WO2013031213A1

WO2013031213A1 - Electrode plate for non-aqueous secondary battery and non-aqueous secondary battery using same

Info

Publication number: WO2013031213A1
Application number: PCT/JP2012/005442
Authority: WO
Inventors: 元貴衣川; 伊達　健二; 了介大前; 智文柳; 渡邉　耕三; 藤原　勲
Original assignee: パナソニック株式会社
Priority date: 2011-08-29
Filing date: 2012-08-29
Publication date: 2013-03-07

Abstract

An electrode plate for a non-aqueous secondary battery. Said electrode plate is provided with a rectangular collector and a mixture layer that is formed on the surface of the collector and contains a first active material. The mixture layer has: a first edge section that runs along one edge of the collector; a second edge section on the opposite side from the first edge section; a third edge section that runs along an edge of the collector perpendicular to the aforementioned one edge; a fourth edge section on the opposite side from the third edge section; and a main section consisting of the area that is not part of the first through fourth edge sections. At least one prescribed edge section selected from the group consisting of the first through fourth edge sections is thinner than the main section of the mixture layer. The surface of the prescribed edge section(s) is covered by a surface layer containing a second active material that is more reactive with respect to lithium than the first active material is.

Description

Non-aqueous secondary battery electrode plate and non-aqueous secondary battery using the same

The present invention relates to an electrode plate for a non-aqueous secondary battery represented by a lithium ion battery and a non-aqueous secondary battery using the same.

In recent years, the use of non-aqueous secondary batteries such as lithium ion secondary batteries has been expanding as power sources for electric vehicles. A typical lithium ion secondary battery uses a carbon material that can store and release lithium as a negative electrode active material, and a lithium-containing composite oxide such as LiCoO ₂ as a positive electrode active material. As a result, a high voltage and high capacity secondary battery is realized. However, with the recent increase in demand for power sources for electric vehicles, further improvements in capacity, long life, and safety are required.

In order to meet the above requirements, various improvements of the positive electrode and the negative electrode have been studied. One of them is a method in which a coating material having a mixture layer containing an active material is applied to the surface of a current collector, and then a coating material having a different composition is applied as a surface layer. At this time, it is possible to extend the life and improve the safety depending on the characteristics of the applied surface layer (see Patent Documents 1 and 2).

On the other hand, when applying a paint containing an active material to the current collector, the end of the mixture layer tends to rise due to the surface tension of the coating film. Therefore, when the end portions of the positive electrode and the negative electrode overlap, the separator is pressed, causing an internal short circuit. Then, the method of preventing an internal short circuit is considered by restrict | limiting the position of the swelling of an edge part (refer patent document 3).

JP 2005-183179 A JP 2010-97720 A JP 2010-262773 A

As described above, even when the rising position of the end portion is regulated, the distance between the positive electrode and the negative electrode is close at the rising end portion. Therefore, electric charges may concentrate on the end portion of the mixture layer, and lithium may be deposited. Such lithium deposition causes deterioration of charge / discharge cycle characteristics.

In view of the above, one aspect of the present invention includes a rectangular current collector and a mixture layer including a first active material formed on a surface of the current collector, and the mixture layer includes the current collector. A first end along one end of the electrical current body, a second end opposite to the first end, a third end along the other end perpendicular to the one end of the current collector, At least one selected from the group consisting of the first to fourth ends, and a fourth end opposite to the third end and a main portion other than the first to fourth ends. The thickness of one predetermined end is smaller than the thickness of the main part of the mixture layer, and the surface of the predetermined end is a surface layer containing a second active material having a higher reactivity with lithium than the active material It is related with the electrode plate for non-aqueous secondary batteries covered.

Another aspect of the present invention includes an electrode group, a nonaqueous electrolyte, and an exterior body that houses the electrode group together with the nonaqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, the positive electrode, and the negative electrode. The positive electrode and the negative electrode are laminated or wound via the porous insulating layer, and at least one of the positive electrode and the negative electrode is the above-described porous insulating layer. The present invention relates to a non-aqueous secondary battery which is an electrode plate for a non-aqueous secondary battery.

According to the present invention, since the thickness of at least one end portion of the mixture layer is smaller than the thickness of the main portion of the mixture layer, the concentration of charges on the end portion is unlikely to occur. Therefore, lithium is hardly deposited at the end. Therefore, a non-aqueous secondary battery excellent in charge / discharge cycle characteristics can be obtained.

While the novel features of the invention are set forth in the appended claims, the invention will be further described by reference to the following detailed description, taken in conjunction with the other objects and features of the invention, both in terms of construction and content. It will be well understood.

1 is a partially cutaway perspective view of a nonaqueous secondary battery in a first embodiment of the present invention. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in 1st Embodiment of this invention. It is a schematic diagram of the front of the electrode plate. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in 2nd Embodiment of this invention. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in 3rd Embodiment of this invention. It is a schematic diagram of the front of the electrode plate for non-aqueous secondary batteries in 4th Embodiment of this invention. 6 is a schematic view of a cross section of a nonaqueous secondary battery electrode plate of Comparative Example 1. FIG. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in the 1st reference form of this invention. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in the 2nd reference form of this invention. It is a partial schematic diagram of the surface of the same electrode plate. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in the modification of 2nd reference form. It is a partial schematic diagram of the surface of the same electrode plate. It is a schematic diagram of the cross section of the electrode plate for non-aqueous secondary batteries in another modification of the second reference embodiment. It is a partial schematic diagram of the surface of the same electrode plate.

The electrode plate for a non-aqueous secondary battery of the present invention comprises a rectangular current collector and a mixture layer containing a first active material formed on the surface of the current collector. The mixture layer includes a first end along one end of the current collector, a second end opposite to the first end, and a third end along the other end perpendicular to the one end of the current collector. An end portion, a fourth end portion opposite to the third end portion, and a main portion other than the first to fourth end portions. That is, the main portion is a portion excluding the end portions along the four sides of the rectangular mixture layer.

The rectangle may be a long and narrow strip rectangle. Further, the rectangle does not mean only a perfect rectangle but includes a shape close to a rectangle.

The mixture layer is obtained, for example, by mixing the first active material with a liquid dispersion medium together with optional components to prepare a mixture paint, applying the paint to the surface of the current collector, and drying the mixture. Can do. Examples of optional components include a binder, a conductive agent, and a thickener.

Each end mentioned above refers to a portion having a width of 20 mm or less (for example, 10 mm or less) from the outermost end. The extreme end corresponds to the position at which the mixture paint is applied to the current collector or the position at which the application is completed.

Here, the thickness of the predetermined end portion of the mixture layer is smaller than the thickness of the main portion of the mixture layer, and the surface of the predetermined end portion is more reactive with lithium than the first active material. It is covered with a surface layer containing a high second active material. However, the predetermined end is at least one end selected from the group consisting of the first to fourth ends. That is, the predetermined end may be any one of the first to fourth ends, or may be all of the first to fourth ends, and the first end and the second end. It may be a set, a set of the third end and the fourth end, or another set.

The surface layer can be obtained, for example, by mixing the second active material together with an optional component with a liquid dispersion medium to prepare a surface layer coating material, applying the coating material to the surface of the mixture layer, and drying. it can. Examples of optional components include a binder, a conductive agent, and a thickener.

Note that each of the first active material and the second active material is a material that can electrochemically react with lithium, for example, a material capable of reversibly occluding and releasing lithium ions.

As described above, the thickness of at least one end of the mixture layer is made thinner than the thickness (main part) other than the end of the mixture layer, and the surface of the end includes the second active material. By covering with the surface layer, the reactivity of the mixture layer can be smoothed over the entire mixture layer. Specifically, the charge concentration can be prevented only by making the thickness of the end portion of the mixture layer thinner than the thickness of the main portion, but the capacity of the end portion is reduced. On the other hand, by covering the surface of the end with a surface layer having high reactivity with lithium, the capacity of the end is supplemented and the acceptability of lithium ions at the end is improved. Thereby, it is considered that precipitation of lithium can be suppressed while preventing concentration of electric charges at the end portion of the mixture layer. Therefore, the charge / discharge cycle characteristics can be improved.

It should be noted that the surface layer may be a layer that is more excellent in lithium ion acceptability than the mixture layer and can suppress the precipitation of lithium. Therefore, the modified example of the above configuration does not necessarily include the second active material. In this case, the surface layer may be a layer containing alumina, magnesia, silica, titania or the like.

It is preferable that the thickness of the predetermined end portion becomes smaller toward the endmost portion of the predetermined end portion. Thereby, the effect of smoothing the reactivity (especially the reactivity at the end) of the mixture layer is increased.

The surface layer may include an end corresponding portion that covers the surface of the predetermined end portion, and a main portion corresponding portion that covers the surface of the main portion of the mixture layer. That is, the surface layer may cover not only the end portion of the mixture layer but also the entire mixture layer or, for example, 40% or more of the surface of the mixture layer. At this time, the thickness of the end corresponding part is preferably larger than the thickness of the main part corresponding part. This makes it easy to control the balance between the lithium ion acceptability at the end of the mixture layer where lithium is likely to precipitate and the lithium ion acceptability at the main part.

It is preferable that the thickness of the end portion corresponding portion of the surface layer is increased toward the end of the predetermined end. Thereby, since the lithium ion acceptance property of a predetermined edge part becomes large as it goes to the end part, the effect of smoothing the reactivity (especially the reactivity in an edge part) of a mixture layer becomes larger.

It is preferable that the surface layer covers the surface of the predetermined end portion and covers at least a part of the surface of the current collector. Thereby, the edge part of a mixture layer becomes difficult to drop | omit from a collector at the time of charging / discharging.

The maximum height roughness Rmax at the interface between the main part of the mixture layer and the main part corresponding part of the surface layer is preferably 3 to 25 μm. The thickness of the main part corresponding part is preferably 3 to 20 μm. Thereby, the adhesion strength between the mixture layer and the surface layer can be increased, and more excellent charge / discharge cycle characteristics can be ensured. Moreover, since it is suppressed that a mixture layer is exposed from a surface layer, an internal short circuit becomes very difficult to generate | occur | produce.

Here, the maximum height roughness Rmax is obtained by extracting only the reference length from the roughness curve in the direction of the average line, and setting the interval between the peak line and the valley line of the extracted part in the direction of the vertical magnification of the roughness curve. Measured and expressed in micrometer μm.

As mentioned above, it is desirable that the mixture layer is not exposed from the surface layer from the viewpoint of enhancing the effect of suppressing the internal short circuit. However, according to the present invention, it is possible to obtain a sufficient effect of suppressing the internal short circuit regardless of whether or not the mixture layer is exposed. Rather, from the viewpoint of improving productivity, it may be desirable that a part of the main part of the mixture layer is exposed from the part corresponding to the main part of the surface layer. Specifically, the speed at which the non-aqueous electrolyte is impregnated in the mixture layer becomes faster when the mixture layer is exposed.

In order to expose a part of the main part of the mixture layer from the main part corresponding part of the surface layer, for example, a plurality of through holes may be scattered in the main part corresponding part. Such a through-hole can be easily formed by enclosing a sufficient amount of bubbles in the coating material for forming the surface layer and rupturing the bubbles in the state of the coating film. Or you may expose the convex part of a mixture layer from a surface layer by forming an unevenness | corrugation in a mixture layer so that Rmax may exceed 25 micrometers, for example.

The ratio of the area where the main part is exposed to the area of the main part (exposure degree) is preferably 60% or less, and more preferably 1 to 10%. By setting the degree of exposure within the above range, it is possible to increase the speed at which the nonaqueous electrolyte is impregnated in the mixture layer at the time of manufacturing the battery while maintaining the high effect of suppressing the internal short circuit.

As a preferred embodiment of the electrode plate of the present invention, the first active material is a carbon material capable of reversibly occluding and releasing lithium ions, and the second active material is capable of reversibly occluding and releasing lithium ions. The case where it is a lithium titanium complex oxide is mentioned. Such an electrode plate is useful as a negative electrode for a lithium ion secondary battery.

The non-aqueous secondary battery of the present invention includes an electrode group, a non-aqueous electrolyte, and an exterior body that houses the electrode group together with the non-aqueous electrolyte. The electrode group includes a positive electrode, a negative electrode, and a porous insulating layer interposed therebetween. The positive electrode and the negative electrode are laminated or wound through a porous insulating layer. Here, at least one of the positive electrode and the negative electrode is the electrode plate for a non-aqueous secondary battery.

The combination of the first active material and the second active material is not particularly limited as long as the lithium active material acceptability of the second active material is higher than that of the first active material. As the first active material and the second active material, nickel-based composite oxide, cobalt-based composite oxide, cobalt acid nanoparticles, cobalt-based oxynitride, manganese-based composite oxide, chromium-based composite oxide, iron phosphate It is possible to use a system composite oxide, a vanadium system composite oxide, a carbon material (graphite, hard carbon, etc.), a titanium system composite oxide, a tin system material, a silicon system material, or metallic lithium.

Hereinafter, the present invention will be described based on embodiments with reference to the drawings. However, the following embodiments do not limit the present invention.

(First embodiment)
FIG. 1 is a perspective view in which a part of a cylindrical lithium ion secondary battery 11 which is an example of a non-aqueous secondary battery is cut away.

The cylindrical lithium ion secondary battery 11 includes an electrode group 4 configured by winding a positive electrode 1 and a negative electrode 2 in a spiral shape through a separator 3 that is a porous insulating layer. The electrode group 4 is accommodated in a state of being insulated from the battery case 5 by an insulating plate 6 inside a bottomed cylindrical battery case 5 as an exterior body. On the other hand, a negative electrode lead (not shown) led out from the lower part of the electrode group 4 is connected to the bottom of the battery case 5. The positive electrode lead 8 led out from the upper part of the electrode group 4 is connected to a sealing plate 9 having a positive electrode terminal 9a. After the electrode group 4 is accommodated in the battery case 5, a predetermined amount of nonaqueous electrolyte is injected into the battery case 5. Thereby, the nonaqueous electrolyte is impregnated in the gaps of the electrode group 4 and the gaps of the mixture layer and the separator. The opening of the battery case 5 is sealed by a sealing plate 9 having a gasket 10 attached to the periphery. The open end of the battery case 5 is bent inward and is crimped to the peripheral edge (gasket 10) of the sealing plate 9.

FIG. 2 is a schematic diagram of a cross section of the negative electrode 2 in the present embodiment. Furthermore, FIG. 3 is a schematic diagram of the front surface of the negative electrode 2 in the present embodiment.

The negative electrode 2 includes a strip-shaped rectangular negative electrode current collector 12 and a negative electrode mixture layer 13 formed on the surface thereof. The negative electrode mixture layer 13 includes a first end 13 a along the short direction of the current collector 12, a second end 13 b opposite to the first end 13 a, and a first end along the longitudinal direction of the current collector 12. It is a rectangle having a three end portion 13c and a fourth end portion 13d opposite to the third end portion 13c. The portion other than the first to fourth end portions of the mixture layer 13 is a main portion 13A. The negative electrode 2 is wound so that the first end portion 13a side of the mixture layer 13 is on the outer peripheral side. In the vicinity of the first end portion 13a, the negative electrode lead 7 is bonded to the negative electrode current collector 12.

Here, the first end portion 13a and the second end portion 13b are predetermined end portions having a thickness smaller than that of the main portion 13A of the mixture layer. The thickness of the 1st end part 13a and the 2nd end part 13b is thin as it goes to the endmost part of each end part. The surfaces of the first end portion 13a and the second end portion 13b are covered with the surface layer 14 together with the surface of the main portion 13A. The thickness of the surface layer 14 is uniform, and the entire surface of the negative electrode mixture layer 13 is covered with the surface layer 14.

The negative electrode mixture layer 13 includes, for example, a carbon material or a silicon-based material capable of reversibly occluding and releasing lithium ions as the first active material. Examples of the carbon material include graphite (various natural graphite and artificial graphite), hard carbon, and soft carbon. Examples of the silicon-based material include silicon oxide (SiOx, where 0.1 ≦ x ≦ 1.8), silicon alloy (such as Ti—Si alloy), and the like. Further, the negative electrode mixture layer 13 may contain a fluorine resin such as polyvinylidene fluoride (PVdF), rubber particles such as a styrene-butadiene copolymer (SBR), and a cellulose resin such as carboxymethyl cellulose (CMC) as a binder. . From the viewpoint of improving the lithium ion acceptability, it is preferable to use SBR and CMC in combination. Further, the negative electrode mixture layer 13 can include carbon black, carbon nanotube, VGCF, and the like as a conductive material. As carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and the like can be used.

The surface layer 14 includes, for example, a lithium titanium composite oxide capable of reversibly occluding and releasing lithium ions as the second active material. As the lithium titanium composite oxide, for example, Li ₄ Ti ₅ O ₁₂ having a spinel structure and a modified product thereof are preferable, but not particularly limited. The modified products of Li ₄ Ti ₅ O _12, a material part of the Ti and / or Li of the Li ₄ Ti ₅ O ₁₂ is replaced with another element. Examples of the other element include at least one selected from the group consisting of Ni, Co, Mn, Fe, Al, Mg, and Cr. The ratio of elements substituted for Ti and / or Li is preferably 20 atomic% or less of the total of Ti sites and Li sites.

The surface layer 14 may also contain a binder as described above. By making the average particle size of the second active material smaller than the average particle size of the first active material and making the specific surface area of the second active material larger than the specific surface area of the first active material, In addition, the contact area between the negative electrode mixture layer 13 and the negative electrode current collector 12 is increased, and the binding property between them is increased.

Here, the average particle diameter D1 of the first active material is preferably 2 to 50 μm. The average particle diameter D2 (D1> D2) of the second active material is preferably 0.5 to 5 μm. The ratio of D1 / D2 is preferably 4 to 10. D1 and D2 are median diameters corresponding to a cumulative volume of 50% in the volume-based particle size distribution.

As described above, the mixture layer 13 is prepared by mixing the first active material together with an optional component with a liquid dispersion medium to prepare a mixture paint, applying the paint onto the surface of the current collector, and drying the mixture. Can be obtained. The thickness of the mixture layer is, for example, 30 to 150 μm. For the negative electrode current collector, for example, a copper foil or copper alloy foil having a thickness of 5 to 25 μm is used. The coated film after drying may be rolled. Or you may transfer to the formation process of the following surface layers 14, without drying the coating film of mixture paint.

The surface layer 14 can be obtained by mixing the second active material together with an optional component with a liquid dispersion medium to prepare a surface layer coating material, applying the coating material to the surface of the mixture layer, and drying. . Thereafter, the surface layer 14 may be rolled together with the mixture layer 13.

Preparation of the mixture paint and the surface layer paint is carried out by dispersing the material in a dispersion medium such as N-methyl-2-pyrrolidone (NMP) using a dispersing machine such as a planetary mixer. The viscosity of each paint is adjusted so as to be optimal for application to the current collector 12 or the mixture layer 13. Application of each paint may be performed by a die coater, for example.

The maximum height roughness Rmax of the interface between the mixture layer 13 and the surface layer 14 is set to, for example, 3 to 25 μm, and further 5 to 20 μm. The maximum height roughness Rmax corresponds to the distance in the thickness direction between the interface farthest from the current collector 12 and the interface closest to the current collector 12 among the interface between the mixture layer 13 and the surface layer 14. . By setting the maximum height roughness Rmax in the above range, the anchor effect in adhesion between the mixture layer 13 and the surface layer 14 is increased, and the mixture layer 13 is suppressed from being exposed from the surface layer 14. Internal short circuit is extremely difficult to occur. In this case, by setting the thickness of the surface layer 14 to 3 to 20 μm, further 5 to 15 μm, the adhesion strength between the mixture layer 13 and the surface layer 14 can be further increased, and the battery capacity can be secured. It becomes easy.

On the other hand, the structure of the mixture layer 13 and the surface layer 14 and the maximum height roughness Rmax of these interfaces may be set so that a part of the mixture layer 13 is exposed through the surface layer 14. Thereby, the impregnation property of the nonaqueous electrolyte to the mixture layer 13 can be improved. However, the ratio of the area where the main part is exposed to the area of the main part of the mixture layer 13 (exposure degree) is preferably 60% or less, and more preferably 1 to 10%.

For example, a part of the mixture layer 13 can be exposed by providing an outward projecting portion on the surface of the mixture layer 13 and passing the projecting portion through the surface layer 14. In this case, it is preferable that the maximum height roughness Rmax of the interface between the mixture layer 13 and the surface layer 14 is set to be larger than 25 μm, and more preferably Rmax is set to 30 to 60 μm by providing the protruding portion. . From the viewpoint of sufficiently increasing the impregnation property of the nonaqueous electrolyte, the diameter of the protrusion is preferably 20 to 100 μm at the center height.

A part of the mixture layer 13 may be exposed by interspersing a plurality of through holes in the surface layer 14. The through-hole can be easily formed by enclosing a sufficient amount of bubbles in the surface layer paint. The diameter of the through hole may be, for example, 20 μm or less, but may be, for example, 20-100 μm from the viewpoint of sufficiently enhancing the impregnation property of the nonaqueous electrolyte.

The positive electrode 1 has the same shape as the negative electrode 2 and includes a strip-shaped rectangular positive electrode current collector and a positive electrode mixture layer formed on the surface thereof. The positive electrode mixture layer includes a first end along the short side direction of the current collector, a second end opposite to the first end, a third end along the longitudinal direction of the current collector, A rectangular shape having a fourth end opposite to the three ends. A positive electrode lead 8 is joined to the positive electrode current collector.

As the positive electrode current collector, for example, an aluminum foil, an aluminum alloy foil, a nickel foil, or a nickel alloy foil having a thickness of 5 μm to 30 μm can be used. The positive electrode mixture paint applied to the surface of the positive electrode current collector is prepared, for example, by mixing a positive electrode active material, a conductive material, and a binder together with a dispersion medium using a disperser such as a planetary mixer. The mixture paint is applied to the positive electrode current collector using, for example, a die coater. Then, the positive electrode 1 is obtained by drying and then rolling the coating film.

The positive electrode mixture layer is, for example, a nickel composite oxide, a cobalt composite oxide, a manganese composite oxide, a cobalt acid nanoparticle, a cobalt oxynitride, a chromium composite oxide, or phosphoric acid as a positive electrode active material. Includes iron-based composite oxides, vanadium-based composite oxides, and the like. Examples of the nickel-based composite oxide include lithium nickelate and materials obtained by substituting nickel of lithium nickelate with other elements. Examples of the cobalt-based composite oxide include a material in which aluminum or magnesium is dissolved in lithium cobaltate or lithium cobaltate. Examples of the manganese-based composite oxide include lithium manganate having a spinel structure.

The positive electrode mixture layer can contain a binder and a conductive material as optional components. As the binder, polyvinylidene fluoride (PVdF), a modified polyvinylidene fluoride, polytetrafluoroethylene (PTFE), rubber particles containing an acrylate unit, or the like can be used. As the conductive material, the carbon black and various graphites already described can be used.

The negative electrode active material, the positive electrode active material, the negative electrode binder, the positive electrode binder, the negative electrode conductive material, and the positive electrode conductive material may be used singly or in combination. Also good.

The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the electrolyte salt, for example, various lithium compounds such as LiPF ₆ and LiBF ₄ can be used. As the non-aqueous solvent, for example, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC) and the like can be used. In addition, an additive such as vinylene carbonate (VC) or cyclohexylbenzene (CHB) may be used in order to form a film on the surface of the positive electrode or the negative electrode or to ensure stability during overcharge. Any one of the electrolyte salt and the non-aqueous solvent may be used alone, or a plurality of them may be used in combination.

As the separator 3 that is a porous insulating layer, a separator that can be used as a separator for a non-aqueous secondary battery can be used without particular limitation. For example, a microporous film formed of an olefin resin such as polyethylene or polypropylene is generally used alone or in an improved manner. The thickness of the separator is, for example, 10 to 25 μm.

In the non-aqueous secondary battery having the above-described configuration, the negative electrode lead 7 is joined to the exposed portion of the negative electrode current collector 12 on the outer peripheral side in the electrode group 4. Therefore, electric charges are particularly likely to concentrate on the first end portion 13a of the negative electrode mixture layer 13 corresponding to the outer peripheral side of the electrode group 4, and lithium is likely to precipitate.

Further, when the positive electrode 1 and the negative electrode 2 are wound in a spiral shape with the separator 3 interposed, a stronger tension than the outer peripheral side must be applied to the inner peripheral side of the electrode group 4. Therefore, on the inner peripheral side of the electrode group 4, the distance between the positive electrode 1 and the negative electrode 2 is shorter than the distance on the outer peripheral side of the electrode group 4. Accordingly, lithium is likely to be deposited also on the second end portion 13 b of the negative electrode mixture layer 13 corresponding to the inner peripheral side of the electrode group 4.

However, in the present embodiment, the thickness of both the first end portion 13a and the second end portion 13b of the negative electrode mixture layer 13 is made thinner than the thickness of the main portion of the mixture layer, and the surfaces of both ends are made lithium. It is covered with a surface layer 14 having high ion acceptability. Therefore, local precipitation of lithium can be suppressed.

(Second Embodiment)
FIG. 4 is a schematic diagram of a cross section of the negative electrode 2A in the present embodiment. Since the negative electrode 2A has substantially the same structure as the negative electrode 2 of the first embodiment except that the details of the end portions of the mixture layer and the surface layer are different, common constituent elements will be described using the same reference numerals.

The negative electrode 2A includes a strip-shaped rectangular negative electrode current collector 12 and a negative electrode mixture layer 13 formed on the surface thereof. Here, the first end portion 13a and the second end portion 13b are predetermined end portions having a thickness smaller than the main portion 13A of the mixture layer, and the thicknesses of the first end portion 13a and the second end portion 13b are as follows. It becomes thinner toward the extreme end of the end. The surfaces of the first end portion 13a and the second end portion 13b are covered with the surface layer 14 together with the surface of the main portion 13A. That is, the surface of the negative electrode mixture layer 13 is completely covered with the surface layer 14.

The thickness of the end corresponding portion of the surface layer 14 corresponding to the first end portion 13a and the second end portion 13b is on average larger than the thickness of the main portion corresponding portion. This makes it easy to control the balance between the lithium ion acceptability at the end of the mixture layer where lithium is likely to precipitate and the lithium ion acceptability at the main part.

Further, the thickness of the end corresponding portion of the surface layer 14 increases toward the end. Thereby, lithium ion acceptance property becomes large as it goes to the endmost part of a mixture layer. Note that the thickness of the end corresponding portion does not need to gradually increase in the entire region up to the end. For example, such a change may not be required in a region from the endmost part to 10 mm or 5 mm. Even in that case, it is possible to obtain a certain effect by gradually increasing the thickness of the end corresponding portion toward the end.

(Third embodiment)
FIG. 5 is a schematic view of a cross section of the negative electrode 2B in the present embodiment. The negative electrode 2B has substantially the same structure as that of the negative electrode 2 of the first embodiment except that the details of the end portions of the mixture layer and the surface layer are different. Therefore, common constituent elements will be described using the same reference numerals.

The negative electrode 2B includes a strip-shaped rectangular negative electrode current collector 12 and a negative electrode mixture layer 13 formed on the surface thereof. Also here, the first end portion 13a and the second end portion 13b are predetermined end portions having a thickness smaller than the main portion 13A of the mixture layer, and the thicknesses of the first end portion 13a and the second end portion 13b are as follows. It becomes smaller as it goes to the extreme end of the end. The surfaces of the first end portion 13a and the second end portion 13b are covered with the surface layer 14 together with the surface of the main portion 13A. That is, the surface of the negative electrode mixture layer 13 is completely covered with the surface layer 14.

The thickness of the portion corresponding to the end of the surface layer 14 increases as it goes toward the end, and also covers a part of the surface of the current collector 12. At this time, the distance from the extreme end of the mixture layer to the extreme end of the end corresponding portion of the surface layer 14 is, for example, 0.01 to 1 mm. Thereby, while being able to improve the lithium ion acceptability of the both ends of the negative mix layer 13, the surface layer 14 with high binding property with the collector 12 can be made to contact with the collector 12. FIG. Therefore, it is possible to effectively prevent the mixture layer from dropping off due to the expansion and contraction of the negative electrode 2B during charging and discharging. Thus, good charge / discharge cycle characteristics can be obtained.

(Fourth embodiment)
FIG. 6 is a schematic diagram of the front surface of the negative electrode 2C in the present embodiment. Since the negative electrode 2C has substantially the same structure as the negative electrode 2 of the first embodiment except that the coating layer and the surface layer have different application regions, the same reference numerals are used for common components.

The negative electrode 2C includes a strip-shaped rectangular negative electrode current collector 12 and a negative electrode mixture layer 13 formed on the surface thereof. However, the negative electrode mixture layer 13 is formed on the negative electrode current collector so that one end portion along the longitudinal direction of the current collector 12 is exposed. In the case of such a negative electrode, the thickness of the end portion along the longitudinal direction instead of the end portion along the short direction of the negative electrode current collector 12 can be a predetermined end portion having a small thickness. That is, the third end portion 13c and the fourth end portion 13d can be predetermined end portions having a thickness smaller than that of the main portion of the mixture layer.

Although not shown, in the negative electrode 2C, the thickness of the third end portion 13c and the fourth end portion 13d becomes smaller toward the extreme end of each end portion. And the surface of the 3rd end part 13c and the 4th end part 13d is covered with the surface layer 14 with the surface of the principal part.

In the negative electrode 2 </ b> C having the above-described configuration, a current collector plate serving as a current collector terminal is welded to the exposed portion of the current collector 12. Accordingly, electric charges are particularly concentrated on the exposed portion of the current collector 12, and lithium is likely to be deposited. Therefore, it is desirable that at least the third end portion 13c of the negative electrode mixture layer 13 be a predetermined end portion.

In the first to third embodiments, the thickness of both the first end and the second end of the negative electrode mixture layer 13 is made smaller than the thickness of the main part, and the end is covered with the surface layer. Although the case has been described, the thickness of only one of the first end portion and the second end portion may be made smaller than the thickness of the main portion, and the end portion may be covered with the surface layer. Moreover, in the said 4th Embodiment, the thickness of only one of a 3rd edge part and a 4th edge part may be made smaller than the thickness of a principal part, and the said edge part may be covered with a surface layer.

In the first to fourth embodiments, the case where the electrode group 4 in which the positive electrode 1 and the negative electrode 2 are wound in a spiral shape is described. However, the positive electrode 1 and the negative electrode 2 are stacked via the separator 3. The same effect can be obtained even when an electrode group is formed.

In the first to fourth embodiments, the case where the surface layer 14 is formed on the surface of the negative electrode mixture layer 13 has been described. However, the surface layer may be formed on the surface of the positive electrode mixture layer. Good. Furthermore, you may form a surface layer in the surface of both the positive mix layer and the negative mix layer, respectively.

(First reference form)
Next, a first reference embodiment of the present invention will be described with reference to FIG. FIG. 8 is a schematic diagram of a cross section of the electrode 2D in the present embodiment. Here, the same reference numerals are used for the components corresponding to those in the first embodiment.

The electrode 2D includes a strip-shaped rectangular current collector 12D and a mixture layer 13D formed on the surface thereof. Similarly to the negative electrode 2 of the first embodiment, the mixture layer 13 </ b> D includes a first end along the short direction of the current collector, a second end opposite to the first end, and the current collector 12. It is the rectangle which comprises the 3rd end part along the longitudinal direction, and the 4th end part on the opposite side of the 3rd end part. Portions other than the first to fourth end portions of the mixture layer 13 are main portions.

However, unlike the negative electrode 2 of the first embodiment, the thickness of the mixture layer at the first end and the second end of the electrode 2D is not particularly limited. The surfaces of the first end and the second end need not be covered with the surface layer 14. The surface layer 14 only needs to cover at least the main part of the mixture layer 13.

The maximum height roughness Rmax of the interface between the mixture layer 13 and the surface layer 14 is set to, for example, 3 to 25 μm, and further 5 to 20 μm. By setting the maximum height roughness Rmax in the above range, the anchor effect in adhesion between the mixture layer 13 and the surface layer 14 is increased, and the mixture layer 13 is suppressed from being exposed from the surface layer 14. Internal short circuit is extremely difficult to occur. In this case, by setting the thickness of the surface layer 14 to 3 to 20 μm, further 5 to 15 μm, the adhesion strength between the mixture layer 13 and the surface layer 14 can be further increased, and the battery capacity can be secured. It becomes easy.

The surface layer coating for forming the surface layer 14 may contain a second active material such as lithium titanium composite oxide, and may contain alumina, magnesia, silica, titania and the like. These ceramic powders may be used alone or in combination of two or more. Similar to the first embodiment, the surface layer coating is prepared by mixing the ceramic powder and optional binders, conductive materials, thickeners, and the like together with a dispersion medium using a disperser. .

The surface layer 13 may be formed on the surface of the negative electrode mixture layer, or may be formed on the surface of the positive electrode mixture layer. The surface layer paint may be applied immediately after the mixture paint is applied. In that case, the mixture layer coating and the surface layer coating are simultaneously dried and then rolled to form the mixture layer and the surface layer. Moreover, after drying the coating film of a mixture layer coating material and rolling and forming a mixture layer, you may apply | coat a surface layer coating material on the surface of a mixture layer. Moreover, after drying the coating film of the mixture layer coating, a process for forming irregularities on the coating film of the mixture layer coating for the purpose of adjusting the maximum height roughness Rmax of the interface between the mixture layer and the surface layer After that, the surface layer paint may be applied. However, the method for forming the mixture layer and the surface layer is not limited thereto.

(Second reference form)
Next, a second reference embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a schematic diagram of a cross section of the electrode 2E in the present embodiment. FIG. 10 is a partial schematic view of the surface of the electrode 2E. Here, the same reference numerals are used for the components corresponding to those in the first embodiment.

The electrode 2E includes a strip-shaped rectangular current collector 12E and a mixture layer 13E formed on the surface thereof. Similarly to the negative electrode 2 of the first embodiment, the mixture layer 13 </ b> E includes a first end along the short direction of the current collector, a second end opposite to the first end, and the current collector 12. It is the rectangle which comprises the 3rd end part along the longitudinal direction, and the 4th end part on the opposite side of the 3rd end part. Portions other than the first to fourth end portions of the mixture layer 13 are main portions.

However, unlike the negative electrode 2 of the first embodiment, the thickness of the mixture layer at the first end and the second end of the electrode 2E is not particularly limited. The surfaces of the first end and the second end need not be covered with the surface layer 14. The surface layer 14 only needs to cover at least the main part of the mixture layer 13. The surface layer 13 may be formed on the surface of the negative electrode mixture layer, or may be formed on the surface of the positive electrode mixture layer.

In the electrode 2E, a part of the mixture layer 13 is exposed, for example, in an island shape through the surface layer. Thereby, the impregnation property of the nonaqueous electrolyte to the mixture layer is not excessively hindered by the surface layer 14, and the impregnation property is improved.

As described above, examples of the method for partially exposing the mixture layer 13 include the following methods.

In the first method, the maximum height roughness Rmax of the interface between the mixture layer 13 and the surface layer 14 is set to be larger than 25 μm, for example, and preferably Rmax is set to 30 to 60 μm. Thereby, the unevenness | corrugation in the surface of the mixture layer 13 becomes large, and a part of convex part penetrates the surface layer 14. In this case, the surface layer paint may be applied immediately after the mixture paint is applied. In that case, the mixture layer coating and the surface layer coating are simultaneously dried and then rolled to form the mixture layer and the surface layer. Moreover, after drying the coating film of a mixture layer coating material and rolling and forming a mixture layer, you may apply | coat a surface layer coating material on the surface of a mixture layer.

In the second method, as shown in FIGS. 11 and 12, an outward projecting portion 15 is intentionally provided on the surface of the mixture layer 13. FIG. 11 is a schematic diagram of a cross section of the electrode 2F in a modification of the present embodiment. FIG. 12 is a partial schematic view of the surface of the electrode 2F. A part of the mixture layer 13 can be exposed by allowing the protruding portion 15 to penetrate the surface layer 14. The diameter of the protrusion is preferably 20 to 100 μm at the center height. When providing the protrusion 15 as described above, after the coating film of the mixture layer coating is dried, the coating film of the mixture layer coating is processed to form irregularities, and then the surface layer coating is applied. . As a process for forming irregularities on the coating film, for example, the coating film is rolled with a roller having concave portions in a regular pattern on the surface. Thereby, the mixture layer 13 which has the convex part 15 by a regular pattern can be obtained.

In the third method, as shown in FIGS. 13 and 14, a part of the mixture layer 13 is exposed by interspersing a plurality of through holes 16 in the surface layer 14. FIG. 13 is a schematic view of a cross section of an electrode 2G in another modification of the present embodiment. FIG. 14 is a partial schematic view of the surface of the electrode 2G. Such a through-hole 16 can be easily formed by enclosing a sufficient amount of bubbles in the surface layer paint. In this case, the diameter of the through hole is preferably 20 μm or less, for example. For example, lithium titanium composite oxide powder and optional components such as a binder and a conductive material are put into a dispersion medium and mixed by a dispersing machine such as a planetary mixer. At that time, for example, by using a rotating disk type disperser, a sufficient amount of air is included in the surface layer paint. As described above, when a surface layer coating material containing bubbles is applied to the surface of the mixture layer 13 and left for a while, the bubbles burst, and through holes are formed at positions corresponding to at least a part thereof.

The ratio of the area where the main part is exposed to the area of the main part of the mixture layer 13 (exposure degree) is preferably 60% or less, and more preferably 1 to 10%. By setting the exposure level within the above range, the speed at which the non-aqueous electrolyte is impregnated in the mixture layer can be sufficiently increased during the production of the battery while maintaining the high effect of suppressing the internal short circuit.
Next, based on an Example, this invention is demonstrated more concretely.

Example 1
In this example, a negative electrode having the same structure as that shown in FIG. 2 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using this negative electrode.

(Preparation of negative electrode)
<Mixture paint>
2.5 parts by mass of a dispersion of styrene-butadiene copolymer rubber particles (binder) (solid content 40% by weight) with respect to 100 parts by mass of artificial graphite (first active material) (1 mass in terms of solid content) Part), 1 part by mass of carboxymethylcellulose (CMC) (thickener) and an appropriate amount of water were mixed and stirred with a double-arm kneader to prepare a negative electrode mixture paint.

<Surface layer paint>
On the other hand, with respect to 100 parts by mass of lithium-titanium composite oxide (second active material, Li ₄ Ti ₅ O ₁₂ ), the same dispersion of styrene-butadiene copolymer rubber particles (solid content 40% by weight) as above was added. 5 parts by mass, 1 part by mass of CMC, 3.0 parts by mass of acetylene black (conductive material), and an appropriate amount of water were blended and stirred with a double-arm kneader to prepare a surface layer paint.

First, a negative electrode mixture paint is applied to both surfaces of a strip-like negative electrode current collector made of a copper foil having a thickness of 10 μm, and then dried. Next, a surface layer paint is applied to the surface of the coating film of the negative electrode mixture paint. It apply | coated so that it might become 20 mass parts with respect to 100 mass parts of mixture layers, and it dried. Then, it rolled so that the total thickness of a negative electrode collector and a coating film might be set to 200 micrometers, and the negative electrode was produced.

However, the thickness of both end portions (the first end portion and the second end portion) along the short direction of the negative electrode mixture layer was made thinner toward the respective end portions. Moreover, the surface layer was apply | coated to the whole surface of the mixture layer containing the surface of the both ends of a negative mix layer so that it might become uniform thickness, and the negative mix layer was completely covered with the surface layer.

The negative electrode lead was connected to the portion where the negative electrode current collector of the negative electrode was exposed, and then a protective tape was applied so as to cover the negative electrode lead.

(Preparation of positive electrode)
2 parts by mass of acetylene black (conductive material), 2 parts by mass of polyvinylidene fluoride (binder), and an appropriate amount of N-methyl-2-pyrrolidone per 100 parts by mass of lithium cobalt oxide (positive electrode active material) The mixture was stirred with a double arm kneader to prepare a positive electrode mixture paint. This paint was applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and rolled to a total thickness of 170 μm to obtain a positive electrode.

The positive electrode lead was connected to the portion where the positive electrode current collector of the positive electrode was exposed, and then a protective tape was applied so as to cover the positive electrode lead.

(Production of lithium ion secondary battery)
The positive electrode and the negative electrode were wound through a polyethylene microporous film (porous insulating layer) having a thickness of 20 μm to constitute an electrode group. The electrode group was inserted into the cylindrical battery case together with the insulating plate, and the negative electrode lead led out from the lower part of the electrode group was connected to the bottom of the battery case. Moreover, the positive electrode lead led out from the upper part of the electrode group was connected to the sealing plate. Thereafter, 5.5 g of a nonaqueous electrolyte was added, and then the opening of the battery case was sealed with a sealing plate to complete a lithium ion secondary battery. The nonaqueous electrolyte is obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent having a volume ratio of EC / 5DMC / MEC of 80/5/15. In the nonaqueous electrolyte, 3 parts by mass of VC was dissolved per 100 parts by mass of the mixed solvent.

Example 2
A surface layer is formed so that only the main part of the negative electrode mixture layer and the first end corresponding to the inner peripheral side of the electrode group are completely covered with the surface layer, and the second end corresponding to the outer peripheral side of the electrode group Was not covered with a surface layer, and a negative electrode was produced in the same manner as in Example 1. Further, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode was used.

Example 3
A surface layer is formed so that only the main part of the negative electrode mixture layer and the second end corresponding to the outer peripheral side of the electrode group are completely covered with the surface layer, and the first end corresponding to the inner peripheral side of the electrode group Was not covered with a surface layer, and a negative electrode was produced in the same manner as in Example 1. Further, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode was used.

Example 4
In this example, a negative electrode having the same structure as that shown in FIG. 4 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using this negative electrode. Specifically, after applying the same negative electrode mixture paint as in Example 1 to the current collector, the surface layer paint was applied to the surface of the paint film of the mixture paint without drying, and the two-layer paint film was formed. It was dried at the same time. Then, it rolled so that total thickness might be 200 micrometers, and produced the negative electrode. However, the thickness of the surface layer at both ends (first end and second end) is increased by increasing the pressure of the die coater that discharges the surface layer coating at the beginning and end of the coating of the surface layer coating. The size was gradually increased. The obtained negative electrode has basically the same structure as the negative electrode of Example 1, except that the structure of the surface layers at both ends is different. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

Example 5
In this example, a negative electrode having the same structure as that shown in FIG. 5 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using this negative electrode. Specifically, the negative electrode mixture layer and the surface layer were formed in substantially the same manner as in Example 1, using the same negative electrode mixture coating material and surface layer coating material as in Example 1. However, at the start and end portions of the coating film of the surface layer coating, the surface layer is formed in the vicinity of both ends (first end and second end) by shifting the discharge timing of the surface layer coating from the die coater. Are provided as a single layer on the surface of the negative electrode current collector. The obtained negative electrode has basically the same structure as the negative electrode of Example 1, except that the structure of the surface layers at both ends is different. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 1)
In this example, a negative electrode 2H having a structure as shown in FIG. 7 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using the negative electrode 2H. Specifically, the negative electrode mixture layer 13 and the surface layer 14 were formed in substantially the same manner as in Example 1, using the same negative electrode mixture coating material and surface layer coating material as in Example 1. However, at the start and end portions of the coating film of the surface layer paint, both ends (the first end portion 13a and the second end portion 13b) are placed on the surface layer 14 by shifting the discharge timing of the surface layer paint from the die coater. It was not covered with and exposed. The obtained negative electrode has basically the same structure as the negative electrode of Example 1, except that the structure of the surface layers at both ends is different. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

[Evaluation]
For the lithium ion secondary batteries of Examples 1 to 5 and Comparative Example 1, the charge / discharge cycle characteristics were evaluated in the following manner. The evaluation results are shown in Table 1.

(I) First, the battery after completion was conditioned and discharged twice, and then stored in a 45 ° C. environment for 7 days.
(Ii) Next, the following charge / discharge cycle was repeated 500 times.
Charging: Charging was performed at a constant current of 1400 mA up to a charging end voltage of 4.2 V, and then, constant voltage charging was performed at 4.2 V until the charging current decreased to 100 mA.
Discharge: Discharged to a final discharge voltage of 3 V at a constant current of 2000 mA.
A combination of the above charging and discharging is defined as one cycle.
(Iii) The ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle was determined as the capacity retention rate after 500 cycles.
(Iv) Next, the battery after the charge / discharge cycle was repeated 500 times was disassembled, and the lithium deposition state inside the electrode group was observed.

As shown in Table 1, when the end portion of the negative electrode mixture layer was covered with a surface layer, lithium deposition at the end portion of the mixture layer was suppressed, and the capacity retention rate after 500 cycles was also It is high. Further, as in Examples 2 and 3, even when only one end portion along the short direction of the negative electrode mixture layer is covered with the surface layer, an effect of improving the capacity retention rate is seen as compared with Comparative Example 1. . Moreover, it turns out that the capacity | capacitance maintenance factor becomes higher in the direction which covers the edge part of an outer peripheral side with a surface layer rather than the inner peripheral side of an electrode group. This is presumably because the position of the negative electrode lead is located near the outer peripheral end of the negative electrode current collector. That is, it is presumed that the effect of suppressing lithium deposition is greater when the end portion of the mixture layer located in the vicinity of the current collecting portion where lithium is likely to precipitate is covered with the surface layer.

Further, in Example 4 in which the thickness of the surface layer of the end corresponding portion of the negative electrode mixture layer was gradually increased, lithium deposition was suppressed in the same manner as in Example 1, and the capacity retention rate after 500 cycles was Better than 1. From this, it is presumed that the action of the surface layer becomes obvious by gradually increasing the thickness of the surface layer toward the extreme end.

Furthermore, in Example 5 in which the surface layer was bound from the end of the negative electrode mixture layer to the surface of the negative electrode current collector, lithium deposition was suppressed in the same manner as in Example 1, and the capacity was maintained after 500 cycles. The rate was further improved than in Example 1. This is presumably because the binding force between the surface layer and the negative electrode current collector was increased, and the mixture was prevented from falling off at the end of the negative electrode mixture layer.

On the other hand, in Comparative Example 1 in which both ends of the negative electrode mixture layer are not covered with the surface layer, lithium is deposited at both the inner and outer ends, and the capacity retention rate after 500 cycles is also obtained. It was low.

As described above, by covering the end portion of the negative electrode mixture layer with the surface layer, precipitation of lithium at the end portion of the negative electrode mixture layer can be suppressed, and furthermore, the surface layer having a high binding force and the negative electrode current collector By contacting, it was possible to prevent the mixture from falling off at the end of the negative electrode mixture layer, and it was confirmed that it was advantageous for improving the capacity retention rate.

In Examples 1 to 5, the surface layer was provided in the negative electrode mixture layer to improve the reactivity with lithium, but the surface layer was provided in the positive electrode mixture layer to improve the reactivity with lithium. A similar effect can also be obtained by improving.

<< Reference Example 1 >>
(Preparation of negative electrode)
In this reference example, a negative electrode having the same cross-sectional structure as shown in FIG. 8 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using this negative electrode. Specifically, the negative electrode mixture paint and the surface layer paint similar to those in Example 1 were used, and the negative electrode mixture layer and the surface layer were formed in substantially the same manner as in Comparative Example 1 except for the following points. Got.

In this reference example, the viscosity ratio between the surface layer coating material and the mixture coating material was adjusted to be 1: 0.01 to 0.05. Moreover, after apply | coating the above-mentioned mixture coating material, the surface layer coating material was apply | coated to the surface of the coating film of mixture coating material, without making it dry, and the two-layer coating film was dried simultaneously. Thereafter, the coating film and the current collector are rolled, and the thickness of the negative electrode mixture layer per side is 84 μm, the thickness of the surface layer 13 is 10 μm, and the maximum height roughness of the interface between the negative electrode mixture layer and the surface layer A negative electrode having an Rmax of 3 μm was produced.

In the obtained negative electrode, the negative electrode mixture layer was not exposed from the surface layer, and the surface layer completely covered the mixture layer as shown in FIG.

(Preparation of positive electrode)
Mixing 1 part by weight of acetylene black (conductive material), 1 part by weight of polyvinylidene fluoride (binder), and an appropriate amount of NMP with respect to 100 parts by weight of lithium cobalt oxide (positive electrode active material) The mixture was stirred with a combination machine to prepare a positive electrode mixture paint. This paint was applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm, dried, and rolled so that the thickness of the mixture layer per side was 74 μm, thereby obtaining a positive electrode.

(Production of lithium ion secondary battery)
A battery similar to that shown in FIG. 1 was produced in the same manner as in Example 1 except that the above-described negative electrode and positive electrode produced in this reference example were used.

(Reference Example 2)
A negative electrode was produced in the same manner as in Reference Example 1 except that the viscosity ratio of the surface layer coating material to the mixture coating material was adjusted to be 1: 0.2 to 1.0. In the obtained negative electrode, the negative electrode mixture layer was not exposed from the surface layer, and the surface layer completely covered the mixture layer as shown in FIG. The thickness of the negative electrode mixture layer per side was 84 μm, the thickness of the surface layer 13 was 10 μm, and the maximum height roughness Rmax of the interface between the negative electrode mixture layer and the surface layer was 25 μm. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

(Reference Example 3)
The viscosity ratio between the surface layer paint and the mixture paint is adjusted to be 1: 0.05 to 0.2, the negative electrode mixture layer thickness per side is 91 μm, the surface layer thickness is 3 μm, and the negative electrode mixture A negative electrode was produced in the same manner as in Reference Example 1 except that the maximum height roughness Rmax at the interface between the agent layer and the surface layer was 15 μm. In the obtained negative electrode, the negative electrode mixture layer was not exposed from the surface layer, and the surface layer completely covered the mixture layer as shown in FIG. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

(Reference Example 4)
A negative electrode was produced in the same manner as in Reference Example 3 except that the thickness of the negative electrode mixture layer per side was 74 μm and the thickness of the surface layer was 20 μm. In the obtained negative electrode, the negative electrode mixture layer was not exposed from the surface layer, and the surface layer completely covered the mixture layer as shown in FIG. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

(Reference Example 5)
A negative electrode was produced in the same manner as in Reference Example 2 except that the thickness of the negative electrode mixture layer per side was 91 μm and the thickness of the surface layer was 3 μm. In the obtained negative electrode, the negative electrode mixture layer was not exposed from the surface layer, and the surface layer completely covered the mixture layer as shown in FIG. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the obtained negative electrode was used.

For the batteries of Reference Examples 1 to 5, the thickness of the negative electrode mixture layer, the thickness of the surface layer, the maximum height roughness Rmax of the interface between the negative electrode mixture layer and the surface layer, the presence or absence of exposure of the negative electrode mixture layer, and the internal The evaluation results of the short circuit test are shown in Table 2.

[Evaluation]
<Presence or absence of exposure of mixture layer>
The surface and cross section of the negative electrode were observed with an electron microscope, and it was confirmed whether or not the active material of the negative electrode mixture layer was exposed from the surface layer.

<Maximum roughness Rmax>
The cross section of the negative electrode was observed with an electron microscope, and the distance in the thickness direction between the interface farthest from the current collector and the interface closest to the current collector among the interface between the mixture layer and the surface layer was measured.

<Internal short circuit test>
For each reference example, 5 cells of each battery were prepared. And after charging each battery, the electrode group was taken out from the battery case. Next, a metal piece having an arbitrary size was interposed between the positive electrode located on the outermost periphery of the electrode group and the separator. And the electrode group which interposed the metal piece was again accommodated in the battery case. Next, the side surface of the battery was pressed with a predetermined pressure. And in each reference example, the number of cells short-circuited among the five cells (number of short-circuited cells / 5) was confirmed.

As is clear from Table 2, in Reference Examples 1 to 5, since there is no defect in the internal short circuit test, it is considered that the safety and charge / discharge cycle characteristics are excellent. From the above, it can be seen that the thickness of the surface layer is preferably 3 to 20 μm, and the maximum height roughness of the interface is preferably 3 to 25 μm.

In Reference Examples 1 to 5, the surface layer was formed on the surface of the negative electrode mixture layer, but the surface layer may be formed on the surface of the positive electrode mixture layer, and in that case, a similar effect can be obtained. .

<< Reference Example 6 >>
(Preparation of negative electrode)
In this reference example, a negative electrode having a structure as shown in FIGS. 9 and 10 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using the negative electrode. Specifically, the negative electrode mixture paint and the surface layer paint similar to those in Example 1 were used, and the negative electrode mixture layer and the surface layer were formed in substantially the same manner as in Comparative Example 1 except for the following points. Got. That is, in this reference example, a part of the mixture layer was exposed from the surface layer.

In this reference example, the surface roughness of the mixture layer was increased by increasing the flow rate when the surface layer coating was applied to the coating film of the mixture coating before drying. Then, a negative electrode having a total thickness of the negative electrode mixture layer and the surface layer per side of 94 μm and a maximum height roughness Rmax of 30 μm at the interface between the negative electrode mixture layer and the surface layer was prepared. When the surface layer of the obtained negative electrode was observed, a part of the negative electrode mixture layer was exposed from the surface layer. The degree of exposure was 10%. When the distribution of exposure per square centimeter of the area where the surface layer was applied (main part of the mixture layer) was taken, there was a variation of 0.01 to 20%. Next, a lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that the obtained negative electrode was used.

<< Reference Example 7 >>
In this reference example, a negative electrode having a structure as shown in FIGS. 11 and 12 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using the negative electrode. Specifically, the negative electrode mixture paint and the surface layer paint similar to those in Example 1 were used, and the negative electrode mixture layer and the surface layer were formed in substantially the same manner as in Comparative Example 1 except for the following points. Got.

In this reference example, after forming the negative electrode mixture layer, a protrusion was provided on the mixture layer, and then a surface layer coating was applied to form a surface layer. Specifically, the negative electrode mixture paint was applied to the surface of the current collector, the coating film was dried, and then the coating film was rolled with a roller in which elliptical hemispherical recesses having a depth of 10 μm were formed at intervals of 500 μm. . Thus, a negative electrode mixture layer having an elliptical hemispherical protrusion having a height of 10 μm was formed. Thereafter, a surface layer coating was applied to the surface of the negative electrode mixture layer and dried. Thereafter, the coating film was rolled with a roller having no recess as described above, and a negative electrode having a total thickness of 94 μm of the negative electrode mixture layer and the surface layer per side was produced. When the surface layer of the obtained negative electrode was observed, a part of the negative electrode mixture layer was exposed from the surface layer. The degree of exposure was 0.1%. Next, a lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that the obtained negative electrode was used.

<< Reference Example 8 >>
A negative electrode was produced in the same manner as in Reference Example 7 except that a roller in which elliptical hemispherical recesses having a depth of 10 μm were formed at intervals of 27 μm was used as a roller for rolling the coating film of the negative electrode mixture paint. When the surface layer of the obtained negative electrode was observed, a part of the negative electrode mixture layer was exposed from the surface layer. The degree of exposure was 60%. Next, a lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that the obtained negative electrode was used.

<< Reference Example 9 >>
In this reference example, a negative electrode having a structure as shown in FIGS. 13 and 14 was produced, and a non-aqueous secondary battery similar to that shown in FIG. 1 was produced using the negative electrode. Specifically, the negative electrode mixture paint and the surface layer paint similar to those in Example 1 were used, and the negative electrode mixture layer and the surface layer were formed in substantially the same manner as in Comparative Example 1 except for the following points. Got.

In this reference example, a sufficient amount of bubbles were included in the surface layer coating material, and the bubbles were ruptured, thereby interspersing a plurality of through holes in the surface layer. Specifically, in the preparation of the surface layer coating material, the air was encapsulated in the coating material with a rotating disk type disperser after stirring with a double-arm kneader.

The negative electrode mixture paint was applied to the current collector, dried, and after rolling, the surface layer paint was applied to the surface of the negative electrode mixture layer. Then, the coating film of the surface layer coating material was dried. At that time, bubbles contained in the surface layer coating burst during drying, and a large number of minute through holes having a diameter of about 20 μm or less were formed. The thickness of the negative electrode mixture layer per side was 84 μm, and the thickness of the surface layer was 10 μm. The degree of exposure of the negative electrode mixture layer from the surface layer was 1%.

<< Reference Example 10 >>
In this reference example, the surface roughness of the mixture layer was reduced. And the negative electrode mixture layer thickness per one side was 79 micrometers, the thickness of the surface layer was 15 micrometers, and the negative electrode whose maximum height roughness Rmax of the interface of a negative electrode mixture layer and a surface layer was 20 micrometers was produced. When the surface layer of the obtained negative electrode was observed, the negative electrode mixture layer was not exposed from the surface layer (exposure degree 0%). Next, a lithium ion secondary battery was produced in the same manner as in Reference Example 1 except that the obtained negative electrode was used.

Table 3 shows the results of evaluation of the degree of exposure of the negative electrode mixture layer, the non-aqueous electrolyte injection property, and the charge / discharge cycle characteristics of the batteries of Reference Examples 6 to 10.

[Evaluation]
<Exposure>
The surface and cross section of the negative electrode were observed with an electron microscope and determined by surface image processing.

<Injectability of non-aqueous electrolyte>
When the batteries of Reference Examples 6 to 10 were manufactured, the time required to impregnate the electrode group with 5.5 g of nonaqueous electrolyte was measured.

<Charge / discharge cycle characteristics>
This is the same as the evaluation method in Examples 1 to 5.

As is clear from Table 3, in Reference Examples 6 to 9 where the negative electrode mixture layer was exposed from the surface layer, the injection time was much longer than in Reference Example 10 where the negative electrode mixture layer was not exposed from the surface layer. It has become shorter. This indicates that in Reference Example 10, impregnation of the nonaqueous electrolyte into the negative electrode mixture layer is hindered by the surface layer covering the negative electrode mixture layer. In Reference Examples 6 to 9, since the nonaqueous electrolyte is impregnated from the exposed portion of the negative electrode mixture layer, the nonaqueous electrolyte is uniformly impregnated over the entire negative electrode, and it is assumed that the injection time is shortened. Further, when the degree of exposure of the negative electrode mixture layer from the surface layer was in the range of 0.1 to 60%, the capacity retention rate was also good.

From the above, it can be seen that by exposing a part of the negative electrode mixture layer from the surface layer, it is advantageous to achieve both good liquid injection properties and excellent charge / discharge cycle characteristics.

The electrode plate for a non-aqueous secondary battery according to the present invention is excellent in charge / discharge cycle characteristics, and thus is useful as a power source for various electronic devices, communication devices, and mobile objects that are desired to have a long life. For example, it is useful as a power source for a multifunctional portable device or a power source for an EV (electric vehicle) or HEV (hybrid vehicle).

Although the present invention has been described in terms of the presently preferred embodiments, such disclosure should not be construed as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains after reading the above disclosure. Accordingly, the appended claims should be construed to include all variations and modifications without departing from the true spirit and scope of this invention.

1: positive electrode, 2: negative electrode, 3: porous insulating layer, 4 electrode group, 5: battery case, 6: insulating plate, 7: negative electrode lead, 8: positive electrode lead, 9: sealing plate, 10: gasket, 11: Lithium ion secondary battery, 12: negative electrode current collector, 13: negative electrode mixture layer, 14: surface layer, 15: protrusion

Claims

A rectangular current collector, and a mixture layer containing a first active material formed on the surface of the current collector,
The mixture layer includes a first end along one end of the current collector, a second end opposite to the first end, and the other end perpendicular to the one end of the current collector. A third end along the fourth end, a fourth end opposite to the third end, and a main part other than the first to fourth ends,
The thickness of at least one predetermined end selected from the group consisting of the first to fourth ends is smaller than the thickness of the main part of the mixture layer,
The electrode plate for a non-aqueous secondary battery, wherein the surface of the predetermined end is covered with a surface layer containing a second active material that is more reactive with lithium than the first active material.
The electrode plate for a non-aqueous secondary battery according to claim 1, wherein a thickness of the predetermined end portion becomes smaller toward an endmost portion of the predetermined end portion.
The surface layer has an end corresponding portion that covers the surface of the predetermined end portion, and a main portion corresponding portion that covers the surface of the main portion of the mixture layer,
The electrode plate for a non-aqueous secondary battery according to claim 1 or 2, wherein a thickness of the end corresponding part is larger than a thickness of the main part corresponding part.
The electrode plate for a non-aqueous secondary battery according to claim 3, wherein a thickness of the end corresponding portion increases toward the endmost portion of the predetermined end.
The electrode plate for a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the surface layer covers a surface of the predetermined end portion and covers at least a part of a surface of the current collector. .
The non-height according to any one of claims 3 to 5, wherein the maximum height roughness Rmax at the interface between the main part of the mixture layer and the main part corresponding part of the surface layer is 3 to 25 µm. Electrode plate for aqueous secondary battery.
The electrode plate for a non-aqueous secondary battery according to claim 6, wherein the thickness of the main part corresponding part is 3 to 20 µm.
The electrode plate for a non-aqueous secondary battery according to any one of claims 3 to 7, wherein a part of a main part of the mixture layer is exposed from a main part corresponding part of the surface layer.
The non-aqueous secondary battery according to claim 8, wherein the main part corresponding part is dotted with a plurality of through holes, and a part of the main part of the mixture layer is exposed from the through holes. Electrode plate.
The electrode plate for a non-aqueous secondary battery according to claim 8 or 9, wherein a ratio of an area where the main part is exposed to an area of the main part is 60% or less.
The first active material is a carbon material capable of reversibly occluding and releasing lithium ions;
The electrode plate for a non-aqueous secondary battery according to any one of claims 1 to 10, wherein the second active material is a lithium titanium composite oxide capable of reversibly occluding and releasing lithium ions.
An electrode group, a non-aqueous electrolyte, and an exterior body that houses the electrode group together with the non-aqueous electrolyte,
The electrode group includes a positive electrode, a negative electrode, and a porous insulating layer interposed between the positive electrode and the negative electrode,
The positive electrode and the negative electrode are laminated or wound through the porous insulating layer,
A nonaqueous secondary battery, wherein at least one of the positive electrode and the negative electrode is the electrode plate for a nonaqueous secondary battery according to any one of claims 1 to 10.