Electrochemical device

In an embodiment, an electrochemical device includes a winding structure which has a negative electrode, a positive electrode, and separators stacked and wound together; a negative-electrode terminal; a positive-electrode terminal; a first protective tape which covers the negative-electrode terminal and a negative-electrode active material layer; a second protective tape which covers the positive-electrode terminal and a positive-electrode active material layer; and electrolyte, wherein the positive-electrode terminal is separated from the negative-electrode terminal by a first distance. The width corresponding to the sum of a first width of the first protective tape along a winding direction of the winding structure, and a second width of the second protective tape along the winding direction, is smaller than a value obtained by multiplying the first distance by pi.

BACKGROUND

Field of the Invention

The present invention relates to an electrochemical device having current collectors, active materials, and electrode terminals.

Description of the Related Art

Representative examples of electrochemical devices include lithium ion capacitors. Some lithium ion capacitors are constituted by a cylindrical housing case that houses an electric storage element in which a negative electrode, a positive electrode, separators insulating the negative electrode and the positive electrode, an electrode terminal connected to the negative electrode, and an electrode terminal connected to the positive electrode are wound.

In such lithium ion capacitor, lithium ions are pre-doped into a negative electrode before use. The pre-doping involves, for example, providing a lithium ion supply source outside the negative-electrode terminal and positive-electrode terminal, and immersing the electric storage element in electrolyte inside the housing case. Then, as lithium ions elute into the electrolyte, those lithium ions are doped into the negative electrode of the electric storage element.

Also with lithium ion capacitors, the negative-electrode terminal is sometimes covered with a protective tape in order to prevent direct contact between the separators and the negative-electrode terminal (or positive-electrode terminal), or to suppress lithium deposition onto the negative-electrode terminal at the time of pre-doping (refer to Patent Literature 1, for example).

BACKGROUND ART LITERATURES

SUMMARY

As the electrochemical device becomes much smaller, however, the protective tape affects pre-doping more. For example, lithium ions are more likely shielded by the protective tape at the time of pre-doping, which gives rise to a possibility that lithium ions are not doped uniformly into the negative electrode after pre-doping.

In light of the aforementioned situation, an object of the present invention is to provide an electrochemical device in which lithium ions are uniformly doped into a negative electrode after pre-doping, even when the electrochemical device becomes much smaller.

Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.

To achieve the aforementioned object, an electrochemical device pertaining to an embodiment of the present invention comprises a winding structure, a negative-electrode terminal, a positive-electrode terminal, a first protective tape, a second protective tape, and electrolyte.

The winding structure has a negative electrode, a positive electrode, and separators. The negative electrode has a negative-electrode collector, and a negative-electrode active material layer provided on a principle face of the negative-electrode collector. The positive electrode has a positive-electrode collector, and a positive-electrode active material layer provided on a principle face of the positive-electrode collector. The separators insulate the negative electrode and the positive electrode. The negative electrode, the positive electrode, and the separators are stacked and wound together, with the negative electrode and the positive electrode separated by the separators.

The negative-electrode terminal is electrically connected to the negative-electrode collector. The negative-electrode terminal extends in the winding structure along a center axis of winding of the winding structure. The negative-electrode terminal projects from the winding structure.

The positive-electrode terminal is electrically connected to the positive-electrode collector. The positive-electrode terminal extends in the winding structure along the center axis of winding. The positive-electrode terminal projects from the winding structure. The positive-electrode terminal is separated from the negative-electrode terminal by a first distance. The first distance is defined as a distance or an average distance, if applicable, in a straight line between a center of the positive-electrode terminal and the a center of the negative-electrode terminal on a plane passing through the winding structure in a direction orthogonal to the center axis of winding of the winding structure.

The first protective tape covers the negative-electrode terminal and the negative-electrode active material layer.

The second protective tape covers the positive-electrode terminal and the positive-electrode active material layer.

The electrolyte immerses the positive electrode, the negative electrode, and the separators.

The width corresponding to the sum of a first width of the first protective tape along a winding direction of the winding structure, and a second width of the second protective tape along the winding direction, is smaller than a value obtained by multiplying the first distance by pi (π). Each of the first and second widths is defined as a width or an average width, if applicable, measured along the winding direction/surface on a plane passing through the winding structure and the corresponding protective tape in a direction orthogonal to the center axis of winding of the winding structure.

According to the electrochemical device described above, lithium ions are less likely shielded by the first protective tape or second protective tape at the time of pre-doping. As a result, lithium ions are more uniformly doped into the negative electrode.

With the aforementioned electrochemical device, lithium ions may be pre-doped into the negative-electrode active material layer.

This way, lithium ions are more uniformly doped into the negative electrode through pre-doping.

With the aforementioned electrochemical device, the first protective tape may not overlap the second protective tape in the direction from the center axis of winding toward an outer periphery of the winding structure.

This way, lithium ions pass between the first protective tape and the second protective tape during pre-doping, and are thus doped into the negative electrode more uniformly.

With the aforementioned electrochemical device, the first distance may be 8 mm or less.

This means that lithium ions are less likely shielded by the first protective tape or the second protective tape during pre-doping, even when the first distance of the electrochemical device is 8 mm or less, and are thus doped into the negative electrode more uniformly.

With the aforementioned electrochemical device, an outer diameter of the winding structure may be 30 mm or less.

This means that lithium ions are less likely shielded by the first protective tape or the second protective tape during pre-doping, even when the outer diameter of the winding structure of the electrochemical device is 30 mm or less, and are thus doped into the negative electrode more uniformly.

With the aforementioned electrochemical device, the first width equals X % of the aforementioned value (X≥12.0), while the second width is smaller than (100−X)%.

According to the protective tapes meeting these ranges of values, lithium ions are less likely shielded by the first protective tape or the second protective tape during pre-doping, and are thus doped into the negative electrode more uniformly.

As described above, according to the present invention, lithium ions are more uniformly doped into the negative electrode after pre-doping, even when the electrochemical device becomes smaller.

DESCRIPTION OF THE SYMBOLS

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention is explained below by referring to the drawings. XYZ-axis coordinates may be applied in each drawing.

An overview of an electrochemical device100pertaining to this embodiment is explained below. The electrochemical device illustrated in this embodiment is a lithium ion capacitor. Details of an electric storage element110A contained in the electrochemical device100are described later.

FIG. 1is a schematic oblique view showing the appearance of the electrochemical device100pertaining to this embodiment.

With the electrochemical device100shown inFIG. 1, the electric storage element110A is housed in a housing case120. In addition to the electric storage element110A, the housing case120is also filled with electrolyte. With the electrochemical device100, the electric storage element110A is immersed in the electrolyte. A lid (not illustrated) is provided on the electric storage element110A, and the electrolyte is sealed by the housing case120and the lid.

The electrochemical device100in which the electric storage element110A is immersed in the electrolyte has completed pre-doping. For example, the electric storage element110A has a lithium ion supply source before it is immersed in the electrolyte (described later). Then, when the electric storage element110A is immersed in the electrolyte, lithium ions elute from the lithium ion supply source into the electrolyte, and those lithium ions are doped into the negative electrode of the electric storage element110A.

[Constitution of Electric Storage Element]

FIG. 2Ais a schematic oblique view showing the electric storage element110A pertaining to this embodiment.FIG. 2Bis a schematic side view showing a negative electrode130, a negative-electrode terminal131, and a protective tape161pertaining to this embodiment.FIG. 2Cis a schematic side view showing a positive electrode140, a positive-electrode terminal141, and a protective tape171pertaining to this embodiment.

FIGS. 2A, 2B, and 2Cshow the electric storage element110A in a state before pre-doping, where the electric storage element110A is not yet immersed in the electrolyte.

As shown inFIG. 2A, the electric storage element110A has the negative electrode130, the positive electrode140, the negative-electrode terminal131, the positive-electrode terminal141, a winding core112, separators150, and a lithium electrode180. The electric storage element110A illustrated inFIG. 2Ais an electric storage element before pre-doping. The negative electrode130is an electrode capable of occluding lithium ions. The positive electrode140is a polarizable electrode. With such electric storage element, preferably lithium ions are more uniformly doped into the negative electrode after pre-doping.

In this embodiment, the direction in which the winding core112extends represents a Z-axis direction. An X-axis direction represents a direction orthogonal to the Z-axis direction. A Y-axis direction represents a direction orthogonal to the X-axis direction and Z-axis direction. The direction in which the winding core112extends (the direction parallel with a center axis of winding C1) is also the direction in which the negative-electrode terminal131and the positive-electrode terminal141extend. Also, with the electric storage element110A, the direction from the center axis of winding C1toward an outer periphery of the electric storage element110A represents an outer direction, and the opposite direction of the outer direction represents an inner direction. This embodiment also includes in its scope those structures where no winding core112is provided in the electric storage element110A.

The negative electrode130, the positive electrode140, and the separators150are stacked from the winding core112toward the outer side. The separators150separate the positive electrode140and the negative electrode130. The separators150insulate the negative electrode130and the positive electrode140. The negative electrode130and the positive electrode140are both wound around the winding core112. The separators150are placed between the negative electrode130and the positive electrode140and wound around the winding core112. In this embodiment, the structure that includes the negative electrode130, the positive electrode140, and the separators150is referred to as a winding structure111. An outer diameter R of the winding structure111is 30 mm or less, for example. The outer diameter R of the winding structure111may be greater than 30 mm.

For example,FIG. 2Bshows the negative electrode130, the negative-electrode terminal131, and the protective tape161in a stage before the winding structure111is wound. The negative electrode130has a negative-electrode collector132and a negative-electrode active material layer133. The negative-electrode terminal131is electrically connected to the negative-electrode collector132of the negative electrode130. The negative-electrode terminal131is joined to the negative-electrode collector132on which the negative-electrode active material layer133is not provided, by means of needle-clinching using pin members131p, for example. The negative-electrode terminal131extends in the winding structure111along the center axis of winding C1of the winding structure111. The negative-electrode terminal131projects from the winding structure111.

The protective tape161(a first protective tape) covers the negative-electrode terminal131. The protective tape161covers the negative-electrode terminal131and the negative-electrode active material layer133. The protective tape161has a width161w(a first width) along a winding direction Dr. The winding direction Dr is the direction in which the negative electrode130, the positive electrode140, and the separators150are wound around the center axis of winding C1.

Also,FIG. 2Cshows the positive electrode140, the positive-electrode terminal141, and the protective tape171in a stage before the winding structure111is wound. The positive electrode140has a positive-electrode collector142and a positive-electrode active material layer143. The positive-electrode terminal141is electrically connected to the positive-electrode collector142of the positive electrode140. The positive-electrode terminal141is joined to the positive-electrode collector142on which the positive-electrode active material layer143is not provided, by means of needle-clinching using pin members141p, for example. The positive-electrode terminal141extends in the winding structure111along the center axis of winding C1. The positive-electrode terminal141projects from the winding structure111. For example, the positive-electrode terminal141projects from the winding structure111in the same direction as the negative-electrode terminal131.

The protective tape171(a second protective tape) covers the positive-electrode terminal141. The protective tape171covers the positive-electrode terminal141and the positive-electrode active material layer143. The protective tape171has a width171w(a second width) along the winding direction Dr.

The negative-electrode terminal131and the positive-electrode terminal141each contain at least one of copper, aluminum, iron, etc. for example. The negative-electrode terminal131is a copper terminal, for example. The positive-electrode terminal141is an aluminum terminal, for example.

As shown inFIG. 2A, the positive-electrode terminal141is separated from the negative-electrode terminal131by a distance D (a first distance). The distance D is defined by the distance between the center of the positive-electrode terminal141and the center of the negative-electrode terminal131in the X-Y plane. The distance D is 8 mm or less, for example. The distance D may be greater than 8 mm.

With the electric storage element110A, the width corresponding to the sum of the width161wof the protective tape161and the width171wof the protective tape171is smaller than a value obtained by multiplying the distance D by pi π ((Width161w+Width171w)<D×π - - - (1)). D×π is equivalent to the circumference of a circle of which the diameter is D. The widths161wand171ware each variable. However, the widths161wand171wsatisfy the relationship of Expression (1) above. Also, the width161wmay be different from the width171w. For example, the width161wequals X % of the value of (D×π) (X≥12.0), while the width171wis smaller than (100−X)%. Furthermore, the protective tape161does not overlap the protective tape171in the direction from the center axis of winding C1toward the outer periphery of the winding structure111.

Also, in the example ofFIG. 2A, the center of the protective tape171, the winding core112(the center axis of winding C1), and the center of the protective tape161are arranged in this order along a single line. Furthermore, in the example ofFIG. 2A, the width161wis the same as the width171w. It should be noted that the center of the protective tape171, the winding core112(the center axis of winding C1), and the center of the protective tape161need not be arranged along a single line. For example, the angle formed by the line drawn from the center axis of winding C1to the center of the protective tape171, and the line drawn from the center axis of winding C1to the center of the protective tape161, may be smaller than 180 degrees.

The lithium electrode180is electrically connected to the negative electrode130. The lithium electrode180is placed on the outer side of the negative-electrode terminal131and the positive-electrode terminal141. In the example ofFIG. 2A, the winding structure111is surrounded by the lithium electrode180. This lithium electrode180has a metal foil and a lithium layer, for example. The position at which the lithium electrode180is placed is not limited to the one in the example ofFIG. 2A. Also, the positions at which the separators150are placed are not limited to the ones in the example ofFIG. 2. For example, while the lithium electrode180is exposed from the separators150in the example ofFIG. 2A, the lithium electrode180may be surrounded by the separators150.

A cross-sectional structure of the electric storage element110A, obtained by cutting it along the X-Y plane, is explained in greater detail.

FIG. 3is a schematic cross-sectional view, along the X-Y plane, of the electric storage element110A pertaining to this embodiment.

FIG. 3shows how the cross-section of the electric storage element110A, obtained by cutting it along the X-Y plane, looks when the electric storage element110A is viewed from below.

FIG. 4Ais a schematic cross-sectional view ofFIG. 3along the A1-A2line.FIG. 4Bis a schematic cross-sectional view showing an enlarged view around the negative-electrode terminal131illustrated inFIG. 3.FIG. 4Cis a schematic cross-sectional view showing an enlarged view around the positive-electrode terminal141illustrated inFIG. 3.

With the negative electrode130, the negative-electrode active material layer133is provided on principle faces132aand132bof the negative-electrode collector132. A part of the negative-electrode active material layer133is detached from the principle face132aof the negative-electrode collector132. The negative-electrode terminal131is connected to this detached part of the negative-electrode collector132.

The negative-electrode terminal131and the negative-electrode active material layer133around the negative-electrode terminal131are covered by the protective tape161. This way, the negative-electrode collector132is sealed by the protective tape161where the negative-electrode collector132is exposed because the negative-electrode active material layer133is detached.

The protective tape161faces the winding core112across the negative electrode130, the positive electrode140, and the separators150. If the negative-electrode terminal131is not covered by the protective tape161during pre-doping, lithium may preferentially deposit onto the negative-electrode terminal131. For this reason, preferably the negative-electrode terminal131is covered by the protective tape161so that the negative-electrode terminal131is shielded from the electrolyte.

With the positive electrode140, the positive-electrode active material layer143is provided on principle faces142a,142bof the positive-electrode collector142. The positive-electrode terminal141is electrically connected to the positive-electrode collector142. For example, a part of the positive-electrode active material layer143is detached from the principle face142aof the positive-electrode collector142. The positive-electrode terminal141is connected to this detached part of the positive-electrode collector142.

The positive-electrode terminal141and the positive-electrode active material layer143around the positive-electrode terminal141are covered by the protective tape171. The protective tape171faces the winding core112across the negative electrode130, the positive electrode140, and the separators150.

A width131wof the negative-electrode terminal131is 2 mm or more, so as to ensure stable machining or adequate mechanical strength for the negative-electrode terminal131. Similarly, a width141wof the positive-electrode terminal141is 2 mm or more, so as to ensure stable machining or adequate mechanical strength for the positive-electrode terminal141. Also, the width161wof the protective tape161covering the negative-electrode terminal131is 3 mm or more. The width171wof the protective tape171covering the positive-electrode terminal141is 3 mm or more. However, the sum of the widths161wand171wsatisfies Expression (1) above.

The separators150include a separator150aand a separator150b. The separators150aand150binsulate the negative electrode130and the positive electrode140. The separators150aand150bseparate the negative electrode130and the positive electrode140, while letting the ions contained in the electrolyte pass through the separators150aand150b. Also, the separators150aand150bmay constitute one continuous separator.

With the electric storage element110A in which the negative electrode130, the positive electrode140, and the separators150are wound, the principle face132aof the negative-electrode collector132and the principle face142aof the positive-electrode collector142constitute the inner faces of winding. Also, the principle face132bof the negative-electrode collector132and the principle face142bof the positive-electrode collector142constitute the outer faces of winding. In the examples ofFIGS. 3, 4B and 4C, the protective tapes161and171are placed on the inner side of winding.

The lithium electrode180is placed on the outer side of the negative-electrode terminal131and the positive-electrode terminal141. With the winding structure111illustrated inFIG. 3, the electrode on the outermost side of winding (an outermost periphery) is the negative electrode130, and the lithium electrode180is connected to the negative-electrode collector132on this outermost side of winding. The lithium electrode180is placed in a manner surrounding the winding structure111, for example. The lithium electrode180has a metal foil181and a lithium layer183. The metal foil181is a copper foil, for example. The lithium layer183is a lithium foil, for example. The quantity of the lithium layer183is adjusted to a level at which lithium ions can be doped into the negative-electrode active material layer133at the time of lithium ion pre-doping. The lithium layer183may be provided over the entire surface of the metal foil181, or it may be provided selectively on the metal foil181.

The metal foil181is electrically connected to the negative-electrode collector132. For example, the metal foil181is joined to the negative-electrode collector132by means of needle-clinching, welding, etc. The metal foil181is placed on the outer side of the winding structure111in a manner wrapping around the winding structure111once. With the metal foil181, a principle face181aconstitutes the inner face of winding, while a principle face181bconstitutes the outer face of winding. The width of the metal foil181in the Z-axis direction is the same as the width of the negative-electrode collector132in the Z-axis direction, for example.

The lithium layer183functions as a lithium ion supply source when lithium ions are pre-doped into the negative-electrode active material layer133. For this reason, preferably the lithium layer183is provided on the principle face181aon the inner side of winding, instead of the principle face181bon the outer side of winding. This way, during pre-doping, lithium ions diffuse from the principle face181aof the metal foil181into the winding structure111, through the electrolyte, without being shielded by the metal foil181. It should be noted that, if the lithium layer183is provided on the principle face181b, multiple through holes may be formed in the metal foil181to let lithium ions pass through the metal foil181.

The separator150ais placed between the lithium electrode180and the positive electrode140. This way, the lithium electrode180is insulated from the positive electrode140.

Also, in this embodiment, the lithium electrode180need not be placed in a manner surrounding the winding structure111. For example, the lithium electrode180may be placed inside the winding structure111, so long as the lithium electrode180is on the outer side of the negative-electrode terminal131and the positive-electrode terminal141. In this case, the lithium electrode180is also connected to the negative electrode130electrically. When the electric storage element110A described above is immersed in the electrolyte, lithium ions are pre-doped into the negative-electrode active material layer133.

Specific examples of the material of the electric storage element110A are explained.

The negative-electrode collector132may be a metal foil, for example. Multiple through holes may be provided on the metal foil. The negative-electrode collector132may be a copper foil, etc., for example. The negative electrode active material contained in the negative-electrode active material layer133is capable of occluding the lithium ions in the electrolyte, and may be non-graphitizing carbon (hard carbon), graphite, soft carbon, or other carbon material, for example. The negative-electrode active material layer133may be a mixture of the negative electrode active material and binder resin, and may further contain conductive agent. For example, the negative-electrode active material layer133is produced by coating a slurry mixture of any of the active materials mentioned above, conductive agent, and synthetic resin onto a base, forming it into a sheet, and then cutting the sheet.

The binder resin may be any synthetic resin that joins the negative electrode active material. The binder resin may be carboxymethyl cellulose, styrene butadiene rubber, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, fluororubber, polyvinylidene fluoride, isoprene rubber, butadiene rubber, ethylene propylene rubber, or the like, for example.

The conductive agent is constituted by grains made of conductive material, and any conductive agent may be used so long as it improves the conductivity within the negative electrode active material. Examples of the conductive agent include acetylene black, graphite, highly conductive carbon black, other carbon materials, and the like. Any one of the foregoing may be used alone, or two or more of them may be mixed together. It should be noted that the conductive agent may also be a metal material, conductive polymer, or other material so long as it exhibits conductivity.

The material of the positive-electrode collector142may be the same as, or different from, the material of the negative-electrode collector132. As the positive electrode active material, the positive-electrode active material layer143contains at least one of active materials such as active carbon and PAS (Polyacenic Semiconductor). The positive-electrode active material layer143is produced by coating a slurry mixture of any of the active materials mentioned above, a conductive agent (such as highly conductive carbon black), and synthetic resin (such as PTFE) onto a base, forming it into a sheet, and then cutting the sheet. The material of the positive-electrode active material layer143may be the same as the material of the negative-electrode active material layer133.

The separators150(the separators150aand150b) may each be a sheet material that lets electrolytic ions pass through the material but insulates the negative electrode130and the positive electrode140. The separators150may be woven fabric, nonwoven fabric, microporous films of synthetic resin, etc. The separators150may be porous sheets made of glass fibers, cellulose fibers, plastic fibers, etc.

For the electrolyte, any desired composition can be selected. As cations, for example, the electrolyte may contain at least lithium ions, but tetraethyl ammonium ions, triethyl methyl ammonium ions, 5-azoniaspiro [4.4] nonane ions, ethyl methyl imidazolium ions, etc., may also be mixed in. As anions, the electrolyte may contain BF4−(tetrafluoroborate ions), PF6−(hexafluorophosphate ions), (CF3SO2)2N−(TFSA ions), etc. As solvent, the electrolyte may contain propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, sulfolane, dimethyl sulfone, ethyl methyl sulfone, ethyl isopropyl sulfone, etc. To be specific, the electrolyte may be a propylene carbonate solution of lithium tetrafluoroborate (LiBF4), lithium hexafluorophosphate (LiPF6), or the like.

For the protective tapes161and171, materials that are heat-resistant and also resistant to the electrolyte are applied. For example, the protective tapes161and171may contain any one of polyimide, polypropylene, polyphenylene sulfide, and the like.

[Operations of Electric Storage Element]

Before the operations of the electric storage element110A pertaining to this embodiment are explained, the operations of the electric storage elements pertaining to comparative examples are explained. When the electric storage element becomes much smaller, the widths of the protective tapes must be decreased according to the degree of this size reduction; otherwise, the protective tapes become relatively wider in the electric storage element. An example of this is shown inFIGS. 5A and 5B.

FIGS. 5A and 5Bare schematic cross-sectional views showing the operations of an electric storage element210A pertaining to a comparative example.

InFIGS. 5A and 5B, some parts of the electric storage element210A are omitted to illustrate a simplified version of the electric storage element210A, in order to clarify the positional relationships of protective tapes261and271and a lithium layer283.FIG. 5Ashows the electric storage element210A in a state before lithium ions are pre-doped into an negative electrode, whileFIG. 5Bshows the electric storage element210A in a state after the electric storage element210A is immersed in the electrolyte inside a housing case220, and lithium ions are doped into the negative electrode.

With the electric storage element210A shown inFIG. 5A, the width corresponding to the sum of a width261wof the protective tape261and a width271wof the protective tape271is equal to or greater than the circumference of a circle215with a diameter D ((Width261w+Width271w)≥D×π). Such structure could be formed when the electric storage element becomes much smaller, but the widths of the protective tapes261and271are not adjusted according to this scale of size reduction. For example, the electric storage element becomes much smaller when the distance D is 8 mm or less, or the outer diameter of a winding structure211is 30 mm or less. In this case, the widths of the protective tapes261and271must be decreased according to the outer diameter R; otherwise, a constitution where the protective tapes261and271surround the circle215results, as is the case of the electric storage element210A. It should be noted that, in the example ofFIGS. 5A and 5B, the symbol “281” corresponds to a metal foil, the symbol “231” corresponds to a negative-electrode terminal, and the symbol “241” corresponds to a positive-electrode terminal.

As the electric storage element210A is immersed in the electrolyte, lithium ions elute from the lithium layer283into the electrolyte, and those lithium ions are doped into the negative electrode of the electric storage element210A. For example, the lithium ions diffuse from the lithium layer283toward the center axis of winding C1.

However, the protective tapes261and271exist between an outer periphery of the winding structure211and the center axis of winding C1. Furthermore, the width corresponding to the sum of the width261wof the protective tape261and the width271wof the protective tape271is equal to or greater than the circumference of the circle215. In other words, the winding structure211is configured such that the area inside the circle215is demarcated by the protective tapes261and271.

The result of this is that with the electric storage element210A, lithium ions are shielded by the protective tapes261and271at the time of lithium ion pre-doping, and consequently lithium ions do not spread fully inside the circle215. For example,FIG. 5Bprovides a schematic representation of the lithium ions that have been doped into the winding structure211, as dots.FIG. 5Bshows that the lithium ion concentration is relatively higher on the outer side of the protective tapes261and271.

Also,FIGS. 6A and 6Bare schematic cross-sectional views showing the operations of an electric storage element210B pertaining to another comparative example.

FIG. 6Ashows a state before lithium ions are pre-doped into a negative electrode, whileFIG. 6Bshows a state after lithium ions are pre-doped into the negative electrode.

With the electric storage element210B shown inFIG. 6A, the width corresponding to the sum of the width261wof the protective tape261and the width271wof the protective tape271is smaller than the circumference of the circle215with the diameter D. With the electric storage element210B, however, a part of the protective tape261is overlapping a part of the protective tape271. Such constitution could also be formed when the electric storage element210B becomes much smaller, but the widths of the protective tapes261and271are not adjusted according to this scale of size reduction.

With the electric storage element210B, lithium ions enter the circle215from the non-overlapping parts of the protective tapes261and271at the time of pre-doping, for example (FIG. 6B). However, the lithium ions are shielded by the overlapping parts of the protective tapes261and271, and consequently do not spread uniformly into the circle215. For example, an area with high lithium ion concentration283H may be formed locally on the outer side of the protective tapes261and271. Or, an area with low lithium ion concentration283L may be formed locally on the inner side of the protective tapes261and271.

As described above, lithium ions may not be uniformly doped into the negative electrode, in the case of the electric storage elements210A and210B pertaining to the comparative examples.

On the other hand,FIGS. 7A and 7Bare schematic cross-sectional views showing the operations of the electric storage element110A pertaining to this embodiment.

FIG. 7Ashows a state before lithium ions are pre-doped into the negative electrode130, whileFIG. 7Bshows a state after lithium ions are pre-doped into the negative electrode130.

With the electric storage element110A, the width corresponding to the sum of the width161wof the protective tape161and the width171wof the protective tape171is smaller than the circumference of a circle115with diameter D ((Width161w+Width171w)<D×π). Furthermore, the protective tape161does not overlap the protective tape171in the direction from the center axis of winding C1toward the outer periphery of the winding structure111.

Such structure makes lithium ions less likely to be shielded by the protective tapes161and171at the time of lithium ion pre-doping. For example, the electric storage element110A has two gaps between the protective tapes161and171, while the electric storage element210B has one such gap. Furthermore, when the protective tape161, the center axis of winding C1, and the protective tape171are lined up, these two gaps are positioned in a point-symmetric manner with respect to the center axis of winding C1. This way, lithium ions can more uniformly diffuse inside and outside the circle115(FIG. 7B). The result is that, with the electric storage element110A, lithium ions are more uniformly doped into the negative electrode130.

As described above, the electric storage element110A is structured in such a way that Expression (1) above is satisfied, and the protective tapes161and171do not overlap each other, even when the distance D is 8 mm or less, or the outer diameter of the winding structure111is 30 mm or less. With such structure, lithium ions are more uniformly doped into the negative electrode130.

[Variation Example of Electrochemical Device]

FIG. 8is a schematic cross-sectional view showing an electric storage element110B pertaining to a variation example of this embodiment.

The electric storage element110B shown inFIG. 8further has a protective tape162and a protective tape172.

The negative-electrode terminal131is covered by the protective tape162from the opposite side of the center axis of winding C1.

The protective tape162faces the protective tape161across the negative-electrode terminal131and the negative-electrode collector132. The protective tape161is positioned between the protective tape162and the center axis of winding C1. The protective tape162has a width162win the winding direction Dr. Furthermore, the protective tape162does not overlap the protective tape172in the direction from the center axis of winding C1toward the outer periphery of the winding structure111. Also, the protective tape172, the winding core112(the center axis of winding C1), and the protective tape162are arranged in this order along a single line.

For example, the negative-electrode terminal131may be joined to the negative-electrode collector132by means of needle-clinching, and a needle member may pierce through the reverse side of the negative-electrode collector132and also through the negative-electrode active material layer133provided on the reverse side of the negative-electrode collector132. Should this happen, the projecting part of the needle member is covered with the protective tape162, so that lithium deposition onto the projecting needle member can be suppressed. Also, the protective tape162prevents the projecting needle member from contacting the adjacent separator. Or, if the needle member breaks through the separator, the protective tape162prevents the needle member from directly contacting the positive-electrode active material layer143.

Also, the positive-electrode terminal141is covered by the protective tape172from the opposite side of the center axis of winding C1. The protective tape172faces the protective tape171across the positive-electrode terminal141and the positive-electrode collector142. The protective tape171is positioned between the protective tape172and the center axis of winding C1. The protective tape172has a width172win the winding direction Dr. In the example ofFIG. 8, the width162wis the same as the width172w. It should be noted that the protective tape172, the winding core112(the center axis of winding C1), and the protective tape162need not be arranged along a single line. Furthermore, the width162wmay be different from the width172w.

For example, the positive-electrode terminal141may be joined to the positive-electrode collector142by means of needle clinching, and a needle member may pierce through the reverse side of the positive-electrode collector142and also through the positive-electrode active material layer143provided on the reverse side of the positive-electrode collector142. Should this happen, the projecting part of the needle member is covered with the protective tape172, so that direct contact of the projecting needle member with the adjacent negative-electrode active material layer133can be avoided.

Furthermore, the width corresponding to the sum of the width162wof the protective tape162and the width172wof the protective tape172is smaller than the value obtained by multiplying the distance D by pi π ((Width162w+Width172w)<D×π - - - (2)). The widths162wand172ware each variable. However, the widths162wand172wsatisfy the relationship of Expression (2) above. The width162wequals X % of the value of (D×π) (X≥12.0). The width172wis smaller than (100−X)%.

According to such structure, or specifically the structure whereby Expression (2) above is satisfied, and the protective tapes162and172do not overlap each other, even when the distance D is 8 mm or less, or the outer diameter of the winding structure111is 30 mm or less, lithium ions are more uniformly doped into the negative electrode130.

The foregoing explains an embodiment of the present invention; needless to say, however, the present invention is not limited to the aforementioned embodiment, and various changes may be added.

In the present disclosure where conditions and/or structures are not specified, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, in the present disclosure including the examples described above, any ranges applied in some embodiments may include or exclude the lower and/or upper endpoints, and any values of variables indicated may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, “a” may refer to a species or a genus including multiple species, and “the invention” or “the present invention” may refer to at least one of the embodiments or aspects explicitly, necessarily, or inherently disclosed herein. The terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

The present application claims priority to Japanese Patent Application No. 2016-204447, filed Oct. 18, 2016, the disclosure of which is incorporated herein by reference in its entirety including any and all particular combinations of the features disclosed therein.