JP2023098028A - Current collector, electrode for power storage device, lithium ion secondary battery, and method for manufacturing current collector - Google Patents

Abstract

To provide a current collector having excellent resistance to a non-aqueous electrolyte, an electrode for a power storage device, a lithium ion secondary battery, and a method for manufacturing such a current collector.SOLUTION: A current collector includes a resin layer, a conductive layer, and an intermediate layer positioned between the resin layer and the conductive layer, the conductive layer includes Al or Cu as a main component, and the intermediate layer includes Mo as the main component.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present disclosure relates to current collectors, electrodes for power storage devices, lithium ion secondary batteries, and methods for manufacturing current collectors.

As a current collector for a secondary battery, it has been proposed to use a composite material in which a conductive layer is formed on one or both sides of a resin film. Patent Literature 1 discloses a current collector for a secondary battery in which such a composite material is applied to the current collector.

JP 2019-102429 A

When the current collector of the composite material described above is used in an electricity storage device having a non-aqueous electrolyte such as a lithium ion secondary battery, the current collector is expected to have high resistance to the non-aqueous electrolyte. preferable. An embodiment of the present disclosure provides a current collector with excellent resistance to non-aqueous electrolyte, an electrode for a power storage device, a lithium ion secondary battery, and a method for manufacturing such a current collector.

A current collector according to an embodiment of the present disclosure includes a resin layer, a conductive layer, and an intermediate layer positioned between the resin layer and the conductive layer, wherein the conductive layer is mainly made of Al or Cu. As a component, the intermediate layer contains Mo as a main component.

Further, a method for manufacturing a current collector according to an embodiment of the present disclosure includes steps of preparing a resin layer, forming an intermediate layer containing Mo as a main component on the resin layer, forming Al on the intermediate layer, Alternatively, a step of forming a conductive layer containing Cu as a main component.

According to one embodiment of the present disclosure, a current collector, an electrode for a power storage device, and a lithium ion secondary battery having excellent resistance to non-aqueous electrolytes are provided.

FIG. 1 is a schematic cross-sectional view showing an example of a current collector according to the first embodiment. FIG. 2 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross section of the intermediate layer when the intermediate layer contains molybdenum oxide. FIG. 3 is a flow chart showing the current collector manufacturing method according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing an example of the current collector of the second embodiment. FIG. 5 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross section of the intermediate layer. FIG. 6 is a schematic cross-sectional view showing another example of the current collector of the second embodiment. FIG. 7 is a schematic exploded perspective view showing an example of the electricity storage device electrode of the third embodiment. FIG. 8 is a schematic partially cutaway perspective view showing an example of the lithium ion secondary battery of the fourth embodiment. 9 is a schematic exploded perspective view showing an example of a cell of the lithium ion secondary battery shown in FIG. 8. FIG.

A current collector in which a conductive layer is formed on a resin film differs from a metal foil conventionally used as a single current collector in terms of structure and thickness. In particular, the conductive layer is supported by a resin film and is thinner than the metal foil used in conventional current collectors, which is different from conventional current collectors.

A lithium ion secondary battery generally includes a non-aqueous electrolyte containing an anion containing a fluorine atom as an electrolyte, and when the above-described current collector is used in a lithium ion secondary battery, must have good tolerance. For example, when such a lithium ion secondary battery is charged and discharged in a high-temperature environment, anions containing fluorine atoms are decomposed to produce fluorine ions, ie, hydrofluoric acid, as a decomposition product. The inventor of the present application aims to suppress deterioration of a current collector in which a conductive layer is formed on a resin film due to decomposition products of a non-aqueous electrolyte, specifically, to suppress peeling of the conductive layer from the resin film. As a result, the present inventors have devised a current collector, an electrode for a power storage device, and a lithium ion secondary battery that can suppress deterioration of the current collector and maintain charge/discharge characteristics.

Hereinafter, embodiments of a current collector, an electrode for a power storage device, and a lithium ion secondary battery of the present disclosure will be described with reference to the drawings. Numerical values, shapes, materials, steps, order of the steps, etc. presented in the following description are merely examples, and various modifications are possible as long as there is no technical contradiction. Also, each embodiment described below is merely an example, and various combinations are possible as long as there is no technical contradiction.

The thickness, size, shape, etc. of members shown in the drawings of this disclosure may be exaggerated for convenience of explanation. Also, in the drawings of this disclosure, some members may be isolated and some elements may be omitted to avoid undue complexity. As such, the respective dimensions and inter-member placement of the members depicted in the drawings of this disclosure may not reflect the respective dimensions and inter-member placement of the members in the actual device. "Perpendicular" and "perpendicular" in the present disclosure are not limited to two straight lines, sides, surfaces, etc. forming an angle of 90 °, but include cases in the range of about ± 5 ° from 90 ° . Also, "parallel" includes cases where two straight lines, sides, surfaces, etc. are in the range of about 0° to ±5°.

As used herein, the term "cell" refers to an integrally assembled structure of at least one pair of positive and negative electrodes. The term "battery" as used herein is used as an umbrella term for various forms such as battery modules, battery packs, etc., having one or more "cells" electrically connected to each other.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing an example of the current collector of this embodiment. The current collector of the present embodiment can be used as a current collector for both positive and negative electrodes of an electricity storage device such as a lithium ion secondary battery. Current collector 101 includes resin layer 10 , conductive layer 20 , and intermediate layer 30 positioned between resin layer 10 and conductive layer 20 .

The resin layer 10 functions as a support for the conductive layer 20 in the current collector 101 . In addition, the resin layer 10 has a density lower than that of the conductive layer 20, so that it can contribute to increasing the charging capacity per unit weight when an electricity storage device is configured.

The resin layer 10 has electrical insulation and contains resin. The resin layer 10 may have thermoplasticity. Specifically, the resin layer 10 is made of polyethylene terephthalate (PET), polypropylene (PP), polyamide (PA), polyimide (PI), polyethylene (PE), polystyrene (PS), phenol resin (PF) and epoxy resin ( EP) may be included. The resin layer 10 may be a single layer, or may be configured by laminating two or more layers. In this case, at least one of the layers may contain a resin different from that of the other layers.

The thickness of the resin layer 10 is, for example, 3 μm or more and 12 μm or less. The thickness of the resin layer 10 may be 3 μm or more and 6 μm or less. By setting the thickness of the resin layer 10 to 3 μm or more, sufficient strength as a support can be obtained. Further, by setting the thickness of the resin layer 10 to 12 μm or less, the thickness of the current collector 101 as a whole can be reduced. Therefore, when a laminated lithium ion secondary battery is constructed by laminating a plurality of electrode pairs, the proportion of the current collector, which does not contribute to energy storage, can be reduced, and the energy density can be increased. If the thickness of the resin layer 10 is 6 μm or less, the thickness of the current collector 101 as a whole can be made smaller, and the energy density of the laminated lithium ion secondary battery can be increased.

Current collector 101 may further include an undercoat layer positioned between resin layer 10 and intermediate layer 30 . The undercoat layer can be provided to increase the bonding strength between the resin layer 10 and the intermediate layer 30 or to suppress the formation of pinholes in the intermediate layer 30 . For example, the undercoat layer may be a layer formed from an organic material such as acrylic resin or polyolefin, or a metal-containing layer formed by a sputtering method.

The intermediate layer 30 has the function of increasing the adhesion between the resin layer 10 and the conductive layer 20 in the non-aqueous electrolyte and suppressing the separation of the conductive layer 20 from the resin layer 10 . The intermediate layer 30 contains Mo as a main component. The term "main component" as used herein refers to the element that contains the largest percentage of the constituent elements in mole percent when the member contains one or more constituent elements. However, when the content of oxygen (O) is the highest, it refers to the element with the next highest content, excluding oxygen. Also, the content ratio of the constituent elements can be determined, for example, by performing line analysis of the constituent elements on a cross section parallel to the thickness direction of the intermediate layer 30 with a scanning transmission electron microscope (STEM). Preferably, the intermediate layer 30 contains only Mo as the metal element, excluding unavoidable impurity elements.

Although the detailed reason is not clear, the inclusion of Mo in the intermediate layer 30 suppresses the peeling of the conductive layer 20 from the resin layer 10 when the current collector is held in the non-aqueous electrolytic solution. In particular, peeling of the conductive layer 20 from the resin layer 10 is suppressed even when fluorine ions, which are considered to be generated when the lithium ion secondary battery is charged and discharged at high temperature, are present in the non-aqueous electrolyte.

In the intermediate layer 30, Mo contained as a main component may be oxidized. That is, the intermediate layer 30 may contain molybdenum oxide. Since molybdenum oxide has polarity, the inclusion of molybdenum oxide in the intermediate layer 30 enhances the interaction with the resin layer 10, which tends to have polarity due to its molecular structure, at the interface between the intermediate layer 30 and the resin layer 10. , the adhesion is further improved. The oxidation number of Mo in the molybdenum oxide may be +4, +6, or other oxidation numbers. Moreover, Mo with a different oxidation number may be included. Alternatively, the intermediate layer 30 may be a single layer of molybdenum oxide made entirely of molybdenum oxide.

For the reason described above, when the intermediate layer 30 contains molybdenum oxide, it is preferable that the molybdenum oxide is mostly contained on the resin layer 10 side in the thickness direction of the intermediate layer 30 . More preferably, molybdenum oxide is located on lower surface 30 b of intermediate layer 30 that contacts resin layer 10 .

FIG. 2 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross section of the intermediate layer 30 when the intermediate layer 30 contains molybdenum oxide. In FIG. 2 , the horizontal axis indicates the distance, and the origin is positioned at the interface between the intermediate layer 30 and the conductive layer 20 , that is, the upper surface 30 a of the intermediate layer 30 . The vertical axis in FIG. 2 indicates the amount of constituent elements. Such a distribution of constituent elements in the thickness direction of the cross section of the intermediate layer 30 can be obtained, for example, by subjecting the cross section of the intermediate layer 30 to energy dispersive X-ray spectroscopy (STEM-EDX) using a scanning transmission electron microscope. In this case, the vertical axis is the X-ray count or intensity.

As shown in FIG. 2, when the intermediate layer 30 contains molybdenum oxide, for example, in the profile of the constituent elements in the thickness direction of the cross section of the intermediate layer 30, the O peak position P1 is higher than the Mo peak position P2 in the resin layer. Located on the 10th side. By having such a profile, adhesion to the resin layer 10 can be further enhanced at the lower surface 30b of the intermediate layer 30 as described above. On the other hand, since the concentration of Mo is high on the conductive layer 20 side of the intermediate layer 30 , the intermediate layer 30 on the conductive layer 20 side has enhanced properties as a metal and improved adhesion to the conductive layer 20 .

The distribution profile of the constituent elements shown in FIG. 2 is an example, and O and Mo may be distributed according to another profile. For example, in the intermediate layer 30, the concentration or abundance of O (count or intensity in the case of a STEM-EDX profile) may increase stepwise or continuously from the upper surface 30a to the lower surface 30b. In this case, the concentration or abundance of Mo may decrease stepwise or continuously from the upper surface 30a toward the lower surface 30b. Even if the intermediate layer 30 has such a profile, the adhesion between the upper surface 30a and the conductive layer 20 and the adhesion between the lower surface 30b and the resin layer 10 can be enhanced.

After forming the intermediate layer 30, if the conductive layer 20 is formed in a film forming apparatus different from the film forming apparatus in which the intermediate layer 30 is formed, the surface of the intermediate layer 30 is exposed to the atmosphere before the conductive layer 20 is formed. may be In this case, the upper surface 30a of the intermediate layer 30 may be oxidized by oxygen in the atmosphere. Even in this case, it is preferable that a large amount of molybdenum oxide is contained on the resin layer 10 side in the thickness direction of the intermediate layer 30 .

The thickness d2 of the intermediate layer 30 is, for example, 1 nm or more and less than 200 nm. If the thickness d2 of the intermediate layer 30 is 1 nm or more, a continuous film can be formed, and the adhesion can be improved over the entire region between the conductive layer 20 and the resin layer 10 . When the thickness d2 of the intermediate layer 30 is less than 200 nm, the time required to form the intermediate layer 30 does not become too long, and the resin layer 10 is protected from damage due to conditions during the formation of the intermediate layer 30, such as heat and plasma. The influence on the resin layer 10 is reduced, and the deterioration of the resin layer 10 can be suppressed.

Damage to the resin layer 10 caused by heat or plasma includes, for example, wrinkles on the surface of the resin layer 10 . When such wrinkles occur in the resin layer 10 , the unevenness of the wrinkles is also reflected in the intermediate layer 30 and the conductive layer 20 . As a result, when the active material layer is formed on the conductive layer 20 by coating, the thickness of the active material layer becomes uneven. That is, when the thickness d2 of the intermediate layer 30 is less than 200 nm, wrinkling of the intermediate layer 30 is suppressed, and an active material layer having a uniform thickness can be easily formed on the current collector.

The thickness d2 of the intermediate layer 30 may be 6 nm or more and 100 nm or less. If the thickness d2 of the intermediate layer 30 is 6 nm or more, the adhesion between the conductive layer 20 and the resin layer 10 can be enhanced more reliably. Further, by setting the thickness d2 of the intermediate layer 30 to 100 nm or less, the above-described damage to the intermediate layer 30 can be further suppressed.

The intermediate layer 30 may contain other metals as long as it contains Mo as a main component. The intermediate layer 30 can be formed using known thin film forming techniques used in the manufacture of semiconductor devices, such as a vacuum deposition method and a sputtering method.

The conductive layer 20 is a main current path in the current collector 101, and transfers electrons between a positive electrode active material or a negative electrode active material and a terminal or the like connected to the current collector. The conductive layer 20 contains metal as a main component.

Conductive layer 20 contains Al or Cu as a main component. As long as it contains Al or Cu as a main component, it may further contain other metals. For example, the conductive layer 20 may contain Cu as a main component and may further contain Ni. When current collector 101 is used as a positive electrode, conductive layer 20 may contain Al. When current collector 101 is used as a negative electrode, conductive layer 20 may contain Cu or a Ni—Cu alloy.

The thickness d1 of the conductive layer 20 is, for example, 0.3 μm or more and 3 μm or less. By setting the thickness d1 of the conductive layer 20 to 0.3 μm or more, the resistance of the conductive layer 20 can be reduced. For example, energy loss due to resistance in a current collector can be reduced when an electricity storage device is produced. In addition, since the thickness of the conductive layer 20 is 3 μm or less, the ratio of the conductive layer 20 to the resin layer 10 is relatively small, and there is an advantage that the weight of the current collector can be reduced by using the resin layer 10 . more likely to be The thickness of the conductive layer 20 may be 0.5 μm or more and 1.2 μm or less.

If conductive layer 20 is relatively thick, conductive layer 20 may include, for example, seed layer 21 and main layer 22 . The seed layer 21 and the main layer 22 each contain a metal as a main component, and may be made of the same metal.

The seed layer 21 is formed by, for example, sputtering or vacuum deposition, and the main layer 22 is formed by plating. As a result, forming the entire conductive layer 20 by a sputtering method or a vacuum deposition method lengthens the formation time, lowers productivity, and increases damage to the resin layer 10 during the formation of the conductive layer 20. can be avoided. When the conductive layer 20 includes the seed layer 21 and the main layer 22, the total thickness of the seed layer 21 and the main layer 22 preferably satisfies the value of the preferred conductive layer thickness d1 described above.

On the other hand, if the conductive layer 20 is relatively thin, it may be a single layer film formed entirely by the same method. For example, the entire conductive layer 20 may be formed by sputtering or vacuum deposition. Alternatively, the intermediate layer 30 may be used as a base layer for plating, and the entire conductive layer 20 may be formed by plating.

As described above, according to the current collector of the present embodiment, the intermediate layer 30 containing Mo as a main component is arranged between the resin layer 10 and the conductive layer 20, so that the conductive layer 20 and the resin layer 10 Adhesion is enhanced. Therefore, even when fluorine ions, which are considered to be generated when the lithium ion secondary battery is charged and discharged at high temperature, are present in the non-aqueous electrolyte, the conductive layer 20 is prevented from peeling off from the resin layer 10 in the current collector. be done.

Next, a method for manufacturing the current collector of this embodiment will be described. FIG. 3 is a flow chart showing the method for manufacturing the current collector of this embodiment. The current collector manufacturing method of the present embodiment includes a step S1 of preparing a resin layer, a step S2 of forming an intermediate layer, and a step S3 of forming a conductive layer. Each step will be described in detail below.

(1) Step S1 of preparing a resin layer
First, the resin layer 10 made of the material described above and having the thickness described above is prepared. The resin layer 10 may have, for example, a size corresponding to the current collector 101 used in one lithium-ion secondary battery, or may be formed by winding a sheet-like resin layer long in one direction into a roll. It may be a resin roll. If the current collector is to be produced as it is without cutting the resin roll, a manufacturing facility capable of manufacturing by a roll-to-roll method is prepared.

(2) Step S2 of forming an intermediate layer
An intermediate layer 30 is formed by a sputtering method. A target containing Mo is prepared, and an intermediate layer 30 is formed on the resin layer 10 using a sputtering device. The thickness of the intermediate layer 30 can be adjusted by the film formation rate and film formation time. When forming the intermediate layer 30 substantially free of molybdenum oxide, for example, a Mo target of 3N or more is used, and the intermediate layer 30 is formed in an argon atmosphere.

When forming the intermediate layer 30 containing molybdenum oxide, sputtering may be performed using a target containing molybdenum oxide, or sputtering may be performed using a Mo target in an atmosphere containing oxygen gas. good too. Further, by changing the oxygen gas concentration in the atmosphere during the formation of the intermediate layer 30, the oxygen (O) content in the thickness direction of the intermediate layer 30 can be changed. For example, sputtering is started in an atmosphere containing oxygen gas at a first concentration, and the oxygen gas concentration is reduced stepwise or continuously from the first concentration. It is possible to form an intermediate layer with a low O content on the side.

(3) Step S3 of forming a conductive layer
A conductive layer 20 is formed on the intermediate layer 30 . For example, a conductive layer 20 containing Cu as its main component is formed. First, the seed layer 21 is formed on the intermediate layer 30 by sputtering, for example. Subsequently, the main layer 22 is formed on the seed layer 21 by electroplating using the seed layer 21 as a cathode. Thereby, the conductive layer 20 including the seed layer 21 and the main layer 22 can be formed.

When forming the conductive layer 20 containing Al as a main component, the conductive layer 20 including only the main layer 22 may be formed by a sputtering method or a vacuum deposition method.

(Second embodiment)
FIG. 4 is a schematic cross-sectional view showing an example of the current collector of this embodiment. The current collector 102 of this embodiment includes a resin layer 10, a conductive layer 20, and an intermediate layer 33, and the intermediate layer 33 has a first sub-intermediate layer 31 and a second sub-intermediate layer 32. is different from the current collector 101 of the first embodiment. As shown in FIG. 4, the first sub-intermediate layer 31 is closer to the resin layer 10 than the second sub-intermediate layer 32, and the second sub-intermediate layer 32 is closer to the conductive layer than the first sub-intermediate layer 31 is. Close to 20.

The first sub-intermediate layer 31 and the second sub-intermediate layer 32 are made of the same material as the intermediate layer 30 described in the first embodiment. However, the O content in the first sub-intermediate layer 31 is higher than the O content in the second sub-intermediate layer 32 . Here, when comparing the O content in the first sub-intermediate layer 31 and the second sub-intermediate layer 32, the average value of the O content in each layer in the thickness direction is used.

FIG. 5 is an example of a schematic profile showing the distribution of constituent elements in the thickness direction of the cross section of the intermediate layer 33 . As in the first embodiment, in FIG. 5 , the horizontal axis indicates distance, and the origin is positioned at the interface between the intermediate layer 33 and the conductive layer 20 . The vertical axis indicates the amount of constituent elements. Even in the profile of constituent elements by line analysis of STEM-EDX, the X-ray count or intensity shows similar changes with respect to distance.

As shown in FIG. 5, in the profile of the constituent elements in the thickness direction of the cross section of the intermediate layer 33, the O peak position P3 is positioned closer to the resin layer 10 than the Mo peak position P4. Preferably, the O peak position P3 is located within the first sub-intermediate layer 31 and the Mo peak position P4 is located within the second sub-intermediate layer 32 . By having such a profile, the adhesion between the lower surface 33b of the intermediate layer 33, that is, the first sub-intermediate layer 31 and the resin layer 10 can be further enhanced. On the other hand, the adhesion between the upper surface 33a of the intermediate layer 33, that is, the second sub-intermediate layer 32 and the conductive layer 20 is improved.

The thickness d3 of the first sub-intermediate layer 31 is, for example, 1 nm or more and 100 nm or less. Also, the thickness d4 of the second sub-intermediate layer 32 is, for example, 1 nm or more and 100 nm or less. The total thickness of the thickness d3 of the first sub-intermediate layer 31 and the thickness d4 of the second sub-intermediate layer 32 is preferably less than 200 nm. When the thickness d3 of the first sub-intermediate layer 31 and the thickness d4 of the second sub-intermediate layer 32 are each 1 nm or more, each layer can be easily formed as a continuous film. Therefore, the effect of improving adhesion between the resin layer 10 and the first sub-intermediate layer 31 and between the conductive layer 20 and the second sub-intermediate layer 32 can be easily obtained. In addition, since the thickness d3 of the first sub-intermediate layer 31 and the thickness d4 of the second sub-intermediate layer 32 are both 100 nm or less, damage to the resin layer 10 due to heat or the like can be further suppressed. The thickness d4 of the second sub-intermediate layer 32 is preferably larger than the thickness d3 of the first sub-intermediate layer 31 (d3<d4). Since the second sub-intermediate layer 32, which has higher metallic properties, is thicker than the first sub-intermediate layer 31, the strength of the entire intermediate layer 33 can be increased.

The current collector 102 can also be produced by a method similar to that for the current collector 101 of the first embodiment. When fabricating the current collector 102 , an intermediate layer 33 is formed instead of the intermediate layer 30 . That is, in step S2 of forming the intermediate layer described above, the first sub-intermediate layer 31 and the second sub-intermediate layer 32 are formed. For example, using a Mo target, the first sub-intermediate layer 31 is formed in an atmosphere containing oxygen at a first concentration, and the second sub-intermediate layer 32 is formed in an atmosphere containing oxygen at a second concentration lower than the first concentration. Form. Thereby, intermediate layer 33 including first sub-intermediate layer 31 and second sub-intermediate layer 32 is formed.

According to the current collector 101 of the present embodiment, since the intermediate layer 33 containing Mo as a main component is arranged between the resin layer 10 and the conductive layer 20, adhesion between the conductive layer 20 and the resin layer 10 is improved. sexuality is enhanced. In particular, since the intermediate layer 33 includes the first sub-intermediate layer 31 and the second sub-intermediate layer 32, adhesion between the intermediate layer 33 and the resin layer 10 and between the intermediate layer 33 and the conductive layer 20 is improved. It is possible to further improve the performance. Therefore, even when fluorine ions, which are considered to be generated when a lithium ion secondary battery is charged and discharged at high temperature, are present in the non-aqueous electrolyte, the conductive layer 20 can be separated from the resin layer 10 in the current collector. more restrained.

The current collector 101 described with reference to FIG. 1 and the current collector 102 described with reference to FIG. may be provided. For example, FIG. 6 shows a current collector 103 with conductive layers on both sides of a resin layer. The current collector 103 includes a resin layer 10 having a first surface 10a and a second surface 10b opposite to the first surface 10a. A structure similar to that of the current collector 102 described above is formed on the first surface 10a of the resin layer 10 .

On the other hand, a structure similar to that of the current collector 102 is also formed on the second surface 10 b of the resin layer 10 . Specifically, the current collector 103 further comprises a conductive layer 20' and an intermediate layer 33' including a first sub-intermediate layer 31' and a second sub-intermediate layer 32'. The first sub-intermediate layer 31' is located between the resin layer 10 and the second sub-intermediate layer 32'. The second sub-intermediate layer 32' is located between the first sub-intermediate layer 31' and the conductive layer 20'. The materials and thicknesses constituting the conductive layer 20', the first sub-intermediate layer 31' and the second sub-intermediate layer 32', the functions of these layers, etc. are described in the corresponding conductive layer 20, first sub-intermediate layer 31 and It is the same as the second sub intermediate layer 32 . In terms of stress, the material and thickness of the first sub-intermediate layer 31' and the second sub-intermediate layer 32' are similar to the material and thickness of the corresponding first sub-intermediate layer 31 and second sub-intermediate layer 32. may be the same as The material forming the conductive layer 20 ′ is the same as the material forming the corresponding conductive layer 20 . From a stress point of view, the thickness of conductive layer 20 ′ may be the same as the thickness of conductive layer 20 .

According to the current collector 103, since the conductive layers 20 and 20' are provided on both sides of the resin layer 10, electrodes can be formed on both sides. Therefore, the proportion of the resin layer in the electricity storage device can be reduced, and the battery capacity per unit area can be increased.

(Third embodiment)
An embodiment of an electrode for a power storage device will be described. The electricity storage device electrode of the present embodiment can be used for both the positive electrode and the negative electrode of the electricity storage device. FIG. 7 is an exploded perspective view of the electricity storage device electrode 201. FIG. The electricity storage device electrode 201 includes a current collector 210 and an active material layer 220 . Current collector 210 includes a first portion 210s and a second portion 210t, and active material layer 220 is disposed on first portion 210s. The second portion 210t is not provided with the active material layer 220 and functions as a tab for electrical connection to the outside. Active material layer 220 includes an active material that is oxidized and reduced during charging (or storage) and discharging. Current collector 210 supports active material layer 220 , supplies electrons to active material layer 220 , and receives electrons from active material layer 220 .

The current collector 210 is any one of the current collectors 101, 102, and 103 described in the first embodiment or the second embodiment. When the current collector 103 is used, another active material layer not shown in FIG. 7 is arranged on the first portion 210s on the back side of the current collector 210 (the side where the active material layer 220 is not arranged). .

Active material layer 220 includes a positive electrode active material or a negative electrode active material that absorbs and releases lithium ions. The positive electrode active material includes, for example, a composite metal oxide containing lithium. Examples of lithium-containing composite metal oxides include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound (LiV ₂ O ₅ ), olivine-type LiMPO ₄ (where M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr, or vanadium oxide), titanic acid Lithium ( _Li4Ti5O12 ) _, general formula: LiNixCoyMnzMaO2 ( _x + _y + _z +a _{= 1} , 0≤x<1, 0≤y< ₁ , 0≤z<1, 0≤a< 1, M in the above general formula is one or more elements selected from the group consisting of Al, Mg, Nb, Ti, Cu, Zn, and Cr), and a composite metal oxide represented by the general formula: LiNi Composite metal oxides represented by _x Co _y Al _z O ₂ (0.9<x+y+z<1.1) and the like can be mentioned. The positive electrode active material may contain polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, etc., as materials capable of intercalating and deintercalating lithium ions.

Active material layer 220 may further contain at least one of a binder and a conductive aid. Various known materials can be used for the binder. Binders in the active material layer 220 used for the positive electrode include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether. Fluorine such as copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) and polyvinyl fluoride (PVF) Resin can be used.

A vinylidene fluoride-based fluororubber may be used as the binder. For example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP-TFE-based fluororubber), vinylidene fluoride- Pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetra Fluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), etc. are applied to the binder of the active material layer 220 used for the positive electrode. good too.

Examples of conductive aids are carbon materials such as carbon powder and carbon nanotubes. Carbon black or the like can be applied to the carbon powder. Other examples of the conductive aid for the active material layer 220 used for the positive electrode are metal powders such as nickel, stainless steel and iron, and powders of conductive oxides such as ITO. Two or more of the above materials may be mixed and contained in the active material layer 220 .

The negative electrode active material contains a carbon material. Examples of carbon materials include natural or artificial graphite, carbon nanotubes, non-graphitizable carbon, easily graphitizable carbon (soft carbon), low-temperature fired carbon, and the like. The negative electrode active material may contain materials other than the carbon material. For example, alkali metals such as metallic lithium and alkaline earth metals, metals such as tin that can form compounds with metals such as lithium, silicon, silicon-carbon composites, amorphous compounds mainly composed of oxides (SiO _x (0<x<2), tin dioxide, etc.), lithium titanate (Li ₄ Ti ₅ O ₁₂ ), and other particles may be included.

As the binder and conductive aid of the active material layer 220 used for the negative electrode, the binder and conductive aid described above can be used in the same manner. Cellulose, styrene/butadiene rubber, ethylene/propylene rubber, polyimide, polyamideimide, acrylic resin, or the like may also be used as a binder for the negative electrode.

The positive electrode and negative electrode for an electric storage device can be manufactured by a known manufacturing method.

In the electricity storage device electrode of the present embodiment, the adhesion between the resin layer of the current collector and the conductive layer is enhanced. For this reason, even when the lithium ion secondary battery including the electricity storage device electrode of the present embodiment is used under conditions that facilitate decomposition of the electrolyte, for example, when the lithium ion secondary battery is used at high temperatures, the conductive layer is peeled off from the resin layer. This further suppresses deterioration of battery characteristics due to deterioration of the current collector.

(Fourth embodiment)
An embodiment of a lithium ion secondary battery will be described.

FIG. 8 is a schematic external view showing an example of the lithium ion secondary battery 301, and FIG. 9 is an exploded perspective view showing cells in the lithium ion secondary battery shown in FIG. Here, as a lithium ion secondary battery, a pouch type or laminated type lithium ion secondary battery is exemplified. The illustrated lithium ion secondary battery is of a single layer type, but may be of a laminated type. In the illustrated example, the positive electrode, separator, and negative electrode that constitute the cell are stacked along the Z direction in the figure.

A lithium ion secondary battery 301 includes a cell 310 , a pair of leads 311 connected to the cell 310 , an exterior body 313 covering the cell 310 , and an electrolyte 314 .

The cell 310 includes an electricity storage device electrode 201, an electricity storage device electrode 201', and a separator 320 disposed therebetween. In the illustrated example, cell 310 is a single layer cell that includes a pair of electrodes.

The power storage device electrode 201 and the power storage device electrode 201′ are the power storage device electrode 201 described in the third embodiment, one of which is a positive electrode containing a positive electrode active material, and the other is a negative electrode containing a negative electrode active material. It is configured.

Separator 320 is an insulating porous material. For example, a monolayer or laminated film of polyolefin such as polyethylene and polypropylene, or at least one fiber selected from the group consisting of cellulose, polyester, polyacrylonitrile, polyimide, polyamide (e.g. aromatic polyamide), polyethylene and polypropylene Nonwoven fabrics, porous films, and the like can be used.

An electrolyte 314 is further arranged in the space inside the exterior body 313 . The electrolyte 314 is a non-aqueous electrolyte containing lithium ions, such as a non-aqueous electrolytic solution containing lithium ions. When a non-aqueous electrolyte is applied to the electrolyte 314, a sealing material (for example, a resin film such as polypropylene) is typically placed between the outer casing 313 and the lead 311 to prevent leakage of the non-aqueous electrolyte. , not shown in FIG. 8) are arranged.

As the electrolyte 314, for example, a nonaqueous electrolytic solution containing a metal salt such as a lithium salt and an organic solvent can be used. Lithium _salts include, _for example, _LiPF6 , LiClO4, _LiBF4 , _{LiCF3SO3 , LiCF3CF2SO3} , LiC( _{CF3SO2 ) 3 ,} LiN( _CF3SO2 ) _{2 ,} LiN( _{CF3 CF2SO2 ) 2} , LiN( _{CF3SO2 )(C4F9SO2), LiN(CF3CF2CO)2 , LiBOB and the like can} be used. One type of these lithium salts may be used alone, or two or more types may be mixed.

Cyclic carbonates and chain carbonates, for example, can be used as the solvent for the electrolyte 314 . Specifically, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate and the like can be used.

The lithium ion secondary battery 301 can be manufactured, for example, by the following method. First, the electricity storage device electrodes 201 and 201' are fabricated as described in the above embodiment. Thereafter, the power storage device electrode 201 and the power storage device electrode 201 ′ are held so that the active material layers face each other with the separator 320 interposed therebetween, and are inserted into the space of the exterior body 313 . Lithium ion secondary battery 301 is completed by arranging electrolyte 314 in the space of package 313 and sealing package 313 .

According to the lithium ion secondary battery 301, the adhesion between the resin layer of the current collector and the conductive layer is enhanced. Therefore, even when the lithium ion secondary battery is used at a high temperature, the conductive layer is further suppressed from peeling off from the resin layer, and deterioration of battery characteristics due to deterioration of the current collector is suppressed.

(Example)
A current collector of an example and a current collector of a reference example were produced and their properties were evaluated.

[Preparation of sample]
Current collectors of Examples 1 to 36 and Reference Examples 1 to 4 were produced by the following method.

Examples 1 to 26
In the current collector 103 having the structure shown in FIG. 6, a current collector in which the intermediate layer 33 and the intermediate layer 33' were single layers was produced. A polyethylene terephthalate resin having a thickness of 6 μm was used for the resin layer 10 . Intermediate layers were formed on both sides of the resin layer by a sputtering method using the materials shown in Table 1 as targets. A molybdenum oxide target having an oxygen (O) content of 70 atomic % was used. The thickness of the intermediate layer was adjusted according to the deposition time and power as shown in Table 1. The thickness of the intermediate layer shown in Table 1 indicates the thickness of the intermediate layer formed on one side.

The Al conductive layers 20, 20' were formed on the intermediate layers on the respective surfaces of the resin layer 10 by vacuum deposition. The Cu conductive layers 20, 20' were formed separately into seed layers 21, 21' and main layers 22, 22'. After a seed layer 21 with a thickness of 50 nm was formed on the intermediate layer of each surface of the resin layer 10 by sputtering, the main layers 22, 22' were simultaneously formed by electroplating. The thickness of the main layers 22, 22' is adjusted by the plating time and adjusted by current density. The thickness of the conductive layer shown in Table 1 indicates the thickness of the conductive layer formed on one side.

Reference Example 1 to Reference Example 4
A current collector of Reference Example 1 was produced in the same manner as in Example 1, except that Ni was used as the intermediate layer. A current collector of Reference Example 3 was produced in the same procedure as in Example 14, except that Ni was used as the intermediate layer. The intermediate layer of Ni was formed by sputtering. A current collector of Reference Example 2 was produced in the same procedure as in Example 1, except that no intermediate layer was formed. A current collector of Reference Example 4 was produced in the same manner as in Example 14, except that no intermediate layer was formed.

Examples 27 to 36
A current collector 103 having the structure shown in FIG. 6 was produced. The first sub-intermediate layers 31, 31' and the second sub-intermediate layers 32, 32' were formed by sputtering using the materials shown in Table 2 as targets. A molybdenum oxide target having an oxygen (O) content of 70 atomic % was used. The thicknesses of the first sub-intermediate layers 31, 31' and the second sub-intermediate layers 32, 32' were adjusted by the deposition time and power. The resin layer 10 and conductive layers 20, 20' were formed in the same procedure as in Examples 1-26. In Example 36, the conductive layers 20 and 20' made of an alloy of Cu: 90 atomic %-Ni 10 atomic % were formed by vapor deposition.

[evaluation]
(1) Visual evaluation The surfaces of the current collectors produced in Examples 1 to 36 and Reference Examples 1 to 4 were observed using an optical microscope, and a unit area (300 mm horizontal × 200 mm vertical) We counted the number of wrinkles on the skin. A case with no wrinkles was evaluated as excellent (EXCELLENT), a case with 1 or 2 wrinkles was evaluated as good (GOOD), and a case with 3 or more wrinkles was evaluated as poor (POOR).

(2) Electrolyte Solution Resistance The current collectors of Examples 1 to 36 and Reference Examples 1 to 4 were held in an environment similar to that of a lithium ion secondary battery, and peeling of the conductive layer was evaluated. Specifically, a non-aqueous electrolytic solution of dimethyl carbonate containing LiPF ₆ at a concentration of 1 mol % was prepared, and water was added to the non-aqueous electrolytic solution at a rate of 1000 mass ppm.

A non-aqueous electrolyte was placed in a container, the produced current collector was immersed in the non-aqueous electrolyte in the container, the whole was sealed with a laminate film, and stored in a constant temperature bath at 85° C. for 72 hours. After that, the current collector was taken out from the laminate film and washed with an organic solvent.

Electrolyte resistance was evaluated for the obtained current collector after high-temperature storage.

Evaluation of electrolyte solution resistance was performed by two kinds of methods. The surface of the conductive layer of the current collector after high-temperature storage was rubbed with a cotton swab, and when a part of the conductive layer adhered to the cotton swab, it was determined that the conductive layer had separated from the resin layer, and it was determined to be unsatisfactory (POOR). In addition, an adhesive tape having an adhesive force of 4 N/cm was attached to the surface of the conductive layer of the current collector after high-temperature storage, and whether or not the conductive layer adhered was examined. When no peeling by the cotton swab was observed, but adhesion by the adhesive tape was observed, it was judged to be good (GOOD). When neither peeling with a cotton swab nor adhesion with an adhesive tape was observed, it was judged as excellent (EXCELLENT).

Tables 1 and 2 show the evaluation results.

[Results and Discussion]
As shown in Tables 1 and 2, the current collectors of Reference Examples 2 and 4, which do not have an intermediate layer, have poor electrolytic solution resistance regardless of whether the Al conductive layer or the Cu conductive layer is used. Moreover, as can be seen from Reference Examples 1 and 3, even when the intermediate layer of Ni is used, the resistance to the electrolytic solution is unsatisfactory.

On the other hand, when the intermediate layer contains Mo, even if the intermediate layer is composed of molybdenum metal or molybdenum oxide (Example 13), good or excellent electrolyte resistance results are obtained. It is Moreover, it can be seen that both the structure of the first embodiment and the structure of the second embodiment have conditions under which excellent resistance to the electrolyte solution can be obtained.

From these results, it is considered that when the current collector does not have an intermediate layer, the adhesion between the conductive layer and the resin layer is reduced at least after being stored in the non-aqueous electrolyte at high temperature. Further, the presence of an intermediate layer between the conductive layer and the resin layer does not necessarily mean that the adhesion is sufficiently improved, and it is considered that the main component elements contained in the intermediate layer are important. From the results in Tables 1 and 2, it is considered that when the intermediate layer contains Mo, the adhesion between the conductive layer and the resin layer is improved regardless of whether it is molybdenum oxide or metallic molybdenum. In addition, since the Cu conductive layer, the Cu—Ni conductive layer, and the Al conductive layer have the effect of improving adhesion, the present invention is applicable to both the positive electrode current collector and the negative electrode current collector. It turns out that it is possible.

From the results of Examples 1 and 14, it is considered that a favorable effect of improving adhesion can be obtained if the thickness of the intermediate layer is 2 nm or more. Further, from the results of Examples 1 to 3, 14 to 16, and 27, it is considered that the effect of improving adhesion is further enhanced when the thickness of the intermediate layer is 6 nm or more.

In the examples, a sample having an intermediate layer thickness of 1 nm was not prepared, but a film having a thickness of 1 nm can be obtained by forming a film using a general thin film forming technique such as a sputtering method or a vacuum deposition method. can be formed as a continuous film. Therefore, if the intermediate layer contains Mo and has a thickness of 1 nm or more, it is considered that the effect of improving adhesion can be obtained as discussed above.

The current collectors of Examples 9, 10, 23, and 24 were visually evaluated as good or bad. However, even with the current collectors of these samples, the resistance to the electrolyte was excellent, so even when the conductive layer was wrinkled, the adhesion between the conductive layer and the resin layer did not decrease. Conceivable. In other words, from the viewpoint of improving the adhesion between the conductive layer and the resin layer, there is no upper limit to the thickness of the intermediate layer, and even if the intermediate layer is thick, the effect of improving the adhesion can be obtained.

The wrinkles confirmed by visual evaluation are thought to be caused by damage to the resin layer due to the conditions during the formation of the intermediate layer. From the viewpoint of uniforming the thickness of the active material layer formed on the current collector as described above, the thickness of the intermediate layer is preferably less than 200 nm, and more preferably 100 nm or less. .

From these examples and reference examples, it can be seen that the current collector of the present embodiment has an intermediate layer containing Mo as a main component between the resin layer and the conductive layer. It was found that the adhesion was enhanced.

The electricity storage device electrodes according to the embodiments of the present disclosure are useful as power sources for various electronic devices, electric motors, and the like. The power storage device according to the embodiment of the present disclosure is, for example, a power source for vehicles typified by bicycles and passenger cars, a power source for communication devices typified by smartphones, a power source for various sensors, and an unmanned eXtended Vehicle ( UxV)) power supply.

10 resin layer 10a first surface 10b second surface 20, 20' conductive layers 21, 21' seed layers 22, 22' main layers 30, 33, 33' intermediate layers 30a, 33a upper surfaces 30b, 33b lower surfaces 31, 31' First sub-intermediate layer 32, 32' Second sub-intermediate layer 101, 102, 103, 210 Current collector 201, 201' Electricity storage device electrode 210s First portion 210t Second portion 220 Active material layer 301 Lithium ion secondary battery 310 Cell 311 Lead 313 Case 314 Electrolyte 320 Separator

Claims (19)

a resin layer;
a conductive layer;
an intermediate layer positioned between the resin layer and the conductive layer;
with
The conductive layer contains Al or Cu as a main component,
The intermediate layer contains Mo as a main component,
current collector. The thickness d1 of the conductive layer is
0.3 μm≦d1≦3 μm
The current collector according to claim 1, which satisfies The thickness d2 of the intermediate layer is
1 nm≦d2<200 nm
The current collector according to claim 1 or 2, which satisfies The thickness d2 of the intermediate layer is
6nm≦d2≦100nm
The current collector according to claim 1 or 2, which satisfies 5. The current collector of any one of claims 1-4, wherein the intermediate layer comprises molybdenum oxide. The intermediate layer includes a first sub-intermediate layer and a second sub-intermediate layer each containing Mo as a main component,
The first sub-intermediate layer is closer to the resin layer than the second sub-intermediate layer,
6. The current collector according to claim 5, wherein the oxygen content in the first sub-intermediate layer is higher than the oxygen content in the second sub-intermediate layer. 7. The method according to claim 5 or 6, wherein in the profile of the constituent elements of line analysis by STEM-EDX in the thickness direction of the cross section of the intermediate layer, the peak position of O is located closer to the resin layer than the peak position of Mo. Current collector as described. The thickness d3 of the first sub-intermediate layer and the thickness d4 of the second sub-intermediate layer are each 1 nm≦d3≦100 nm
1 nm ≤ d4 ≤ 100 nm
The current collector according to claim 6, which satisfies 9. The current collector according to claim 8, satisfying the relationship d3<d4. The current collector according to any one of claims 1 to 9, wherein the resin layer contains at least one selected from the group consisting of polyethylene terephthalate, polypropylene, polyamide, polyimide, polyethylene, polystyrene, phenol resin and epoxy resin. body. The current collector according to any one of claims 1 to 10;
an active material layer located on the conductive layer of the current collector;
An electrode for a power storage device. a positive electrode;
a negative electrode;
a separator disposed between the negative electrode and the positive electrode;
a non-aqueous electrolyte containing lithium ions;
with
A lithium ion secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode for a power storage device according to claim 11 . a step of preparing a resin layer;
forming an intermediate layer containing Mo as a main component on the resin layer;
and forming a conductive layer containing Al or Cu as a main component on the intermediate layer. 14. The method of manufacturing a current collector according to claim 13, wherein the intermediate layer is formed by a sputtering method using a target containing Mo. the intermediate layer comprises molybdenum oxide;
15. The method of manufacturing a current collector according to claim 14, wherein said target comprises molybdenum oxide. the intermediate layer comprises molybdenum oxide;
the target is a Mo target,
15. The method of manufacturing a current collector according to claim 14, wherein in the step of forming the intermediate layer, the intermediate layer is formed in an atmosphere containing oxygen gas. the target is a Mo target,
The intermediate layer includes a first sub-intermediate layer and a second sub-intermediate layer each containing Mo as a main component,
In the step of forming the intermediate layer,
forming the first sub-intermediate layer in an atmosphere containing oxygen gas at a first concentration;
forming the second sub-intermediate layer in an atmosphere containing oxygen gas at a second concentration lower than the first concentration;
The method for producing a current collector according to claim 14, comprising 18. The method of manufacturing a current collector according to claim 13, wherein said conductive layer contains said Al, and at least part of said conductive layer is formed by a vapor deposition method. 19. The method of manufacturing a current collector according to claim 13, wherein said conductive layer contains said Cu, and at least part of said conductive layer is formed by a plating method.

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