plurality of secondary batteries (single batteries) 1 configured as described above may be connected to form an assembled battery (not shown). The shape and connection method of the assembled battery can be appropriately designed according to the application. Such an assembled battery is suitably used, for example, as a motor power source for an electric vehicle or a hybrid vehicle that requires high energy density and high capacity.

[Electrical equipment]
The secondary battery 1 of the present embodiment or various electric devices incorporating the assembled battery can be configured. Examples of such electric devices include, but are not limited to, electric vehicles, hybrid vehicles, mobile phones, smartphones, computers, power storage equipment, and the like.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned specific disclosure, and is various within the scope of the technical idea described in the claims. It can be changed and implemented. Further, in the above embodiment, the lithium ion secondary battery has been described as an example, but the present invention describes, for example, a sodium ion secondary battery, a potassium ion secondary battery, a magnesium ion secondary battery, an aluminum ion secondary battery, and the like. It is also applicable to non-aqueous electrolyte secondary batteries. In addition, some of the embodiments disclosed herein can be implemented independently or combined with each other.

In order to confirm the effect of the present invention, three types of secondary batteries (Comparative Examples, Examples 1 and 2) were prototyped, and constant current charge / discharge tests were carried out for each.

In the secondary battery of the comparative example, a stainless steel foil was used as the negative electrode current collector.

On the other hand, the configuration of the negative electrode of the secondary battery of the embodiment is as shown in FIG. As shown in FIG. 7, the negative electrode 3 is composed of a void layer 32 and a pair of negative electrode active material layers 31 formed on both sides thereof. The negative electrode active material layer 31 is fixed to the negative electrode current collector. In this example, a stainless steel (SUS316L) metal fiber non-woven fabric is used for both the negative electrode current collector and the void layer.

Silicon monoxide (SiO, particle diameter 2-3 μm, carbon coating on particle surface (SiO: carbon (C) = 99: 1 (% by weight))) as negative electrode active material, acetylene black (AB, denka) as conductive aid , Denka Black), polyimide precursor (polyamic acid) as a binder was weighed at a ratio of 85: 5: 15 (% by weight), and self-revolving using N-methyl-2-pyrrolidone (NMP) as a solvent. A negative electrode slurry was prepared by kneading using a formula mixer (Sinky Co., Ltd., ARE-310).

Next, in the examples, the obtained negative electrode slurry was filled in a non-woven fabric of stainless steel metal fibers (fiber diameter φ5.6 μm or 9.2 μm). In the comparative example, the negative electrode slurry was applied to both sides of a stainless steel metal foil (thickness 10 μm). Next, Examples and Comparative Examples were heat-treated in a vacuum at 240 ° C. for 10 hours using a vacuum dryer. The area where the negative electrode active material layer was formed was 5 cm × 5 cm.

Using each of the obtained electrodes as a test electrode, metallic lithium (thickness 500 μm) was used as the counter electrode, a glass filter (Advantech, GA-100) and a polyolefin-based microporous membrane were used as the separator, and 1M LiPF ₆ EC (ethylene carbonate) was used as the electrolytic solution. A laminated battery was produced by using DEC (diethyl carbonate) (= 1/1, v / v) and an aluminum laminated film as an exterior material. A constant current charge / discharge test was carried out for each of the manufactured batteries, with an environmental temperature of 30 ° C., a charge / discharge rate of 0.1 C rate, and a voltage range of 0.01-1.2 V. The discharge capacity retention rate was adopted as the evaluation of the charge / discharge test. The discharge capacity retention rate represents the ratio of the 10th, 20th, and 40th discharge capacities to the case where the 4th discharge capacity is 100%. The larger the value, the better. The test results are shown in Table 1.

As is clear from Table 1, it was confirmed that in Examples 1 and 2, the decrease in discharge capacity was suppressed as compared with Comparative Examples.

After the test, each battery was disassembled and the state of each negative electrode was visually observed. As a result of observation, as shown in FIG. 8, the negative electrode of the comparative example had wrinkles, deformations, and cracks, and peeling of the negative electrode active material layer from the negative electrode current collector was also confirmed (the whitish pattern in the figure is confirmed). Shows wrinkles and cracks). It is presumed that this is due to the volume expansion and contraction of about four times that of the negative electrode active material layer during charging. On the other hand, in the negative electrode of Example 1, as shown in FIG. 9, no wrinkles, deformations, cracks, or peeling of the active material layer from the current collector could be confirmed on the electrodes.

1 Non-aqueous electrolyte secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 5 Casing 20 Positive electrode current collector 21 Positive electrode active material layer 22 Void layer 30 Negative electrode current collector 31 Negative electrode active material layer 22, 32 Void layer 310 First layer 311 First Metal fiber 320 Second layer 321 Second metal fiber

Claims (24)

Electrodes for non-aqueous electrolyte secondary batteries
With a conductive current collector,
An active material layer containing an active material fixed to the current collector, and
Including a void layer arranged adjacent to the active material layer,
The current collector is a three-dimensional structure having a large number of holes.
The active material layer is formed in the current collector so as to have a large number of pores capable of absorbing and releasing the electrolytic solution.
The void layer is made of an elastically deformable material having a large number of pores capable of absorbing and releasing an electrolytic solution, and has a porosity higher than the porosity of the active material layer.
Electrodes for non-aqueous electrolyte secondary batteries. The electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the void layer has an elastic skeleton that can be contracted and deformed so that the volume of a large number of pores is reduced. The non-aqueous electrolyte according to claim 1 or 2, wherein the void layer has an elastic skeleton that can be contracted and deformed so as to reduce its own apparent volume when the active material layer receives an external force when it expands and deforms. Electrodes for secondary batteries. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the active material layer is formed on both sides of the void layer. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the porosity of the active material layer in the carrier-releasing state is in the range of 5% to 50%. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the porosity of the void layer in the carrier-releasing state is in the range of 40% to 80%. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the void layer is made of a non-woven fabric of metal fibers. The electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the material of the metal fiber is stainless steel. The electrode for a non-aqueous electrolyte secondary battery according to claim 7 or 8, wherein the metal fiber has a fiber diameter of 12 μm or less. The current collector includes a first layer formed by using the first metal fiber and a second layer formed by using the second metal fiber adjacent to each other.
The active material layer is formed in the first layer.
The second layer is the void layer that does not contain the active material.
The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 9, wherein the fiber diameter of the second metal fiber is smaller than the fiber diameter of the first metal fiber. The electrode for a non-aqueous electrolyte secondary battery according to claim 10, wherein the second metal fiber has a fiber diameter of 1 μm or more and the first metal fiber has a fiber diameter of 5 μm or more. Any of claims 7 to 11, wherein the non-woven fabric is further coated with a metal composed of any of copper, nickel, chromium, and titanium as a transition metal element, or an alloy containing these transition metal elements as a main component. The electrode for a non-aqueous electrolyte secondary battery according to item 1. The electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 12, wherein the active material is a material containing silicon. The non-water-free layer according to any one of claims 1 to 13, wherein the active material layer is a layer of a mixture containing the active material and a binder, or a layer of a mixture containing the active material and a solid electrolyte. Electrode for electrolyte secondary batteries. A non-aqueous electrolyte secondary battery in which the void layer of the electrode according to any one of claims 1 to 14 is filled with an electrolytic solution. 15. The void layer has an elastic skeleton that can be contracted and deformed so as to reduce its own apparent volume when the active material layer receives an external force when the active material layer is expanded and deformed during charging or discharging. The non-aqueous electrolyte secondary battery described. The non-aqueous electrolyte secondary battery according to claim 15 or 16, wherein a solid electrolyte or a gel electrolyte is provided between the positive electrode and the negative electrode. The non-aqueous electrolyte secondary battery according to any one of claims 15 to 17, wherein the carrier is lithium ion. An assembled battery using the non-aqueous electrolyte secondary battery according to any one of claims 15 to 18. An electric device using an assembled battery using the non-aqueous electrolyte secondary battery according to claim 19. A current collector for use as an electrode for a non-aqueous electrolyte secondary battery.
It is composed of a structure having conductivity and having a large number of holes, and the structure is adjacent to a first layer for fixing an active material and a second layer capable of absorbing and releasing an electrolytic solution. Including
The second layer has a higher porosity than the first layer.
Current collector. The current collector according to claim 21, wherein the first layer is provided on both sides of the second layer. The first layer is formed by using the first metal fiber, and is formed.
The current collector according to claim 21 or 22, wherein the second layer is formed by using a second metal fiber having a fiber diameter smaller than that of the first metal fiber. The first layer is formed by using the first metal fiber, and is formed.
The current collector according to any one of claims 21 to 23, wherein the second layer is formed by using a second metal fiber having an elastic modulus smaller than that of the first metal fiber.