Patent Publication Number: US-2011052954-A1

Title: Battery, method of manufacturing the same and non-aqueous secondary battery using the same

Description:
TECHNICAL FIELD 
     The present invention relates to an electrode plate used in a nonaqueous secondary battery typified by a lithium-ion cell and to a nonaqueous secondary battery using the same. 
     BACKGROUND ART 
     In recent years, lithium secondary batteries having been widely used as power supplies for portable electronic devices have a negative electrode made of a carbonic material or the like capable of occluding and releasing lithium, and a positive electrode made of an active material of a composite oxide containing a transition metal and lithium, e.g., LiCoO 2 . A secondary battery with a high voltage and a high discharge capacity has thus been realized. 
     With the multi-functionalization of electronic and communication devices in recent years, there has been demand for further increasing the capacity of lithium secondary batteries. 
     As a measure taken to increase the capacity, forming of an electrode plate containing a larger amount of active material and having a uniform thickness has been discussed. 
     As a way to uniformize an electrode plate in thickness, a roll method and an application method are mainly used. 
     In a roll method described in, for example, Patent Literature 1, as shown in  FIG. 14 , a positive electrode composite material  101  in a wet state is supplied between heating rolls  100   a  and  100   b  and between heating rolls  100   c  and  100   d . When the positive electrode composite material  101  in a wet state is formed into a sheet form, the heating rolls  100   a  to  100   d  heat the positive electrode composite material  101  to reduce the water content therein. 
     A sheet  102   a  formed by the heating rollers  100   a  and  100   b  passes through between the heating roll  100   b  and a pressure-bonding roll  103   a  and is supplied onto one of two surfaces of a current collector plate  104 . 
     A sheet  102   b  formed by the heating rollers  100   c  and  100   d  passes through between the heating roll  100   d  and a pressure-bonding roll  103   b  and is supplied onto the other of the surfaces of the current collector plate  104 . The sheets  102   a  and  102   b  supplied onto the two surfaces of the current collector plate  104  interposed between the sheets  102   a  and  102   b  pass through between the pressure-bonding rolls  103   a  and  103   b  and active material layers  105  are pressure-bonded to the two surfaces of the current collector plate  104 . 
     In an application method described, for example, in Patent Literature 2, a coating material in liquid form having a viscosity lower than that in the roll method is applied on a current collector plate and dried to form an active material layer  105 . Specifically, in the case of application on the surface of a current collector plate  104  in strip form as shown in  FIG. 15 , a surface tension occurs on a composite coating material, so that an end portion  1   a  of a composite material layer  1  slopes gently (a slope in the thickness direction of about X/Z=10) and a portion A protrudes at a corner portion. This shape is maintained even after drying, resulting in nonuniformity in thickness. 
     Then, the current collector plate  104  on which the active material layer  105  is laminated is cut with a slitter (not shown) along cutting lines  106   a  and  106   b  where the portion A can be removed, in the longitudinal direction of the current collector plate  104 . 
     Because an exposed surface (a plain portion described below) of the current collector plate  104  and a corner portion in the longitudinal direction of the active material layer  105  laminated on the current collector plate  104  are cut and removed with a slitter as described above, the plain portion where the surface of the current collector plate  104  is exposed is formed at or in the vicinity of the end portion of an electrode plate in the longitudinal direction in order to form a battery by connecting the current collector plate  104  of the electrode plate to a sealing plate functioning as positive output or to a battery case functioning as a negative electrode. Specifically, a masking tape  107   a  is applied on the current collector plate  104 , as shown in  FIG. 16(   a ), and the active material layer  105  is coated thereon. 
     As shown in  FIG. 16(   b ), a masking tape  107   b  is also applied on the other surface of the current collector plate  104  and another active material layer  105  is coated thereon. 
     Referring to  FIG. 16(   c ), rolling is performed with a roll press. 
     Thereafter, as shown in  FIG. 16(   d ), the masking tapes  107   a  and  107   b  are separated to form plain portions  108   a  and  108   b  so as to have a uniform thickness even in an end portion. 
     CITATION LIST 
     Patent Literatures 
     Patent Literature 1: Japanese Patent No. 2869156 
     Patent Literature 2: Japanese Patent Laid-Open No. 2005-183181 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the case of the roll method according to Patent Literature 1, however, it is difficult to dry the positive electrode composite material  101  on the heating rolls  100   a  to  100   d  between which the positive electrode composite material passes through in several minutes, for application to a nonaqueous secondary battery such as a lithium-ion cell made by mainly using a solvent such as N-methyl-2-pyrrolidone having a high boiling point and high wettability. The positive electrode composite material  101  is therefore pressure-bonded to the current collector plate  104  while being in a wet state to cause breaks in the active material layers  105  laminated on the current collector plate  104  or partial attachment of the active material layers  105  on the current collector plate  104 , thereby causing a nonuniformity in film thickness. Thus, the charge/discharge capacity of the nonaqueous secondary battery is reduced. 
     On the other hand, the application method according to Patent Literature 2 has a problem that the active material layers  105  are separated around the boundaries between the active material layers  105  on the masking tapes  107   a  and  107   b  and the active material layers  105  firmly bonded by a binder to active material layers  203  on the electrode plate, when the masking tapes  107   a  and  107   b  are separated. In a case where a nonaqueous secondary battery is formed by using the thus-formed electrode plate as a positive electrode plate or a negative electrode plate and by immersing in an electrolytic solution the positive and negative electrode plates opposed to each other with a separator interposed therebetween, there is a risk that a separated or almost separated chip of the active material layer  105  breaks through the separator to cause an internal short circuit. 
     Further, if a fluorinated resin having high repellency to a liquid is used in order to secure the releasability of the masking tapes  107   a  and  107   b , there is a risk of including air bubbles in the active material layers  105  due to the repellency. Consequently, the active material layers  105  having gaps formed therein after drying are depressed by pressing to have nonuniform films. 
     An object of the present invention is to provide an electrode plate that can hold a larger amount of an active material and have a uniform composite material layer in thickness. 
     Solution to Problem 
     A nonaqueous secondary battery electrode plate according to the present invention is a nonaqueous secondary battery electrode plate in a nonaqueous secondary battery including a positive electrode plate having a composite lithium oxide as an active material, and a negative electrode plate having as an active material a material capable of retaining lithium, the positive electrode plate and the negative electrode plate being opposed to each other with a separator interposed therebetween and being immersed in an electrolytic solution containing a nonaqueous solvent. The positive electrode plate or the negative electrode plate is formed by laminating the composite material layer of the active material on a surface of a current collector plate. A slope in a thickness direction (X/Z) of the end surfaces of the composite material layer along the longer sides of the current collector plate is “0&lt;(X/Z)≦1”. Preferably, the slope in the thickness direction (X/Z) of the end surfaces of the composite material layer along the longer sides of the current collector plate is “0.2≦(X/Z)≦1”. 
     The positive electrode plate is formed by laminating on the current collector plate a positive electrode composite coating material prepared by kneading and dispersing in a nonaqueous dispersion medium an active material including at least a lithium-containing composite oxide, an electroconductive material and a non-water-soluble high polymer binder. The proportion by volume of the active material, the binder and the electroconductive material is such that the binder is “10” or less and the electroconductive material is “10” or less with respect to “100” of the active material. 
     The negative electrode plate is formed by laminating on the current collector plate a negative electrode composite coating material prepared by kneading and dispersing in a dispersion medium an active material including at least a material capable of retaining lithium, and a water-soluble high polymer binder. 
     The positive electrode plate or the negative electrode plate has the composite material layer laminated on the current collector plate so that plain portions where a surface of the current collector plate is exposed from the ends along the longer sides of the current collector plate are left. 
     The positive electrode plate or the negative electrode plate has the composite material layer laminated from the ends along the longer sides of the current collector plate. 
     A nonaqueous secondary battery according to the present invention is formed by enclosing an electrode group and a nonaqueous electrolytic solution in a battery case, the electrode group being formed by winding or laminating the above-described nonaqueous secondary battery electrode plate, and an electrode plate opposed to the nonaqueous secondary battery electrode plate with a separator interposed between the electrode plates. 
     A method of manufacturing a nonaqueous secondary battery electrode plate according to the present invention includes, to form a composite material layer on a current collector plate, a first step of forming a composite material layer film by continuously extruding, from a die onto a first roll, a wet composite material in the form of a clay obtained by mixing an active material, a solvent and a binder soluble in the solvent or mixing an active material, a solvent, a binder soluble in the solvent and an electroconductive material; a second step of stretching the composite material layer film to have a constant width, while rolling the composite material layer film to have a constant thickness by a second roll opposed to the first roll on which the composite material layer film is put, and shaping, with regulator plates set on the second roll, a slope in a thickness direction (X/Z) of the end surfaces along the longer sides of the current collector plate; and a third step of pressure-bonding the composite material layer film shaped in the second step to the current collector plate by a third roll opposed to the second roll, and drying the composite material layer film to form the composite material layer on the current collector electrode. The thickness of the composite material layer film is shaped at such a compression ratio that when the film thickness of the composite material layer film after the first step is “1”, the film thickness after the second step is “not smaller than 0.4 and not larger than 0.6”, and the film thickness after the third step is “not larger than 0.2”. 
     When surface roughness Ra of the first and second rolls and the current collector plate is the surface roughness of the first roll: a 1 , the surface roughness of the second roll: a 2 , and the surface roughness of the current collector plate: a 3 , “a 1 &gt;a 2 &gt;a 3 ”. 
     The mixing of the active material, the solvent and the binder soluble in the solvent or the mixing of the active material, the solvent, the binder soluble in the solvent and the electroconductive material is performed in kneading by a kneading extruder. 
     The composite material layer with a constant width in the longitudinal direction may be removed before the drying in the third step to form a plain portion. 
     ADVANTAGEOUS EFFECTS OF INVENTION 
     In the nonaqueous secondary battery electrode plate thus constructed, the composite material layer of the active material is laminated on the surface of the current collector plate so that the slope in the thickness direction (X/Z) of the end surfaces of the composite material layer along the longer sides of the current collector plate is “0&lt;(X/Z)≦1”. Thus an electrode plate having a uniform thickness and a nonaqueous secondary battery having high capacity can be realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an essential portion of an apparatus for manufacturing a nonaqueous secondary battery electrode plate in Embodiment 1 of the present invention; 
         FIG. 2  is an enlarged sectional view of the essential portion shown in  FIG. 1 ; 
         FIG. 3  is an enlarged perspective view of the electrode plate in Embodiment 1; 
         FIG. 4  is a partially cutaway perspective view of a cylindrical secondary battery; 
         FIG. 5  is a diagram schematically showing a die in Embodiment 1; 
         FIG. 6  is a sectional view taken along a direction perpendicular to the lengthwise direction of the electrode plate in Embodiment 1; 
         FIG. 7  is a sectional view taken along a direction perpendicular to the lengthwise direction of an electrode plate in a comparative example; 
         FIG. 8  is a partially cutaway perspective view of a nonaqueous secondary battery in Embodiment 2 of the present invention; 
         FIG. 9  is an enlarged perspective view of an electrode plate in Embodiment 2; 
         FIG. 10  is a partially cutaway perspective view of a nonaqueous secondary battery in Embodiment 3 of the present invention; 
         FIG. 11  is an enlarged perspective view of an electrode plate in Embodiment 3; 
         FIG. 12  is an enlarged perspective view of an essential portion of an apparatus for manufacturing the electrode plate in Embodiment 3; 
         FIG. 13  is a perspective view of an essential portion of an apparatus for manufacturing a nonaqueous secondary battery electrode plate in Embodiment 4 of the present invention; 
         FIG. 14  is a diagram showing the configuration of an apparatus for manufacturing an electrode plate in the conventional art; 
         FIG. 15  is an enlarged perspective view of the electrode plate in the conventional art; 
         FIG. 16  is a diagram for explaining the method of manufacturing the electrode plate in the conventional art; 
         FIG. 17  shows a sectional view of the electrode plate in Embodiment 1 and a plan view of the electrode plate disassembled from a battery configured by using the electrode plate; and 
         FIG. 18  is a diagram showing the results of an experiment on the electrode plate area ratio A/(A+B) of a portion impregnated with an electrolytic solution with respect to a slope (X/Z) of a composite material layer. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to  FIGS. 1 to 13 ,  17 , and  18 . 
     Embodiment 1 
       FIGS. 1 to 6  show Embodiment 1 of the present invention. 
       FIG. 4  shows a nonaqueous secondary battery using a nonaqueous secondary battery electrode plate according to the present invention. The nonaqueous secondary battery is assembled by a procedure described below. 
     First, an electrode group  14  is made by winding in spiral form a positive electrode plate  6  having a composite lithium oxide as an active material and a negative electrode plate  7  having as an active material a material capable of retaining lithium, with a separator  8  interposed between the positive electrode plate  6  and the negative electrode plate  7 . 
     Next, the electrode group  14  is housed in a battery case  11  in the form of a cylindrical tube closed at its bottom. Thus, a negative electrode current collector plate  10  connected to the lower portion of the electrode group  14  is connected to the bottom portion of the battery case  11  by a negative electrode lead  16 . 
     Next, a positive electrode current collector plate  9  connected to the upper portion of the electrode group  14  is connected to a sealing plate  12  by a positive electrode lead  15 . 
     An electrolytic solution (not shown) composed of a predetermined quantity of a nonaqueous solvent is injected into the battery case  11 . The sealing plate  12  having a sealing gasket  13  attached to the peripheral end portion thereof is thereafter inserted in an opening portion of the battery case  11 , and the opening portion of the battery case  11  is inwardly bent for caulk sealing. 
     In the above-described electrolytic solution, various lithium compounds such as LiPF6 and LiBF4 may be used as an electrolytic salt. As the solvent, one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and methylethyl carbonate (MEC) or a combination of these compounds may be used. Further, it is preferable to use vinylene carbonate (VC), cyclohexyl benzene or a compound obtained by modifying them in order to form a good film on the positive electrode plate  6  or the negative electrode plate  7  and ensure stability in the event of overcharge. 
     The separator  8  is not particularly specified as long as it has such a composition as to endure within the range of use of the lithium-ion secondary battery. 
     However, a microporous film of an olefin resin such as polyethylene or polypropylene is ordinarily used singly or in composite form for the separator  8 , and is a preferable form. The thickness of the separator  8 , not particularly specified, may be set to 10 to 25 μm. 
     The positive electrode plate  6  and the negative electrode plate  7  are identical in structure to each other and are made by the same method, while only the active materials therein are different from each other. Only the method of manufacturing the positive electrode plate  6  will therefore be described. 
     For a current collector plate  2  for the positive electrode plate  6 , a metal foil having a thickness of 5 μm to 30 μm and formed of aluminum, an aluminum alloy, nickel, or a nickel alloy is used. As a composite material applied on the current collector plate  2 , a wet composite material is made in the form of clay with a viscosity of 1000 Pa·s or more by mixing, dispersing and kneading a positive electrode active material, an electroconductive material and a binder or an electroconductive material by a disperser such as a planetary mixer or an extruder so that they are uniformly dispersed in a dispersion medium. 
     Examples of the positive electrode active material include composite oxides such as a lithium cobalt oxide, a compound obtained by modifying the same (e.g., a compound obtained by solid-solving aluminum or magnesium in a lithium cobalt oxide), a lithium nickel oxide, a compound obtained by modifying the same (e.g., a compound obtained by replacing part of nickel with cobalt), a lithium manganese oxide and a compound obtained by modifying the same. 
     As the electroconductive material at this time, one of carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black, and various graphites or a combination of these may be used. 
     As the binder for the positive electrode at this time, polyvinylidene fluoride (PVdF), a compound obtained by modifying the same, polytetrafluoroethylene (PTFE) or a thermoplastic resin such as a rubber particle binder having an acrylate unit may be used. In such a binder, an acrylate monomer having a reactive functional group introduced thereinto or an acrylate oligomer may be mixed. As the solvent for the positive electrode, a nonaqueous solvent such as N-methyl pyrrolidone may be used. 
       FIG. 1  shows an electrode plate manufacturing apparatus. 
     In a first step, this positive electrode composite material is continuously extruded with a constant width and a constant thickness from a die  24  onto a roll  20  (surface roughness Ra=high) under an extruding pressure of a kneading extruder or a gear pump. The positive electrode composite material extruded onto the roll  20  is extruded onto a surface of the current collector plate  2 . The viscosity of the wet positive electrode composite material in the form of clay is set to 1000 Pa·s or more, which is the most suitable viscosity for the positive electrode composite material to be properly pressure-bonded to the surface of the current collector plate  2 . An arrow shown on the end surface of the roll  20  indicates the direction of rotation of the roll  20 . 
     In a second step, the positive electrode composite material extruded onto the roll  20  is rolled between the roll  20  and a roll  21  disposed in opposition to the roll  20  and having a surface roughness smoother than that of the roll  20  (surface roughness Ra=medium), so as to have a constant thickness. If the thickness of the film of a composite material layer  1  made in the first step is “1”, the material is rolled by the roll  20  and the roll  21  until the thickness becomes not smaller than 0.4 and not larger than 0.6, specifically, 1 mm or less. 
     At this time, the end surfaces of the positive electrode composite material supplied onto the surface of the current collector plate  2  are formed by regulator plates  23   a  and  23   b  disposed between the roll  20  and the roll  21  at opposite ends of the roll  20  and the roll  21  and by regulator plates  23   c  and  23   d  (not shown in  FIG. 1 ; see  FIG. 2 ) disposed between the roll  21  and the current collector plate  2  at opposite ends of the roll  21  so that the slopes of the end surfaces are within the range of specified values.  FIG. 2  shows a cross section of the composite material layer  1  passing through between the regulator plates  21   c  and  23   d.    
     The roll  20  in the second step has, due to its surface roughness, a smaller area of contact with the film of the composite material layer  1  and higher releasability than the roll  21  having medium surface roughness. Accordingly, transfer from the roll  20  having “high” surface roughness to the roll  21  having “medium” surface roughness accompanying the shaping of the film of the composite material layer  1  is performed. 
     If the composite material layer  1  is compressed to have a thickness smaller than “0.4” with respect to the thickness  1  of the film of the composite material layer  1  made in the first step, a pressure acting on the stretch of the film of the composite material layer  1  abnormally increases; both adhesion to the roll  20  having “high” surface roughness and adhesion to the roll  21  having “medium” surface roughness increase; and the film of the composite material layer  1  adheres both to the roll  20  and to the roll  21 , resulting in a rupture of the film of the composite material layer  1 . 
     In a third step, the positive electrode composite material having passed the regulator plates  23   a ,  23   b ,  23   c , and  23   d  is supplied between the roll  21  and the current collector plate  2 . An arrow shown on the end surface of the roll  22  indicates the direction of rotation of the roll  22 . The current collector plate  2  is transported by the roll  22 . 
     The roll  21  having medium surface roughness has, due to its surface roughness, a smaller area of contact with the film of the composite material layer  1  and higher releasability than the current collector plate  2 . Accordingly, the composite material layer  1  is pressure-bonded to and laminated on the current collector plate  2  having higher adhesion to the film of the wet composite material layer  1  than that to the roll  21 , by the roll  22  opposed to the roll  21 . 
     Subsequently, drying is performed by a hot-air drying furnace or the like to complete the positive electrode plate  6  having the composite material layer  1  adhered onto the current collector plate  2 . 
     The most suitable viscosity of the composite material in the first step is 1000 Pa·s or more where the suitably formed shape can be maintained. Due to ease of dispersing and kneading with a planetary mixer or an extruder, extruding of the film of the composite material layer  1  with the die  24  and shaping with the high-surface-roughness roll  20 , the medium-surface-roughness roll  21  and the roll  22 , it is desirable that the viscosity is equal to or lower than 50000 Pa·s. 
       FIG. 3  shows an enlarged perspective view of the completed positive electrode plate  6  in strip form. 
     Tips  23   p  of the regulator plates  23   c  and  23   d  are set in contact with the current collector plate  2  at a distance of L inward from the sides along the longitudinal direction of the current collector plate  2 . Two end surfaces  25   a  and  25   b  of the composite material layer  1  along the longitudinal direction of the current collector plate  2  in the positive electrode plate  6  have, as a result of formation with the regulator plates  23   a ,  23   b ,  23   c , and  23   d  during the rolling in the second step, a slope (X/Z) in the thickness direction as expressed by 
       0&lt;( X/Z )≦1
 
     where Z is the thickness of the end surface of the composite material layer  1  and X is a distance between a perpendicular from the end of the surface of the composite material layer  1  to the current collector plate  2  and the edge of the end surface of the composite material layer  1 . 
     Thus, in the case of manufacture of the positive electrode plate  6  retaining a larger amount of an active material and having the increased thickness Z for the purpose of manufacturing a high-capacity nonaqueous secondary battery, a favorable positive electrode plate  6  can be obtained by shaping the slope profiles of the end surfaces  25   a  and  25   b  of the composite material layer  1  contacting plain portions  2   a  of the current collector plate  2  with the regulator plates  23   a ,  23   b ,  23   c , and  23   d , without executing operations processes such as removing an unnecessary portion with a slitter in a separate process or applying a masking tape on a portion to be formed as the plain portion  2   a  of the current collector plate  2  before the application of the positive electrode composite coating material and separating the masking tape after the completion of the application of the positive electrode composite coating material. 
     On the other hand, in the preparation of the negative electrode plate  7 , a metal foil having a thickness of 5 μm to 25 μm and formed of copper or a copper alloy may be used as the current collector plate  2 . The composite material in the case of the negative electrode plate  7  is made by mixing and dispersing in a dispersion medium a negative electrode active material, a binder and, if necessary, an electroconductive material and a viscosity increasing agent by use of a disperser such as a planetary mixer or an extruder. 
     As the negative electrode active material, various natural graphite, artificial graphite, silicon-based composite materials such as silicide and various alloy composition materials may be used. As the negative electrode binder at this time, various binders including PVdF and a compound obtained by modifying the same may be used. From the viewpoint of improvement in the lithium ion receptivity, however, it can be said more preferable to use in combination or add a small amount of a cellulose resin or the like, e.g., carboxymethyl cellulose (CMC) to styrene-butadiene copolymer rubber particles (SBR) and a material obtained by modifying the same. 
     As the solvent for the negative electrode, a nonaqueous solvent such as N-methyl pyrrolidone and an aqueous solvent may be used. 
     The invention will be described in more details with respect to specific examples thereof. 
     Example 1 
     2 cc (10 g) of lithium cobalt oxide as a positive electrode active material, 0.9 cc (2 g) of acetylene black as an electroconductive material and 25 cc (25 g) of a binder solution prepared by diluting a PVdF powder with N-methyl pyrrolidone to 8% were first mixed and agitated for 30 minutes at a rate of 3000 rpm with a disperser. 18 cc (90 g) of lithium cobalt oxide was thereafter added and the mixture was dispersed and kneaded for 30 minutes with a planetary mixer until its viscosity became 40 kPa·s. A positive electrode composite coating material was thus obtained. 
     In this case, the total amount of the active material was the sum of 2 cc of lithium cobalt oxide and 18 cc of lithium cobalt oxide, i.e., 20 cc; the amount of the binder was 25 cc×0.08, i.e., 2 cc; and the amount of the electroconductive material was 0.9 cc. Finally, a favorable result was obtained when the proportion by volume of the binder was “10” or less to “100” by volume of the active material and when the proportion by volume of the electroconductive material was “10” or less to the proportion “100” by volume of the active material. The amount of the binder is sufficient for bonding the film when the proportion is “10”. A surplus amount of the binder beyond this value is unnecessary. If the amount of the electroconductive material is smaller than “4.5”, the electroconductivity is so low that a desired function cannot be performed. 
     Next, in the first step, the positive electrode composite material was pressurized by extrusion at 50 N in the direction of the arrow in  FIG. 5  using the die  24  having a straight passage. The straight passage changes gradually in shape from an inlet  24   a  in a cylindrical form to an outlet  24   b  in a laterally-extended rectangular tubular form as shown in  FIG. 5 , and has a low passage resistance. A film of the composite material layer  1  having a thickness of 1.5 mm and a width of 25 mm was thus extruded onto the roll  20  having “high” surface roughness Ra (Ra=0.55 μm). 
     Next, in the second step, the regulator plates  23   a  and  23   b  were set at intervals of 30 mm on the roll  21  having “medium” surface roughness Ra (Ra=0.24 μm); the roll  20  and the roll  21  were fixed so as to oppose each other with a constant gap spacing of 0.75 mm set therebetween so that the thickness of the composite material layer  1  was 0.8 mm; and the composite material layer  1  was transferred onto the roll  21 . 
     Next, in the third step, the regulator plates  23   c  and  23   d  were set at intervals of 30 mm on the roll  21 ; the roll  22  was fixed so as to be opposed to the roll  21  with a constant gap spacing of 0.18 mm set therebetween; and the film of the composite material layer  1  was pressure-banded and rolled in the longitudinal direction to the current collector plate  2  formed of aluminum foil having a thickness of 15 μm and “low” surface roughness Ra (Ra=0.17 μm) on the roll  22  while the dimension in the width direction is regulated with the regulator plates  23   c  and  23   d , the thickness of the composite material layer  1  being set to 0.2 mm. A positive electrode plate was obtained, as a nonaqueous secondary battery electrode plate in Embodiment 1, by this rolling and drying at 80° C. in a hot-air drying furnace.  FIG. 6  shows a sectional view of an end portion  1   a  on two longer sides of the nonaqueous secondary battery electrode plate in Embodiment 1. 
     Comparative Example 1 
     2 cc (10 g) of lithium cobalt oxide as a positive electrode active material, 0.9 cc (2 g) of acetylene black as an electroconductive material, 25 cc (25 g) of a binder solution prepared by diluting a PVdF powder with N-methyl pyrrolidone to 8% and 23 cc (23 g) of N-methyl pyrrolidone were first mixed and agitated by a disperser for 30 minutes at a rate of 3000 rpm. 18 cc (90 g) of lithium cobalt oxide was thereafter added and the mixture was dispersed and kneaded for 30 minutes with a planetary mixer until the viscosity became 10 Pa·s. A positive electrode composite coating material was thus obtained. 
     Next, the positive electrode composite coating material was applied on 15 μm aluminum foil by a die to have a film thickness of 0.4 mm and dried at 80° C. The thickness of the composite material layer  1  was set to 0.2 mm. A positive electrode plate  6  was thus obtained as a nonaqueous secondary battery electrode plate in Comparative Example 1. 
       FIG. 7  shows a sectional view of the end portion  1   a  on each of two longer sides of the nonaqueous secondary battery electrode plate in Comparative Example 1. 
     A comparison will be made between the positive electrode plate  6  of Example 1 shown in  FIG. 6  and the positive electrode plate  6  of Comparative Example 1 shown in  FIG. 7 . 
     Each of the end portions  25   a  and  25   b  of the composite material layer  1  contacting the plain portion  2   a  of the current collector plate in the positive electrode plate  6  shown in  FIG. 6  is uniform in thickness to the end portion  1   a  of the composite material layer  1  on each of the two longer sides of the electrode plate and has a slope (X/Z) of (1/1), so that the electrode group can be wound without any gap associated with a variation in the thickness of the electrode plate to form a battery as shown in  FIG. 4 , thereby realizing a battery of high capacity with improved safety. 
     On the other hand, in the case of the positive electrode plate  6  having the coating material applied thereon with a die, the coating material exhibiting liquid behavior at a viscosity of 10 Pa·s protrudes due to a surface tension in the end portion of the composite material layer  1  contacting the plain portion  2   a  of the current collector plate in the positive electrode plate  6  shown in  FIG. 7 , and the protrusion remains even after drying. As a result, the slope (X/Z) is about “5 to 6” and a protrusion exists at the vertex of the end portion la of the composite material layer. In a case where the electrode group is formed by using the positive electrode plate  6  in Comparative Example 1, gaps are formed in association with variations in the thickness of the electrode plate to reduce the amount of the filled active material per unit volume contributing to the charge/discharge of lithium ions. As a result, it is difficult to provide a battery of high capacity. A portion of the electrode plate end portion increased in thickness due to a surface tension may be removed by slitting or the like, and an electrode plate may be formed by the other portion uniform in thickness. However, the composite material layer inevitably comes off at the time of slitting, and the composite material layer partly attaches to and remains on the electrode plate end portion when the composite material layer comes off. There is concern that such a chip of the composite material layer may pierce the separator  8  in the battery to cause an internal short circuit. Further, a material of a higher surface tension may be rounded in the end portion thereof so that the slope (X/Z) is “2 to 4”. However, needless to say, the electrode plate end portion protrudes due to the higher surface tension, so that the thickness of the electrode plate end portion is larger than that shown in Comparative Example 1. The thickness of the electrode plate end portion may be larger than that in Comparative Example 1, thereby further reducing the amount of the filled active material. It is desirable that the slope (X/Z) be (1/1) or less. If X is infinitely closer to “0”, the volume of the composite material layer  1  can be maximized. Accordingly, the amount of the filled active material can be maximized. Conversely, if X becomes minus, the end portion  1   a  is inwardly recessed and the volume of the composite material layer  1  is reduced. It is therefore desirable that 0≦X. Consequently, it is also desirable that the slope (X/Z) satisfy “0≦(X/Z)”. 
     Embodiment 2 
       FIGS. 8 and 9  show Embodiment 2 of the present invention. 
     In Embodiment 1, a battery is formed by winding the positive electrode plate  6  and the negative electrode plate  7  in spiral form with the separator  8  interposed therebetween and housing them in the battery case  11 . However, the electrode plate made in Embodiment 1 as the positive electrode plate  6  or the negative electrode plate  7  can also be used in a battery in which, as shown in  FIG. 8 , a positive electrode plate  6  having a composite lithium oxide as an active material and a negative electrode plate  7  having as an active material a material capable of retaining lithium are stacked one on top of another with a separator  8  interposed therebetween, and an opening of a laminate container  18  aluminum foil-laminated with an insulating resin is sealed by ultrasonic welding while one end of a positive electrode lead  15  and one end of a negative electrode lead  16  are led to the outside, the positive electrode lead  15  having the other end connected to the positive electrode plate  6  and the negative electrode lead  16  having the other end connected to the negative electrode plate  7 . 
     In this case, each electrode plate is made by cutting the lengthwise electrode plate made in Embodiment 1 into pieces of required length in the lengthwise direction thereof, as shown in  FIG. 9 . 
     Embodiment 3 
       FIGS. 10 to 12  show Embodiment 3 of the present invention. 
     In Embodiment 1, the plain portions  2   a  and  2   b  where the composite material layer  1  is not laminated and the surface of the current collector plate  2  in the electrode plate is exposed, are formed in the current collector plate  2  on the sides of the same along the longitudinal direction of the same, the electrode plate forming the positive electrode plate  6  and the negative electrode plate  7 . This is applicable to an electrode plate of a battery shown in  FIG. 10 . 
     In this battery using an electrode plate not provided with plain portions, an electrode group  14  is made by winding in spiral form a positive electrode plate  6  having a composite lithium oxide as an active material and a negative electrode plate  7  having a material capable of retaining lithium as an active material, with a separator  8  interposed therebetween. 
     Next, the electrode group  14  is housed with an insulating plate  17  in a battery case  11  in the form of a cylindrical tube closed at the bottom thereof. A negative electrode lead  16  led out from the lower portion of the electrode group  14  is thus connected to the bottom portion of the battery case  11 . 
     Next, a positive electrode lead  15  led out from the upper portion of the electrode group  14  is connected to a sealing plate  12 . 
     An electrolytic solution (not shown) composed of a predetermined quantity of a nonaqueous solvent is injected into the battery case  11 . The sealing plate  12  having a sealing gasket  13  attached to the peripheral end portion thereof is thereafter inserted in the opening portion of the battery case  11 , and the opening portion of the battery case  11  is inwardly bent for caulk sealing. 
       FIG. 11  shows the electrode plate in this case. A plain portion  3  is formed in the width direction of a current collector plate  2  in the vicinity of the end portion of the electrode plate. The plain portion  3  is connected to the sealing plate  12  by the positive electrode lead  15  in the case of the positive electrode plate  6 . The plain portion  3  is connected to the battery case  11  by the negative electrode lead  16  in the case of the negative electrode plate  7 . 
     The same advantage as that of the electrode plate having plain portions along the longer sides thereof shown in  FIG. 3  can be expected when a composite material layer  1  is formed such that the slope in the thickness direction (X/Z) of the end surfaces along the longer sides of the current collector plate  2  satisfies “0≦(X/Z)≦1”. 
     The electrode plate shown in  FIG. 11  can be made by the manufacturing apparatus shown in  FIG. 1 , as described below. Specifically, as shown in  FIG. 12 , tips  23   p  of regulator plates  23   c  and  23   d  are brought into direct contact with the surface of a roll  22 , and the current collector plate  2  is brought into contact with sloped surfaces  23   r  of the regulator plates  23   c  and  23   d . In this state, the current collector plate  2  is transported. To form the plain portion  3  to which the positive electrode lead  15  or the negative electrode lead  16  is connected, a portion of the composite material layer  1  laminated on the current collector plate  2  is removed with a scraping plate or a suction nozzle before drying such that the surface of the current collector plate  2  is exposed. 
     Embodiment 4 
     In the embodiments described above, the composite material layer  1  is formed on one surface of the current collector plate  2  in the electrode plate such that the slope in the thickness direction (X/Z) of the end surfaces along the longer sides of the current collector plate  2  satisfies “0&lt;(X/Z)≦1”. However, the composite material layers  1  can be formed at a time on both surfaces of the current collector plate  2  by using a manufacturing apparatus shown in  FIG. 13 . 
     In the manufacturing apparatus shown in  FIG. 13 , a die  24 , rollers  20  and  21  and regulator plates  23   a  to  23   d  are disposed in the same way as shown in  FIG. 1  on each side of the current collector plate  2  transported downward from above to simultaneously perform the same processes including the first to third steps on each side of the current collector plate  2  and drying, thereby forming composite material layers  1  on both surfaces of the current collector plate  2 . 
     In the above-described embodiments, the slope in the thickness direction (X/Z) of the end surfaces along the longer sides of the current collector plate in the composite material layer formed on the surface of the current collector plate is preferably “0&lt;(X/Z)≦1”. More preferably, the slope (X/Z) is “0.2≦(X/Z)≦1”. In the battery manufacturing process, if the electrolytic solution is injected through the side end surface of the electrode plate to permeate the electrode plate, the permeability of the electrolytic solution to the entire electrode plate is higher when “0.2≦(X/Z)≦1” than when “0&lt;(X/Z)&lt;0.2”. When “0.2≦(X/Z)≦1”, charge/discharge reaction nonuniformity in the electrode plate is reduced and the life property is improved. Therefore such a condition is preferable. Experimentally, electrode plates shown in  FIGS. 17(   a ) and  17 ( b ), in which the slope (X/Z) was changed in the range from 0 to 1, were used in a plurality of batteries and were impregnated with an electrolytic solution by injecting the electrolytic solution through the side end surface of the electrode plate. After the impregnation with the electrolytic solution, the batteries were disassembled and a portion A impregnated with the electrolytic solution and a portion B not impregnated with the electrolytic solution were examined. The electrode plate area ratio A/(A+B) of the portion impregnated with the electrolytic solution was computed for each electrode.  FIG. 18  shows the results of this computation. 
     As can be understood from  FIG. 18 , the number of portions B not impregnated with the electrolytic solution was large in the range of “0&lt;(X/Z)&lt;0.2” and the electrode plate area ratio of the portion impregnated with the electrolytic solution was about 72.0% to slightly less than 99% in this range. In contrast, in the range of “0.2&lt;(X/Z)≦1”, the proportion of portions B not impregnated with the electrolytic solution was 99.0% to 99.9% and the permeation of the electrolytic solution was remarkably good. 
     The slopes (X/Z) of the two end surfaces are equally set to 45° as shown in  FIG. 2 , the slope of one of the end surfaces and the slope of the other may differ from each other if the slope is within the range of “0&lt;(X/Z)≦1”, more preferably within the range “0.2≦(X/Z)≦1”. 
     INDUSTRIAL APPLICABILITY 
     The present invention can contribute to an improvement in safety and an increase in capacity of nonaqueous secondary batteries. 
     REFERENCE SIGNS LIST 
     
         
         Z Distance between surface of composite material layer and current collector plate 
         X Distance from perpendicular extending from end of surface of composite material layer to the current collector plate 
           1  Composite material layer 
           1   a  End portion of composite material layer 
           2  Current collector plate 
           3  Plain portion 
           6  Positive electrode plate 
           7  Negative electrode plate 
           8  Separator 
           9  Positive electrode current collector plate 
           10  Negative electrode current collector plate 
           11  Battery case 
           12  Sealing plate 
           13  Gasket 
           14  Electrode group 
           15  Positive electrode lead 
           16  Negative electrode lead 
           17  Insulating plate 
           18  Laminate container 
           20 ,  21 ,  22  Roll 
           23   a ,  23   b ,  23   c ,  23   d  Regulator plate 
           24  Die