Electrode plate for power storage devices and power storage device

An electrode plate for power storage devices having a high capacity and a power storage device including the electrode plate for power storage devices, an exemplary embodiment includes a strip-shaped positive electrode core and a positive electrode active material layer provided on at least one surface of the positive electrode core. A bare part is formed in an end portion of the positive electrode core in the width direction. The bare part is a part in which the surface of the core is exposed and to which a positive electrode lead is to be connected. The positive electrode active material layer has a thin part in at least part of a first region aligned with the bare part in the longitudinal direction of the positive electrode core. The thin part is thinner than a second region, which is a region other than the first region.

TECHNICAL FIELD

The present disclosure relates to an electrode plate for power storage devices and a power storage device.

BACKGROUND ART

There is a need to improve electrode plates in order to increase the energy density of power storage devices. For example, Patent Literature 1 and Patent Literature 2 each disclose an electrode plate including a bare part formed in part of a core in the width direction (an end portion in the width direction) in order to increase the capacity of a non-aqueous electrolyte secondary battery. The bare part is a part in which the surface of the core is exposed and to which an electrode plate lead is to be connected. Since the active material layer of such an electrode plate has a larger area than the active material layer of an electrode plate having a bare part formed over the full width of a core, such an electrode plate increases the capacity of a battery. The width direction of the electrode plate corresponds to the axial direction of a wound-type electrode body, and the longitudinal direction corresponds to the winding direction of the electrode body.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

When a bare part is formed in an end portion of a core in the width direction, a lead will be unevenly connected to the end portion in the width direction of the core. A lead is typically thicker than an active material layer. In a wound-type electrode body including the electrode plate disclosed in Patent Literature 1 or 2, an end portion of the electrode body in the axial direction thus protrudes locally due to the influence of the thickness of the lead connected to the end portion of the core in the width direction. Because of this configuration, the use of such an electrode plate makes it difficult to stably form a winding structure on the winding outer side with respect to a lead connection part and tends to cause winding misalignment in the electrode body.

Solution to Problem

An electrode plate for power storage devices in an aspect of the present disclosure is an electrode plate for power storage devices that is used to form a wound-type electrode body. The electrode plate for power storage devices includes a strip-shaped core, and an active material layer provided on at least one surface of the core. A bare part is formed in an end portion of the core in the width direction and at a position distant from a first end portion of the core in the longitudinal direction. The bare part is a part in which the surface of the core is exposed and to which a lead is to be connected. The first end portion is located on the winding outer side of the electrode body. The active material layer includes a thin part in at least part of a first region aligned with the bare part in the longitudinal direction of the core. The thin part is thinner than a second region, which is a region other than the first region.

A power storage device in an aspect of the present disclosure includes the electrode plate for power storage devices as at least one of a positive electrode plate and a negative electrode plate.

Advantageous Effects of Invention

According to the electrode plate for power storage devices of the present disclosure, the winding misalignment of the electrode body can be minimized sufficiently even when a lead is connected to a bare part formed in an end portion of a core in the width direction.

DESCRIPTION OF EMBODIMENTS

In an electrode plate for power storage devices of the present disclosure, a bare part in which the surface of the core is exposed and which serves as a part to which a lead is to be connected is formed in part of a core in the width direction (an end portion in the width direction) in order to increase the area of an active material layer as large as possible and thus to increase the energy density of a power storage device. When a lead is connected to the full width of the core, winding misalignment is unlikely to occur because a wound-type electrode boy protrudes over the substantially full length in the axial direction α (seeFIG. 2). However, when a lead is connected to an end portion of the core in the width direction, an end portion of the electrode body in the axial direction locally protrudes, and winding misalignment tends to occur on the winding outer side with respect to the lead. Specifically, the electrode plate that forms a winding structure shifts in the axial direction α, and the end portion of the electrode body in the axial direction waves, and it is thus difficult to adjust the entire end portion at the same level in the axial direction.

The inventors of the present invention have diligently carried out studies to solve the aforementioned problems and, as a result, found out a new electrode-plate structure in which the first region, which is a region of the active material layer aligned with the bare part in the longitudinal direction of the core that corresponds to the winding direction γ (seeFIG. 2) of the electrode body, has a thin part having a small thickness. According to the electrode plate of the present disclosure, the thin part formed in the first region absorbs a difference in thickness between the lead and the active material layer (second region) and minimizes winding misalignment of the electrode body. Since the first region of the active material layer overlaps the bare part in the radial direction β (seeFIG. 2) in a wound-type electrode body, that is, in the stacking direction of the electrode body, the bare part being a part to which a lead is connected, the influence of the thickness of the lead can be reduced by making the first region thinner than the second region.

The effect of minimizing winding misalignment is also obtained even when the thin part is formed in a narrow area. Preferably, the thin part is formed on the winding outer side with respect to the bare part or in substantially all parts of the first region.

Hereinafter, exemplary embodiments will be described in detail.

The drawings to which reference is made in the description of the embodiments are schematically illustrated. The dimensional ratios and the like of components in the drawings may be different from actual dimensional ratios and the like. Specific dimensional ratios and the like should be determined in light of the following description. As used therein, the term “substantially” is intended to describe substantially the same feature as an example and include completely the same feature and substantially the same feature. The term “end portion” refers to an end of an object and surroundings of the end. The term “central portion” refers to the center of an object and surroundings of the center.

In exemplary embodiments, a cylindrical battery having a cylindrical metal case (non-aqueous electrolyte secondary battery10) and a battery electrode plate (positive electrode plate11) included in the battery are illustrated. A power storage device and an electrode plate for power storage devices according to the present disclosure are not limited to these. The power storage device of the present disclosure may be, for example, a prismatic battery having a prismatic metal case or may be a laminate-type battery having an outer body formed of a resin sheet. Alternatively, the power storage device according to the present disclosure may be a capacitor, and the electrode plate for power storage devices according to the present disclosure may be used as a capacitor electrode plate.

Referring toFIG. 1toFIG. 9, the non-aqueous electrolyte secondary battery10according to an exemplary embodiment and electrode plates included in the battery will be described below in detail.FIG. 1is a sectional view of the non-aqueous electrolyte secondary battery10.FIG. 2is a perspective view of an electrode body14included in the non-aqueous electrolyte secondary battery10.

As illustrated inFIG. 1andFIG. 2, the non-aqueous electrolyte secondary battery10includes a positive electrode plate11, a negative electrode plate12, and a non-aqueous electrolyte (not shown). The positive electrode plate11and the negative electrode plate12together with a separator13form the electrode body14. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte containing a gel polymer or the like. In the example illustrated inFIG. 1, a case body15having a bottomed cylindrical shape and a sealing body16form a metal battery case for accommodating the electrode body14and the non-aqueous electrolyte.

The non-aqueous electrolyte secondary battery10preferably includes insulating plates17and18, which are disposed above and below the electrode body14, respectively. In the example illustrated inFIG. 1, a positive electrode lead19attached to the positive electrode plate11passes through a through-hole of the insulating plate17and extends toward the sealing body16, whereas a negative electrode lead20attached to the negative electrode plate12passes outside the insulating plate18and extends toward the bottom of the case body15. The positive electrode lead19is welded to the lower surface of a filter22, which is a bottom plate of the sealing body16. A cap26is a top plate of the sealing body16and is electrically connected to the filter22. The cap26serves as a positive electrode terminal. The negative electrode lead20is welded to the bottom inner surface of the case body15. The case body15serves as a negative electrode terminal.

The electrode body14is a wound-type electrode body formed by spirally winding the positive electrode plate11and the negative electrode plate12with the separator13interposed therebetween. The positive electrode plate11, the negative electrode plate12, and the separator13each have a strip shape and are spirally wound so that the positive electrode plate11, the negative electrode plate12, and the separator13are alternately stacked on top of one another in the radial direction β of the electrode body14. In the electrode body14, the longitudinal direction of each electrode plate corresponds to the winding direction γ, and the width direction of each electrode plate corresponds to the axial direction α. The separator13is formed of an insulating porous sheet (microporous membrane) having ion permeability. Suitable examples of the separator13include a polyethylene microporous membrane. The thickness of the separator13is, for example, 10 μm to 50 μm. The positive electrode plate11and the negative electrode plate12will be described below in detail.

The electrode body14includes a positive electrode lead19and a negative electrode lead20in addition to the positive electrode plate11, the negative electrode plate12, and the separator13. Each lead is attached to the core of the corresponding electrode (see, for example,FIG. 5described below). In the example illustrated inFIG. 2, the positive electrode lead19is attached to a central portion in the longitudinal direction distant, from a winding outer side-end portion11aof the positive electrode plate11. The positive electrode lead19is sandwiched between a stack of the positive electrode plate11, the negative electrode plate12, and the separator13and a stack of the positive electrode plate11, the negative electrode plate12, and the separator13from both sides in the radial direction β of the electrode body14. The negative electrode lead20is attached to a winding outer-side end portion12aof the negative electrode plate12. The positive electrode lead19extends from a first end portion of the electrode body14in the axial direction α. The negative electrode lead20extends from a second end portion of the electrode body14in the axial direction α. The thickness of the positive electrode lead19is preferably 150 μm to 500 μm in view of, for example, the current collecting performance of the positive electrode plate11, the durability (prevention from fracture) of the lead, and downsizing of the electrode body14. In general, the positive electrode lead19is thicker than the positive electrode active material layer (seeFIG. 6described below).

One lead is attached to each electrode in this embodiment, but a plurality of leads may be attached to each electrode. The positions at which the leads are attached to the corresponding electrodes are not limited to the positions illustrated inFIG. 2. For example, the positive electrode lead19may be attached to the winding inner side-end portion11bin addition to the central portion of the positive electrode plate11in the longitudinal direction or instead of the central portion. The negative electrode lead20may be attached to the winding inner side-end portion12bin addition to the winding outer side-end portion12aor instead of the winding outer side-end portion12a.

The case body15is a metal container having a bottomed cylindrical shape. A gasket27is interposed between the case body15and the sealing body16to ensure sealing of the battery case. The case body15has, for example, a protrusion21which is formed by pressing the side surface from outside and which supports the sealing body16. The protrusion21is preferably annularly formed in the circumferential direction of the case body15and supports the sealing body16on its upper surface.

The sealing body16includes a filter22having a filter opening22a,valve bodies (a lower valve body23, an upper valve body25), an insulating member24, and a cap26having a cap opening26a.The valve bodies close the filter opening22aand fracture when heat generation caused by an internal short circuit or the like increases the internal pressure of the battery. The members that constitute the sealing body16have, for example, a disc shape or ring shape. The members other than the insulating member24are electrically connected to one another. The lower valve body23and the upper valve body25are connected to each other at their center portions, and the insulating member24is interposed between the peripheral portions of the lower valve body23and the upper valve body25. When heat generation caused by an internal short circuit or the like increases the internal pressure, for example, the lower valve body23fractures. This causes the upper valve body25to curve toward the cap26and come apart from the lower valve body23, which breaks the electrical connection between the lower valve body23and the upper valve body25.

Referring toFIG. 3toFIG. 7, the electrode body14, particularly the positive electrode plate11and the structure associated with the positive electrode plate11will be specifically described.

FIG. 3andFIG. 4are perspective views of the positive electrode plate11.FIG. 5is a view of the positive electrode plate11ofFIG. 3to which the positive electrode lead19is attached.FIG. 6is a sectional view taken along line A-A inFIG. 5.FIG. 3toFIG. 6illustrate the straightened positive electrode plate11. The right side of each figure corresponds to the winding outer side (winding end side) of the electrode body14, and the left side of each figure corresponds to the winding inner side (winding start side). As described above, the longitudinal direction of the positive electrode plate11corresponds to the winding direction γ of the electrode body14, and the width direction of the positive electrode plate11corresponds to the axial direction α of the electrode body14. A first end portion30aof a positive electrode core30in the longitudinal direction is located on the winding outer side of the electrode body14. A second end portion30bin the longitudinal direction is located on the winding inner side of the electrode body14.

The positive electrode plate11includes a strip-shaped positive electrode core30and a positive electrode active material layer31provided on at least one surface of the positive electrode core30. In this embodiment, the positive electrode active material layer31is provided on each surface of the positive electrode core30. The size of the positive electrode core30depends on, for example, the size of the battery, and the positive electrode core30is typically 300 mm to 800 mm long and 30 mm to 80 mm wide. The positive electrode core30is, for example, a foil made of a metal, such as aluminum, or a film having the surface layer made of the metal. The positive electrode core30is preferably a metal foil containing aluminum or an aluminum alloy as a main component. The thickness of the positive electrode core30is, for example, 10 μm to 30 μm.

The positive electrode active material layer31is preferably provided in substantially all parts of each surface of the positive electrode core30except for a bare part32described below. The positive electrode active material layer31preferably contains a positive electrode active material, a conductive material, and a binding material. As described below in detail, the positive electrode plate11can be produced by applying, to each surface of the positive electrode core30, a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binding material, and a solvent, such as N-methyl-2-pyrrolidone (NMP) and pressing each coating film.

Examples of the positive electrode active material include lithium-containing composite oxides containing transition metal elements, such as Co, Mn, and Ni. The lithium-containing composite oxide is preferably, but not necessarily, a composite oxide represented by general formula Li1+xMO2(where −0.2<x≤0.2, −0.1≤b ≤0.1, and M includes at least one of Ni, Co, Mn, and Al). Suitable examples of the composite oxide include Ni—Co—Mn-based lithium-containing composite oxides, and Ni—Co—Al-based lithium-containing composite oxides.

The conductive material is used to increase the electrical conductivity of the positive electrode active material layer31. Examples of the conductive material include carbon materials, such as carbon black (CB), acetylene black (AB), Ketjenblack, and graphite. These conductive materials may be used alone or in combination of two or more.

The binding material is used to maintain good conditions of contact between the positive electrode active material and the conductive material and to increase the strength of bonding of the positive electrode active material or the like to the surface of the positive electrode core30. Examples of the binding material include fluorocarbon resins, such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used together with, for example, carboxymethyl cellulose (CMC) or a salt thereof, or polyethylene oxide (PEO). These binding materials may be used alone or in combination of two or more.

As illustrated inFIG. 3andFIG. 4, the bare part32in which the surface of the core is exposed is formed in an end portion of the positive electrode core30in the width direction. The bare part32is a part to which the positive electrode lead19is to be connected and in which there is no positive electrode active material layer31and the surface of the core is not covered with the positive electrode active material layer31. The formation of the bare part32allows the positive electrode lead19to be directly connected to the positive electrode core30. The bare part32is formed to have a length of L32in the width direction of the positive electrode core30from an end of the positive electrode core30in the width direction. Hereinafter, the direction of the bare part32along the longitudinal direction of the positive electrode core30may be referred to as a transverse direction, and the direction of the bare part32along the width direction of the positive electrode core30may be referred to as a vertical direction for convenience of description.

The length L32of the bare part32in the vertical direction is preferably ½ or less of the width L30of the positive electrode core30, more preferably ⅓ or less of L30in order to increase the area of the positive electrode active material layer31as large as possible and thus increase the capacity of the battery. The length L32of the bare part32is still more preferably ⅓ to 1/10 of L30in view of, for example, high capacity, the attachability of the positive electrode lead19, and the current collecting performance of the positive electrode plate11. The length of the bare part32in the transverse direction is preferably similar to the width of the positive electrode lead19without hindering the attachment of the positive electrode lead19to the bare part32and is, for example, slightly longer than the width of the positive electrode lead19.

The bare part32may be formed by removing part of the positive electrode active material layer31after forming the positive electrode active material layer31in all parts of each surface of the positive electrode core30. As described below, the bare part32is preferably formed by application of no positive electrode mixture slurry to part of the positive electrode core30. For example, intermittent application of the positive electrode mixture slurry to form the bare part32can eliminate the process for removing the active material layer and can reduce material costs.

A plurality of the bare parts32may be formed on one surface of the positive electrode core30, but one bare part32is formed on one surface of the positive electrode core30in this embodiment. When a plurality of the positive electrode leads19is attached, the bare parts32as many as the leads are formed. The positive electrode active material layer31is provided on each surface of the positive electrode core30as described above, and one bare part32is also formed in each surface of the positive electrode core30in this embodiment. Since the positive electrode lead19is typically connected to one surface of the positive electrode core30by welding or the like, the bare part32may be formed on only one surface of the positive electrode core30even when the positive electrode active material layer31is provided on each surface of the positive electrode core30. However, the active material layer located on the surface opposite to the surface having the bare part32may inhibit, for example, connection of the positive electrode lead19to the bare part32. Thus, the bare part32is preferably formed on each surface of the positive electrode core30such that the bare parts32overlap each other in the thickness direction or the positive electrode core30.

The bare part32is formed at a position distant from the first end portion30aof the positive electrode core30in the longitudinal direction. The first end portion30acorresponds to the winding outer side-end portion11aof the positive electrode plate11in the electrode body14. The bare part32may be formed in each end portion of the positive electrode core30in the longitudinal direction, and preferably formed in a central portion of the positive electrode core30in the longitudinal direction in view of the current collecting performance of the positive electrode plate11. In other words, the bare part32is preferably formed at a position that is located at a substantially equal distance from the first end portion30ain the longitudinal direction and the second end portion30bin the longitudinal direction. In this case, the positive electrode active material layer31is provided on each surface of the bare part32in the transverse direction.

The positive electrode active material layer31includes a thin part35in at least part of a first region33aligned with the bare part32in the longitudinal direction of the positive electrode core30. The thin part35is thinner than a second region34, which is a region other than the first region33. In other words, the positive electrode active material layer31has two regions having a different thickness. The second region34may locally include a thin part having a small thickness as long as the average thickness of the thin part35is smaller than the average thickness of the second region34and, preferably, the maximum thickness of the thin part35is smaller than the minimum thickness of the second region34. When the thin part35is formed in the first region33, the thin part35absorbs a difference between the thickness of the positive electrode lead19and the thickness of the second region34and minimizes winding misalignment in the electrode body14.

Here, the first region33of the positive electrode active material layer31refers to a region that is aligned with the bare part32in the longitudinal direction of the positive electrode core30(positive electrode plate11) and that overlaps the bare part32in the longitudinal direction of the positive electrode core30. In this specification, a region that even slightly overlaps the bare part32in the longitudinal direction of the positive electrode core30is defined as the first region33. The second region34of the positive electrode active material layer31is a region that is out of alignment with the bare part32in the longitudinal direction of the positive electrode core30and that does not overlap the bare part32in the longitudinal direction. The thickness of the positive electrode active material layer31can be measured using a contact thickness gauge. The average thickness of the positive electrode active material layer31is calculated from the measurement values obtained by measuring the thickness at any ten points in a target region to be measured.

The thickness of the positive electrode active material layer31is preferably substantially uniform in the second region34, which is a region other than the first region33. The second region34is preferably as thick as possible in view of high capacity or other factors. The average thickness of the second region34is preferably, but not necessarily limited, 50 μm to 150 μm, more preferably 60 μm to 140 μm, and still more preferably 70 μm to 130 μm.

As the thickness of the positive electrode active material layer31increases, it is more difficult to stretch the electrode plate and it is easier to fracture the electrode plate. Therefore, the average thickness of the second region34is preferably 150 μm or less as described above and is typically smaller than the thickness of the positive electrode lead19. The second regions34each provided on each surface of the positive electrode core30preferably have substantially the same thickness, and the total thickness of the second regions34is, for example, 100 μm to 300 μm.

The average thickness of the thin part35is preferably 0.80 to 0.99 times, and more preferably 0.85 to 0.37 times the average thickness of the second region34. When the thickness ratio between the thin part35and the second region34is within this range, the winding misalignment of the electrode body14can be minimized efficiently while a decrease in the capacity of the battery is suppressed. In general, as the region (area) in which the thin part35is formed is smaller, the thin part35is preferably thinner and a suitable thickness ratio between the thin part35and the second region34is larger.

The mass per unit area of the thin part35is preferably smaller than the mass per unit area of the second region34. For example, the density of the thin part35is substantially the same as the density of the second region34, and the density of the positive electrode active material layer31is substantially uniform in all parts including the thin part35. In this embodiment, the coating amount of the positive electrode mixture slurry is different in the first region33and the second region34, and each coating film is pressed in the same conditions. The coating amount of the slurry in a region of the positive electrode core30corresponding to the first region33is smaller than that in a region corresponding to the second region34. In this case, the thickness of the first region33can be made smaller than the thickness of the second region34while the density of each region is substantially the same. The reason why a difference in thickness is generated between the regions when the coating films are pressed using a uniform roll may be that the amount of spring back of the coating film after pressing differs depending on the coating amount of the slurry. In other words, the amount of spring back in the first region33is smaller than that in the second region34even when the coating films are pressed into the same thickness.

It is also possible to cause the first region33and the second region34to have a different thickness by changing the conditions for pressing the coating film in each region while the coating amount of the positive electrode mixture slurry is the same in the first region33and the second region34. For example, it is possible to press the second region34more gently than to press the first region33. In this case, the mass per unit area of each region becomes substantially the same, and the density of the second region34becomes smaller than the density of the first region33. Since the density is preferably increased by strongly pressing the positive electrode active material layer31in view of the energy density of the battery, it is preferred to change the coating amount of the positive electrode mixture slurry as described above and press each coating film in the same conditions.

The thin part35may be formed only in the first region33on one surface of the positive electrode core30to which the positive electrode lead19is to be attached. The thin part35, however, is preferably formed in each first region33on each surface of the positive electrode core30. The thin parts35each formed on each surface of the positive electrode core30preferably overlap each other in the thickness direction of the positive electrode core30. The formation of the thin part35on each surface of the positive electrode core30makes it easy to absorb a difference between the thickness of the positive electrode lead19and the thickness of the second region34.

In the example illustrated inFIG. 3, the thin part35is formed in substantially ail parts of the first region33, and substantially all parts of the first region33are thinner than the second region34. The thickness of the thin part35is substantially uniform in all parts of the first region33. The positive electrode active material layer31has the thin part35in an end portion of the positive electrode core30in the width direction. The thin part35is formed in the longitudinal direction of the positive electrode core30so as to have a strip shape in plan view. A step is formed in the longitudinal direction of the positive electrode plate11and at the position of the boundary between the first region33(thin part35) and the second region34. The thickness of the thin part35may change in the longitudinal direction of the positive electrode core30. For example, the thin part35becomes thinner gradually or stepwisely at a distance closer to the bare part32from at least one of the first end portion30aof the positive electrode core30in the longitudinal direction and the second end portion30bof the positive electrode core30in the longitudinal direction.

In the example illustrated inFIG. 3, the thin part35is formed in substantially all parts of the first region33of each positive electrode active material layer31provided on each surface of the positive electrode core30. In other words, the area of the thin part35is maximum in the form illustrated toFIG. 3. In this case, the average thickness of the thin part35is preferably 0.90 to 0.99 times and more preferably 0.93 to 0.97 times the average thickness of the second region34.

In the example illustrated inFIG. 4, a thin part35is formed only on the winding outer side of the first region33with respect to the bare part32. The thin part35is formed in substantially all parts of the first region33(hereinafter may be referred to as a “winding outer-side first region”) located on the winding outer side with respect to the bare part32. On the winding inner side with respect to the bare part32, the thickness of the first region33is substantially the same as the thickness of the second region34. The thickness of the thin part35is substantially uniform in all parts of the winding outer-side first region, and a step is formed in the longitudinal direction of the positive electrode plate11and at the position of the boundary between the thin part35and the second region34. As in the form illustrated inFIG. 3, the thickness of the thin part35may change in the longitudinal direction of the positive electrode core30.

In the example illustrated inFIG. 4, the thin part35is formed in substantially all parts of the winding outer-side first region in the first region33of each positive electrode active material layer31provided on each surface of the positive electrode core30. In this case, the area of the thin part35is ½ of the area of the first region33. Since the absorption of the thickness of the positive electrode lead19is most efficiently carried out by the thin part35formed in the winding outer-side first region, the form illustrated toFIG. 4is preferred in order to increase the capacity and minimize winding misalignment. In this case, the average thickness of the thin part35is preferably 0.85 to 0.97 times and more preferably 0.90 to 0.95 times the average thickness of the second region34.

The thin part35is preferably formed at a position such that the thin part35overlaps the positive electrode lead19(bare part32) in the radial direction β of the electrode body14, and more preferably formed at a position such that the thin part35overlaps itself in the radial direction β on the winding outer side with respect to the positive electrode lead19. The thin part35may be formed, for example, in the range of substantially a half of the winding outer-side first region (e.g., a range from the bare part32to a middle point between the bare part32and the first end portion30ain the longitudinal direction) or in the range of substantially a half of the first region with the bare part32located in the range. The thin part35can also be selectively formed only at a position such that the thin part35overlaps the positive electrode lead19in the radial direction β of the electrode body14.

As illustrated inFIG. 5, the positive electrode lead19is connected to one of the bare parts32each formed on each surface of the positive electrode core30. The positive electrode lead19is attached to the bare part32by, for example, welding. An insulating tape36for covering the positive electrode lead19is preferably attached to the positive electrode plate11to which the positive electrode lead19has been welded. The insulating tape36is attached to a part of the positive electrode lead19that opposes the negative electrode plate12. In the example illustrated inFIG. 5, the insulating tape36is attached to cover a part of the positive electrode lead19connected to the bare part32and portions of the thin part35located on both sides of the bare part32in the transverse direction.

The insulating tape36is an adhesive tape in which an adhesive layer is formed on one surface of a resin film and which has high electrolyte solution resistance. The insulating tape36covers the positive electrode lead19and the bare part32and prevents generation of a row-resistance internal short circuit involving the flow of a large current upon contact between the negative electrode plate12and the positive electrode lead19or the positive electrode core30when the separator13fractures. To prevent such an internal short circuit, the insulating tape36is preferably attached to cover the bare part32to which the positive electrode lead19is not attached.

As illustrated inFIG. 6, the thickness T19of the positive electrode lead19is larger than the thickness of the positive electrode active material layer31(the thickness T34of the second region34). When the thickness T19is smaller than the thickness T34and the sum (T19+T36) of the thickness T19and the thickness T36of the insulating tape36is larger than the thickness T34, the electrode body14tends to undergo winding misalignment. However, when the thickness T19is larger than the thickness T34, an issue of winding misalignment becomes more significant. It is difficult to make the thickness T19of the positive electrode lead19smaller than the thickness of the positive electrode active material layer31in view of the current collecting performance of the positive electrode plate11and in order to, for example, suppress a fracture of the lead and suppress a fracture of the positive electrode plate11caused by an increased thickness of the positive electrode active material layer31. In other words, it is difficult to form the positive electrode active material layer31so as to have a thickness larger than the thickness T19of the positive electrode lead19.

The thickness T36of the insulating tape36is preferably small in order to minimize winding misalignment as long as the insulating tape36maintains a function of preventing a short circuit. In the example illustrated inFIG. 6, the sum (T35+T36) of the thickness T35of the thin part35and the thickness T36of the insulating tape36is smaller than the thickness T34of the second region34(T35+T36<T34). The insulating tape36is attached to cover portions of the thin part35located on both sides of the bare part32in the transverse direction. When T35+T36<T34, the portions of the thin part35to which the insulating tape36has been attached do not protrude further than the second region34, and it easy to reduce the influence of the thickness of the insulating tape36.

As illustrated inFIG. 7, the negative electrode plate12includes a strip-shaped negative electrode core40and a negative electrode active material layer41provided on at least one surface of the negative electrode core40. The size of the negative electrode core40depends on the size of the battery or the like, and the negative electrode core40is typically 350 mm to 900 mm long and 35 mm to 90 mm wide. The negative electrode core40is, for example, a foil made of a metal, such as copper, or a film having the surface layer made of the metal. The thickness of the negative electrode core40is, for example, 10 μm to 30 μm. The negative electrode active material layer41is preferably provided in substantially all parts of each surface of the negative electrode core40except for a bare part42described below. The negative electrode active material layer41preferably contains a negative electrode active material and a binding material. The negative electrode plate12is produced, for example, by applying, to each surface of the negative electrode core40, a negative electrode mixture slurry containing a negative electrode active material, a binding material, and water and pressing each coating film.

The negative electrode active material is any active material that can reversibly intercalate and deintercalate lithium ions. Examples of the negative electrode active material include carbon materials, such as natural graphite and artificial graphite, metals, such as Si and Sn, to be alloyed, with lithium, alloys and oxides containing metal elements, such as Si and Sn. These materials way be used alone or in a mixture of two or more. Examples of the binding material in the negative electrode active material layer41include fluorocarbon resins, PAN, polyimide resins, acrylic resins, and polyolefin resins, which are the same as those for the positive electrode plate11. When the negative electrode mixture slurry is prepared by using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like can be used.

In the example illustrated inFIG. 7, a bare part42is located in the first end portion40aof the negative electrode core40in the longitudinal direction that corresponds to the winding outer side-end portion12aof the negative electrode plate12in the electrode body14and formed over the full width of the negative electrode core40. The bare part42is a part in which the surface of the core is exposed and to which a negative electrode lead20is to be connected. The negative electrode active material layer41is formed on each surface of the negative electrode core40except for the bare part42so as to have a substantially uniform thickness. The position at which the bare part42is formed or the like is not limited to the position or the like illustrated inFIG. 7. The bare part42may be formed in a second end portion40bof the negative electrode core40in the longitudinal direction or may be formed in a central portion of the negative electrode core40in the longitudinal direction. When the bare part42is formed in part of the negative electrode core40in the width direction so as to be distant from a first end portion40ain the longitudinal direction, a thin part, that is thinner than other regions is preferably formed in a first region of the negative electrode active material layer41aligned with the bare part42in the longitudinal direction of the negative electrode core40, as in the positive electrode plate11.

Referring toFIG. 8andFIG. 9, an example method for producing the positive electrode plate11will be described below in detail.FIG. 8is a plan view illustrating a long body11zof the positive electrode plate (hereinafter referred to simply as a “long body11z”).FIG. 9is a sectional view taken along line B-B inFIG. 8. The long body11zis a long body that is to be divided into a plurality of positive electrode plates11when cut along intended cut lines X, Y1, and Y2. The parts of the long body11zthat correspond to the positive electrode active material layer31, the bare part32, the first region33, and the second region34of the positive electrode plate11obtained when the long body11zis cut along the intended cut lines are respectively defined as a positive electrode active material layer31z,a bare part32z,a first region33z,and a second region34z.

As illustrated inFIG. 8andFIG. 9, the long body11zhas the positive electrode active material layer31z(the first region33zand the second region34z) on each surface of a long body30zof a positive electrode core (hereinafter referred to simply as a “long body30z”). The positive electrode active material layer31zis formed by applying a positive electrode mixture slurry to the long body30zand pressing the coating film. The positive electrode mixture slurry contains a positive electrode active material, a conductive material, a binding material, a solvent, and the like as described above. The coating film formed by application of the positive electrode mixture slurry is subjected to, for example, heat drying and then pressed with a roll to form the positive electrode active material layer31z.The negative electrode plate12can be produced in the same manner as for the positive electrode plate11except that the negative electrode mixture slurry is used instead of the positive electrode mixture slurry and that no thin part35is formed.

The bare part32zin which the surface of the long body30zis exposed is preferably formed by intermittent application of the positive electrode mixture slurry such that no positive electrode mixture slurry is applied to parts of the long body30zin the longitudinal direction during the formation of the positive electrode active material layer31z.In other words, the bare part32zis formed as a non-coated part without coating of the positive electrode mixture slurry. In the example illustrated inFIG. 8, the bare parts32zare located in a central portion of the long body30zin the width direction and formed at substantially regular intervals in the longitudinal direction of the long body30z.The long body30zincludes two positive electrode cores30in the width direction. The bare part32zis formed as bare parts of two positive electrode plates11so as to have an area that is twice the area of the bare part32.

The bare part32zis, for example, symmetric with respect to the center (intended cut line Y1) of the long body30zin the width direction. The first region33zof the positive electrode active material layer31zaligned with the bare part32zin the longitudinal direction of the long body30zis also symmetric with respect to the center in the width direction. On each, side of the first region33zin the width direction, the positive electrode mixture slurry is continuously applied onto the long body30z.to form the second region34zof the positive electrode active material layer31z.

In the example illustrated inFIG. 8, the long body11zincluding the positive electrode active material layer31zon each surface of the long body30zis cut along the intended cut line Y1at the center in the width direction, and unnecessary edges of the long body11zare cut along the intended cut lines Y2to produce long bodies each having a width equivalent to the width of one positive electrode plate11. The long bodies are then cut in the width direction along the intended cut lines X to produce positive electrode plates11.

The positive electrode active material layer31zhas a plurality of strip-shaped regions (the first region33z,the second region34z) in the longitudinal direction of the long body11z.The plurality of strip-shaped regions each has a different thickness. The first region33zis thicker than the second region34z.The first region33zand the second region34zcan be formed by using a slurry coater having a plurality of application members from which the positive electrode mixture slurry is applied independently. An example application member is a nozzle having a discharge port. The slurry coater has, for example, a valve with which on/off of slurry application in each application site, the slurry coating amount, and the like can be controlled independently.

The first region33zis formed by, for example, intermittent application of the positive electrode mixture slurry from an application member (hereinafter referred to as a “first application member”) disposed above in a central portion of the long body30zin the width direction. The bare part32zis formed when the application of the slurry is terminated. The first region33zand the bare part32zcan be alternately formed at substantially regular intervals by repeating on and off of slurry application at regular intervals. The second region34zis formed by, for example, continuous application of the slurry from an application member (hereinafter referred to as a “second application member”) disposed adjacent to the first application member from which the slurry for forming the first region33zis applied. In general, the application of the slurry onto the long body30zis carried out while the long body30zis continuously conveyed in the longitudinal direction with the positions of the application members fixed.

In the process for applying the positive electrode mixture slurry, the slurry coating amount from the first application member is smaller than the slurry coating amount from the second application member. The slurry coating amount from the first application member is adjusted to, for example, 0.80 to 0.99 times the slurry coating amount from the second application member. The conditions for pressing the coating film are the same in both regions. Due to this process, the first region33zbecomes thinner than the second region34z,and the thin part35zis formed in the first region33z.In addition, the density of the thin part35zbecomes substantially equal to the density of the second region34z.

The slurry coating amount from the first application member may be set at a constant value or varied in continuous application. When the slurry coating amount is set at a constant value, the thin part35zcan be formed in substantially all parts of the first region33z.When the slurry coating amount is varied, for example, the thin part35zcan be formed only on the winding outer side of the positive electrode plate11with respect to the bare part32, and the thickness of the thin part35zcan be changed. The slurry coating amount from the second application member is preferably set at a constant value.

The first application member and the second application member are disposed above the long body30zthat is continuously conveyed in the longitudinal direction and are out of alignment with each other in the width direction of the long body30zsuch that these members do not interfere with each other. In other words, one of the first application member and the second application member is disposed upstream in the conveyance direction of the long body30z,and the other is disposed downstream in the conveyance direction.

The discharge port of the first application member and the discharge port of the second application member do not overlap each other in the longitudinal direction (conveyance direction) of the long body30z, and the application members may be disposed such that the end portions of the discharge ports are aligned with each other in the longitudinal direction. Alternatively, the application members may be disposed such that parts of the discharge ports overlap each other in the longitudinal direction of the long body30z,that is, parts of the discharge ports are aligned with each other in the longitudinal direction. Since the slurry coating amount tends to decrease at the end portion of the discharge port, the layer thickness may be significantly reduced at the position of the boundary between the first region33zand the second region34zin the former arrangement. According to the latter arrangement, it is easy to minimize such a reduction in layer thickness by controlling the degree of overlap of the discharge ports in a suitable range.

According to the non-aqueous electrolyte secondary battery10having the above-described configuration, the thin part35formed in the first region33of the positive electrode active material layer31can absorb a difference between the thickness of the positive electrode lead19and the insulating tape36and the thickness of the second region34. Since the capacity of the battery is increased by increasing the area of the positive electrode active material layer31as large as possible, the winding misalignment of the electrode body14can be minimized sufficiently even when the positive electrode lead19is connected to the bare part32formed in part of the positive electrode core30in the width direction.

Table 1 indicates an example effect of minimizing winding misalignment in the non-aqueous electrolyte secondary battery10(Example). In Table 1, the case where the first region of the positive electrode active material layer has no thin part is described as a comparison. The wound-type electrode bodies of Example and Comparative Example are produced in the same conditions using the same positive electrode plate, the same negative electrode plate, the same separator, and the same electrode plate lead, except for the presence or absence of the thin part. The winding misalignment is evaluated by determining the meandering amount of the positive and negative electrode plates that run during winding. When the meandering amount of the positive electrode plate and the negative electrode plate is within 0.6 mm, it assumed that there is no winding misalignment. When the meandering amount of at least one of the positive electrode plate and the negative electrode plate exceeds 0.6 mm, it assumed that there is winding misalignment. As indicated in Table 1, the winding misalignment can be minimized by forming the thin part.

The details of Example and Comparative Example are as described below. The evaluation of winding misalignment was carried out for 20 electrode bodies in each of Example and Comparative Example. The thickness of the positive electrode active material layer is a mean of the values obtained by measuring the thickness of 10 positive electrode plates out of 20 electrode bodies.

(1) Positive Electrode Plate

Positive electrode core: aluminum foil, 661 mm long, 58 mm wide, 0.15 mm thickBare part: formed in an end portion of the positive electrode core in the width direction and in a central portion of the positive electrode core in the longitudinal direction.Positive electrode active material layer: including a lithium-nickel composite oxide, acetylene black, and polyvinylidene fluoride and formed on each surface of the positive electrode core.Average thickness of first region (thin part) of positive electrode active material layer: 130 μmAverage thickness of second region of positive electrode active material layer: 140 μm
(The positive electrode active material layer of Comparative Example is formed to have the same thickness as the second region)Ratio of thickness of first region to thickness of second region (first region/second region): 0.96
(2) Negative Electrode PlateNegative electrode core: copper foil, 720 long, 53 mm wide, 0.1 mm thickBare part: formed over the full width of the negative electrode core in a first end portion (winding outer side-end portion) of the negative electrode core in the longitudinal direction.Negative electrode active material layer: including graphite, styrene-butadiene rubber, and carboxymethyl cellulose and formed on each surface of the negative electrode core.Average thickness of negative electrode active material layer: 160 μm
(3) Separator: polyethylene microporous membrane 16 μm thick
(4) Positive electrode lead: 3 mm wide, 0.15 mm thick
(5) Negative electrode lead: 3 mm wide, 0.15 mm thick
(6) Electrode body: (diameter 18 mm) produced by winding the positive electrode plate in which the positive electrode lead has been welded to the bare part of the positive electrode core, and the negative electrode plate in which the negative electrode lead has been welded to the bare part of the negative electrode core, with the separator interposed between the positive electrode plate and the negative electrode plate.

REFERENCE SIGNS LIST