Patent Publication Number: US-2020295353-A1

Title: Electrode sheet manufacturing method

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2019-046358 filed on Mar. 13, 2019 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electrode sheet manufacturing method. More specifically, the present disclosure relates to an electrode sheet manufacturing method for manufacturing an electrode sheet by forming an electrode mixture layer on a surface of a current collector foil while conveying the current collector foil. 
     2. Description of Related Art 
     Some rechargeable batteries such as lithium ion rechargeable batteries have positive and negative electrode sheets thereinside. Specifically, for example, positive and negative electrode sheets are stacked by being wound or flat-stacked with separators interposed between them, and then are housed in cases. An example of the manufacturing method of the above electrode sheet of related art may include, for example, Japanese Patent Application Publication No. 2016-119207 (JP 2016-119207 A). 
     JP 2016-119207 A describes that an electrode mixture layer is formed by supplying and depositing particles used for forming an electrode mixture layer on a current collector foil, and then pressing the layer of the deposited particles in the thickness direction. 
     SUMMARY 
     Meanwhile, in the above related art, granulated particles are used as particles used for forming the electrode mixture layer. Granulated particles are produced by kneading an active material and a binder, which are powder materials for forming the electrode mixture layer, with a solvent as a liquid component, and the like, and the granulated particles therefore contain the solvent. 
     However, the solvent is an unnecessary component in a finished electrode sheet. Hence, when granulated particles containing the solvent are used, drying for removing the solvent is required in a subsequent step, and the drying step may take a long time. Consequently, the related art has such a problem that the manufacture efficiency of the electrode sheet becomes deteriorated. 
     The present disclosure has been made for the purpose of solving the above-described problem of the related art. The present disclosure provides a manufacturing method of an electrode sheet which can efficiently manufacture a high-quality electrode sheet. 
     An electrode sheet manufacturing method of the present disclosure, which has been made for the purpose of solving the above problems, is an electrode sheet manufacturing method manufacturing an electrode sheet by forming an electrode mixture layer on a surface of a current collector foil while conveying the current collector foil, the electrode mixture layer made of an electrode mixture material including at least an active material and a binder, the electrode sheet manufacturing method including: an applying step of applying the electrode mixture material on a formation surface that is a surface of the current collector foil on which the electrode mixture layer is formed; and a heating-pressing step of heating and pressing a layer of the electrode mixture material applied on the formation surface in a thickness direction of the layer of the electrode mixture material. In the applying step, by means of a backup roll and a supply roll, the backup roll rotating and in contact with a back surface of the current collector foil opposite to the formation surface of the current collector foil, the supply roll facing the backup roll with the current collector foil interposed between the supply roll and the backup roll, the supply roll arranged with a gap between the formation surface and the supply roll, the supply roll is rotated while the electrode mixture material is supplied in a powder state on a surface of the supply roll, a potential difference is produced between the backup roll and the supply roll, and the electrode mixture material is moved from the surface of the supply roll to the formation surface by an electrostatic force acting between the electrode mixture material and the current collector foil so as to apply the electrode mixture material on the formation surface. The applying step is performed multiple times before the heating-pressing step. 
     In the electrode sheet manufacturing method according to the present disclosure, the electrode mixture material can be applied in a powder state on the formation surface of the current collector foil. That is, unlike the case of the related art, a material that does not contain a solvent can be used, so that a step for removing the solvent can be eliminated. Further, by performing the applying step multiple times, it is possible to apply a sufficient amount of the electrode mixture material on the current collecting foil while increasing the conveying speed of the current collecting foil. Thereby, a high-quality electrode sheet can be manufactured efficiently. 
     In the above electrode sheet manufacturing method according to the present disclosure, of the multiple applying steps, in the applying step performed last time, an active material having a smaller average particle diameter than that used in the applying step performed before the applying step performed last time may be used as the active material. This is because a higher quality electrode sheet can be manufactured in which the average particle diameter of the active material present near the surface of the electrode mixture layer is small. 
     According to the present disclosure, provided is the electrode sheet manufacturing method which can efficiently manufacture a high-quality electrode sheet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a sectional view of an electrode sheet according to an embodiment; 
         FIG. 2  is a schematic configuration view of an electrode manufacturing apparatus according to an embodiment; and 
         FIG. 3  is a view showing powder of an electrode mixture material in a stirring container of the electrode manufacturing apparatus. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, best modes for embodying the present disclosure will be described in detail with reference to the drawings. 
     First, an electrode sheet manufactured by the manufacturing method according to the present embodiment will be described.  FIG. 1  is a sectional view of an electrode sheet  10  according to the present embodiment. The electrode sheet  10  has a sheet-like shape as a whole having its longitudinal direction in the left-right direction. The electrode sheet  10  has a current collector foil  20  and an electrode mixture layer  30  in the thickness direction that is the height direction in  FIG. 1 . The above-configured electrode sheet  10  is used as an electrode of a rechargeable battery, for example. In the present embodiment, the electrode sheet  10  used as a negative electrode of a lithium ion rechargeable battery will be described. 
     The current collector foil  20  has a first surface  21  that is one surface in the thickness direction and a second surface  22  that is a back surface of the first surface  21 . 
     In the electrode sheet  10  of the present embodiment that is a negative electrode of a lithium ion rechargeable battery, a copper foil can be used as the current collector foil  20 , for example. 
     The electrode mixture layer  30  is provided so as to cover the first surface  21  of the current collector foil  20 . In  FIG. 1 , the surface of the electrode mixture layer  30  farther from the current collector foil  20  is shown as an electrode mixture layer surface  31 . The electrode mixture layer  30  is made of an electrode mixture material  40 . As the electrode mixture material  40 , the electrode mixture layer  30  of the present embodiment includes at least an active material  41  and a binder  42 . 
     The active material  41  is a material that can occlude and release lithium ions. The binder  42  is a material used for forming the electrode mixture layer  30  by causing mutual binding in the active material  41 . and also binding the electrode mixture layer  30  onto the first surface  21  of the current collector foil  20 . In the electrode sheet  10  of the present embodiment, which is the negative electrode of the lithium ion rechargeable battery, graphite can be used as the active material  41  and PVdF can be used as the binder  42 , for example. 
     Next, the manufacturing method of the electrode sheet  10  will be described.  FIG. 2  is a schematic configuration view of an electrode manufacturing apparatus  100  capable of manufacturing the electrode sheet  10  of the present embodiment. 
     As shown in  FIG. 2 , the electrode manufacturing apparatus  100  can manufacture the electrode sheet  10  while conveying the elongate current collector foil  20  in the longitudinal direction. In  FIG. 2 , the current collector foil  20  is supplied to the electrode manufacturing apparatus  100  from the lower right side. In the present embodiment, the first surface  21  of the current collector foil  20  being supplied to the electrode manufacturing apparatus  100  is not yet formed with anything, and thus the first surface  21  is exposed. While conveying the current collector foil  20  along a conveyance path F, the electrode manufacturing apparatus  100  discharges the current collector foil  20  from the upper right side as the electrode sheet  10  having the electrode mixture layer  30  formed on the first surface  21  thereof. Further, on the conveyance path F of the current collector foil  20  being conveyed in the electrode manufacturing apparatus  100 , a first applying position A, a second applying position B, and a heating-pressing position C are provided in this order from upstream to downstream in a conveyance direction FD. 
     In the first applying position A, a backup roll  120 A and a supply roll  130 A are provided to face each other with the current collector foil  20  interposed therebetween. The backup roll  120 A rotates in a direction indicated by an arrow shown in  FIG. 2  (clockwise) while the outer peripheral surface thereof is in contact with the second surface  22  of the current collector foil  20 . Thereby, the current collector foil  20  can be conveyed. The supply roll  130 A rotates in a direction indicated by an arrow shown in  FIG. 2  (counterclockwise) while the outer peripheral surface thereof is out of contact with the first surface  21  of the current collector foil  20 . That is, the supply roll  130 A is arranged with a gap between the current collector foil  20  and the supply roll  130 A. Further, the supply roll  130 A of the present embodiment is a magnet roll that can attract a ferromagnetic material. 
     A power supply  160 A is electrically connected to the backup roll  120 A and the supply roll  130 A. Accordingly, the power supply  160 A can produce a potential difference between the backup roll  120 A and the supply roll  130 A. 
     A stirring unit  140 A is provided below the supply roll  130 A. The stirring unit  140 A can stir an object accommodated in a stirring container  145 A by rotation of stirring blades  141 A,  142 A. A squeegee  143 A that protrudes toward the supply roll  130 A is provided at an upper right part of the stirring container  145 A. The front end of the squeegee  143 A is out contact with the supply roll  130 A, and a gap is provided between the squeegee  143 A and the supply roll  130 A. 
     A powder feeding unit  150 A is provided on the upper left side of the stirring unit  140 A. The powder feeding unit  150 A is a unit into which the electrode mixture material  40  is fed. The active material  41  and the binder  42  as the electrode mixture material  40  are fed in a powder state into the powder feeding unit  150 A. In the present embodiment, the electrode mixture material  40  in a state of containing no solvent is fed into the powder feeding unit  150 A. 
     The powder feeding unit  150 A is configured to feed the powder of the fed electrode mixture material  40  into the stirring container  145 A from below, as indicated by an arrow XA. Hence, the powder of the electrode mixture material  40  is accommodated in the stirring container  145 A.  FIG. 3  is a view showing the powder of the electrode mixture material  40  in the stirring container  145 A.  FIG. 3  also shows the supply roll  130 A disposed above the stirring unit  140 A. Further, as shown in  FIG. 3 , carrier particles  131  are also accommodated in the stirring container  145 A. The carrier particles  131  are ferromagnetic particles. As the carrier particles  131 , ferrite particles can be used, for example. 
     Some of the carrier particles  131  in the stirring container  145 A adhere to the supply roll  130 A that is a magnet roll, as shown in  FIG. 3 . In addition, the particles of the electrode mixture material  40  being stirred in the stirring container  145 A adhere to the carrier particles  131 . The electrode mixture material  40  adheres to the carrier particles  131  due to the van der Waals force or by being caught on the carrier particles  131 . 
     Specifically, as indicated by an arrow YA in  FIG. 2 , the powder of the electrode mixture material  40  in the stirring container  145 A adheres to the supply roll  130 A via the carrier particles  131 . In addition, as described above, the supply roll  130 A is rotated in the direction indicated by the arrow in  FIG. 2 . Hence, the carrier particles  131  and the electrode mixture material  40  adhering to the supply roll  130 A reach the squeegee  143 A provided with a gap between the supply roll  130 A and the squeegee  143 A by the rotation of the supply roll  130 A. The squeegee  143 A can level the carrier particles  131  and the electrode mixture material  40  on the supply roll  130 A passing the squeegee  143 A. That is, the carrier particles  131  and the electrode mixture material  40  on the supply roll  130 A having reached the squeegee  143 A are leveled as passing through the gap between the supply roll  130 A and the squeegee  143 A, to thereby adjust the adhesion amount thereof to be constant. 
     The carrier particles  131  and the electrode mixture material  40  whose adhesion amount to the supply roll  130 A is adjusted at a constant level reach the first applying position A as the supply roll  130 A further rotates. At the first applying position A, a potential difference is produced between the backup roll  120 A and the supply roll  130 A by the power supply  160 A. Consequently, a potential difference is also produced between the current collector foil  20  in contact with the backup roll  120 A and the powder of the electrode mixture material  40  adhering to the supply roll  130 A. Accordingly, at the first applying position A, an electrostatic force acts between the current collector foil  20  and the power of the electrode mixture material  40 . 
     A tension for the conveyance is applied to the current collector foil  20 , and by the tension, a pushing force is applied to the current collector foil  20  at the first applying position A in a direction of pushing the current collector foil  20  against the backup roll  120 A. On the other hand, the adhesion strength of the powder of the electrode mixture material  40  onto the supply roll  130 A is caused due to the van der Waals force or by being caught on the carrier particles  131  as described above. That is, the adhesion strength of the powder of the electrode mixture material  40  onto the supply roll  130 A is weaker than the pushing force of the current collector foil  20  against the backup roll  120 A. Therefore, at the first applying position A, due to the electrostatic force acting between the current collector foil  20  and the powder of the electrode mixture material  40 , the powder of the electrode mixture material  40  jumps to move from the supply roll  130 A to the first surface  21  of the current collector foil  20 , as indicated by an arrow ZA. Thereby, at the first applying position A, the powder of the electrode mixture material  40  can be caused to adhere and be applied on the first surface  21  of the current collector foil  20 . 
     The carrier particles  131  on the supply roll  130 A remain on the supply roll  130 A due to an attractive force generated by a magnetic force of the supply roll  130 A. That is, the electrostatic force acting in the direction of the arrow ZA on the carrier particles  131  at the first applying position A is weaker than the attractive force caused by the magnetic force of the supply roll  130 A. The carrier particles  131  remaining on the supply roll  130 A are then returned to the stirring container  145 A by the rotation of the supply roll  130 A. Alternatively, the carrier particles  131  adhering on the supply roll  130 A passes through the squeegee  143 A and the first applying position A again, while allowing the powder of the electrode mixture material  40  to adhere thereon. 
     At the second applying position B, the same configuration as that at the first applying position A is employed. That is, at the second applying position B, a backup roll  120 B and a supply roll  130 B are also provided to face each other with the current collector foil  20  interposed therebetween. A power supply  160 B is electrically connected to the backup roll  120 B and the supply roll  130 B so as to produce a potential difference therebetween. A stirring unit  140 B is provided below the supply roll  130 B, and a powder feeding unit  150 B is provided on the upper left side of the stirring unit  140 B. Also in the powder feeding unit  150 B, the electrode mixture material  40  in a powder state of containing no solvent is fed. 
     Then, the powder of the electrode mixture material  40  fed in the powder feeding unit  150 B is supplied into a stirring container  145 B as indicated by an arrow XB. The electrode mixture material  40  supplied from the powder feeding unit  150 B into the stirring container  145 B is stirred by the rotating stirring blades  141 B,  142 B, and is moved to the supply roll  1309  to which the carrier particles  131  adhere, as indicated by an arrow YB. The powder of the electrode mixture material  40  adhering to the supply roll  1309  reaches the second applying position B after the adhesion amount thereof is adjusted by the squeegee  143 B by the rotation of the supply roll  130 B. 
     At the second applying position B, a potential difference is produced between the current collector foil  20  on the backup roll  120 B side and the powder of the electrode mixture material  40  on the supply roll  130 B side by the power supply  160 B. The electrode mixture material  40  moves from the supply roll  130 B side toward the current collector foil  20  side, as indicated by an arrow ZB by an electrostatic force acting due to this potential difference. That is, also at the second applying position B, the electrode mixture material  40  can be caused to adhere and applied onto the first surface  21  side of the current collector foil  20 . As described above, at the second applying position B, since the same configuration as that at the first applying position A is provided, the electrode mixture material  40  can be applied onto the first surface  21  of the current collector foil  20 , as with the first applying position A. 
     The powder of the electrode mixture material  40  applied on the current collector foil  20  at the first applying position A and at the second applying position B can be caused to adhere to the first surface  21  of the current collector foil  20  by the van der Waals force. Therefore, the electrode mixture material  40  can be held on the first surface  21  even when the first surface  21  of the current collector foil  20  faces downward in the gravity direction. 
     A hot press roll pair  190  is provided at a heating-pressing position C located more downstream than the second applying position B in the conveyance direction FD of the current collector foil  20 . The hot press roll pair  190  includes a first hot press roll  191  and a second hot press roll  192  that are provided to face each other. That is, the heating-pressing position C is a position where the first hot press roll  191  and the second hot press roll  192  face each other. 
     The first hot press roll  191  and the second hot press roll  192  are arranged with a predetermined distance therebetween at the heating-pressing position C. The dimension of the gap between the hot press roll pair  190  is smaller than a total combined thickness of the thickness of the current collector foil  20  and the thickness of the powder layer of the electrode mixture material  40  on the first surface  21  at a position before passing through the heating-pressing position C. Therefore, as passing through the heating-pressing position C, the powder layer of the electrode mixture material  40  adhering on the first surface  21  of the current collector foil  20  is pressed together with the current collector foil  20  in the thickness direction. 
     The hot press roll pair  190  may have any configuration as long as the hot press roll pair  190  can press, in the thickness direction, the current collector foil  20  and the powder layer of the electrode mixture material  40  on the first surface  21  of the current collector foil  20  when they pass through the heating-pressing position C. Therefore, the hot press roll pair  190  may be configured such that a pushing force oriented in the opposite direction may be applied to at least one of the first hot press roll  191  and the second hot press roll  192 . 
     In addition, at least one of the first hot press roll  191  and the second hot press roll  192  can be heated by a heating source. This heating temperature is set at a temperature at which the binder  42  passing through the heating-pressing position C is softened or melted. That is, the heating temperature is set at a temperature at which the binding action is caused in the binder  42 . Therefore, the current collector foil  20  and the powder of the electrode mixture material  40  adhering on first surface  21  of the current collector foil  20  are heated as they pass through the heating-pressing position C. 
     At the heating-pressing position C, as the electrode mixture material  40  is pressed while being heated, mutual binding is caused in the active material  41  on the first surface  21  of the current collector foil  20  by the binder  42 . Thereby, the electrode mixture layer  30  is formed. The electrode mixture layer  30  is bound onto the first surface  21  of the current collector foil  20  by the binder  42 . That is, the current collector foil  20  to which the powder of the electrode mixture material  40  adheres passes through the heating-pressing position C, to be formed into the electrode sheet  10 . 
     In the present embodiment, the following three steps can be performed in this order by manufacturing the electrode sheet  10  using the above-described electrode manufacturing apparatus  100 : 1, a first applying step; 2. a second applying step; and 3. a heating-pressing step 3. 
     That is, the current collector foil  20  having been conveyed to the electrode manufacturing apparatus  100  first reaches the first applying position A. Then, at the first applying position A, “1. the first applying step” of applying the electrode mixture material  40  on the first surface  21  of the current collector foil  20  is performed. 
     Specifically, an outer peripheral surface of the supply roll  130 A provided below the first applying position A is supplied with the electrode mixture material  40  in a power state by the stirring unit  140 A from the lower side different from the upper side facing the first surface  21  of the current collector foil  20 . The electrode mixture material  40  supplied to the supply roll  130 A is leveled as the electrode mixture material  40  passes through the squeegee  143 A by the rotation of the supply roll  130 A, and thereafter, faces the current collector foil  20  positioned at the first applying position A. 
     Further, a potential difference is produced between the backup roll  120 A and the supply roll  130 A by the power supply  160 A. Therefore, an electrostatic force acts between the current collector foil  20  in contact with the second surface  22  of the backup roll  120 A and the electrode mixture material  40  adhering to the supply roll  130 A. The electrostatic force causes the electrode mixture material  40  to move from the supply roll  130 A to the first surface  21  of the current collector foil  20 . Thereby, at the first applying position A, “1. the first applying step” is performed in which the electrode mixture material  40  is applying on the first surface  21  of the current collector foil  20 . 
     The current collector foil  20  after passing through the first applying position A then reaches the second applying position B. Subsequently, at the second applying position B, “2. the second applying step” is performed in which the electrode mixture material  40  is applied on the first surface  21  of the current collector foil  20 . 
     Also in “2. the second applying step” performed at the second applying position B, the applying method of applying the electrode mixture material  40  itself is the same as that in “1, the first applying step”. However, in “2. the second applying step” performed at the second applying position B, the electrode mixture material  40  is applied on the first surface  21  of the subsequent current collector foil  20  on which the electrode mixture material  40  has already been applied in “1. the first applying step” having been performed at the first applying position A. That is, in “2. the second applying step”, the electrode mixture material  40  is applied to be overlaid on the first surface  21  of the current collector foil  20  to which the electrode mixture material  40  has already been applied. 
     The current collector foil  20  after passing through the second applying position B then reaches the heating-pressing position C. At the heating-pressing position C, “3. the heating-pressing step” is performed in which heating and pressing are performed on the current collector foil  20  and the layer of the electrode mixture material  40  applied on the first surface  21  of the current collector foil  20 . 
     Specifically, at the heating-pressing position C, the current collector foil  20  and the layer of the electrode mixture material  40  applied on the first surface  21  of the current collector foil  20  pass through between the first hot press roll  191  and the second hot press roll  192 . When passing therethrough, the current collector foil  20  and the layer of the electrode mixture material  40  disposed on the first surface  21  of the current collector foil  20  are pressed in the thickness direction thereof. Furthermore, at least one of the first hot press roll  191  and the second hot press roll  192  is heated by a heating source. Hence, at the heating-pressing position C, the current collector foil  20  and the layer of the electrode mixture material  40  disposed on the first surface  21  of the current collector foil  20  are heated. 
     Accordingly, the layer of the electrode mixture material  40  disposed on the first surface  21  of the current collector foil  20  is set to have an appropriate thickness and is fixed onto the first surface  21  with the binding action of the binder  42 . Thereby, it is possible to manufacture the electrode sheet  10  with the electrode mixture layer  30  formed on the first surface  21  of the current collector foil  20 . 
     Here, in the manufacturing method of the electrode sheet  10  of the present embodiment, it is unnecessary to use a solvent for forming the electrode mixture layer  30 . That is, as the powder of the electrode mixture material  40  supplied to the surface of the supply roll  130 A, power containing no solvent can be used. Accordingly, it is unnecessary to remove the solvent later, and the electrode sheet  10  can be manufactured without requiring a special drying step, for example. That is, it is possible to efficiently manufacture the electrode sheet  10 . 
     In the present embodiment, as the step of applying the electrode mixture material  40  on the first surface  21  of the current collector foil  20 , the first applying step and the second applying step are performed. That is, the applying step of applying the electrode mixture material  40  on the first surface  21  of the current collector foil  20  is performed twice. Accordingly, the high-quality electrode sheet  10  can be manufactured efficiently. 
     In the electrode sheet  10 , it is not preferable for the electrode mixture layer  30  to have an excessively thin thickness. This is because there is such a problem that may cause decrease in full charge capacity of a rechargeable battery manufactured using the electrode sheet  10 , or the like. That is, generally, in order to manufacture a high-quality rechargeable battery, the electrode mixture layer  30  in the electrode sheet  10  needs to have a certain thickness. 
     For example, when the applying step is completed once, the electrode mixture material  40  with amount sufficient to form the electrode mixture layer  30  having a desired thickness is applied on the first surface  21  of the current collector foil  20  through the only one applying step. In this case, in the applying step, it is required to provide a sufficient supply amount of the electrode mixture material  40  with respect to the conveyance speed of the current collector foil  20 . Specifically, for example, in order to apply the electrode mixture material  40  with sufficient amount to form the electrode mixture layer  30  having a desired thickness at the first applying position A, there is a method to set the peripheral speed of the supply roll  130 A faster than the peripheral speed of the present embodiment. 
     Meanwhile, in order to increase the peripheral speed of the supply roll  130 A, as the rotational speed of the supply roll  130 A increases, a stronger centrifugal force is applied to the electrode mixture material  40  adhering to the supply roll  130 A. On the other hand, as described above, the adhesion strength of the power of the electrode mixture material  40  to the supply roll  130 A is caused due to the van der Waals force or by being caught on the carrier particles  131 , and thus this is not so strong. Hence, the supply amount of the electrode mixture material  40  to the first applying position A is not necessarily increased in proportion to the rotation speed of the supply roll  130 A. That is, an excessively high rotation speed of the supply roll  130 A rather causes increase in amount of the electrode mixture material  40  that has once adhered to the supply roll  130 A and then comes off and scatters away from the supply roll  130 A. Hence, an excessively high rotation speed of the supply roll  130 A cannot increase the supply amount of the electrode mixture material  40  to the first applying position A so much. In other words, increase in peripheral speed of the supply roll  130 A results in increase in scattering amount of the electrode mixture material  40 , which may deteriorate the productive efficiency of the electrode sheet  10 . 
     For example, the applying amount of the electrode mixture material  40  at the first applying position A can be increased by lowering the conveyance speed of the current collector foil  20 . However, if the conveyance speed of the current collector foil  20  is lowered, the productivity of the electrode sheet  10  is lowered, accordingly, 
     To counter this, in the present embodiment, the applying step of applying the electrode mixture material  40  on the first surface  21  of the current collector foil  20  is performed twice. That is, the electrode mixture material  40  with sufficient amount to form the electrode mixture layer  30  having a desired thickness is applied on the first surface  21  of the current collector foil  20  in two steps. Therefore, in each of the first applying step and the second applying step, the amount of the electrode mixture material  40  applied on the first surface  21  of the current collector foil  20  can be smaller than the amount of the electrode mixture material  40  required for forming the electrode mixture layer  30  having a desired thickness. That is, the conveyance speed of the current collector foil  20  can be maintained at a high level while the supply roll  130 A and the supply roll  130 B are set to have appropriate rotation speeds without having excessively high rotation speeds. Accordingly, in the manufacturing method of the electrode sheet  10  of the present embodiment, it is possible to efficiently manufacture the high-quality electrode sheet  10  having the electrode mixture layer  30  with a sufficient thickness. 
     In the manufacturing method of the electrode sheet  10  of the present embodiment using the electrode manufacturing apparatus  100 , the applying step of applying the powder of the electrode mixture material  40  on the first surface  21  of the current collector foil  20  is performed twice: the first applying step; and the second applying step. Thus, as the electrode mixture material  40 , different materials can be used respectively in the first applying step and the second applying step. 
     In the second applying step, the powder of the electrode mixture material  40  is applied in the state in which the powder of the electrode mixture material  40  is already present on the first surface  21  of the current collector foil  20  in the first applying step. Therefore, in the electrode mixture layer  30  of the electrode sheet  10 , more of the electrode mixture material  40  applied in the first applying step is present near the first surface  21  of the current collector foil  20 , and more of the electrode mixture material  40  applied in the second applying step is present near the electrode mixture layer surface  31 . 
     In the electrode sheet  10 , it is likely to be preferable that particles of the active material  41  present near the electrode mixture layer surface  31  of the electrode mixture layer  30  have small particle diameters. For example, in a lithium ion rechargeable battery in which an electrolytic solution is contained together with the electrode sheet  10  in the case, the smaller the particle diameters of the particles of the active material  41  present near the electrode mixture layer surface  31 , the greater the contact area between the electrolytic solution and the particles of the active material  41  can be. Accordingly, it is likely to enhance the acceptability of lithium ion of the electrode mixture layer  30 , to thereby produce a lithium ion rechargeable battery with a high quality. 
     Therefore, in the manufacturing method of the electrode sheet  10  of the present embodiment, as the active material  41  in the electrode mixture material  40  used in the second applying step, it is preferable to use an active material having a smaller average particle diameter than that of the active material  41  used in the first applying step. Specifically, for example, in the electrode manufacturing apparatus  100 , it is conceivable that the average particle diameter of the powder of the active material  41  fed into the powder feeding unit  150 B according to the second applying step is set to be about ½ of the average particle diameter of the powder of the active material  41  fed into the powder feeding unit  150 A according to the first applying step. As described above, the electrode sheet  10  used for producing a high-quality rechargeable battery can be manufactured by using, as the active material  41  used in the second applying step, a material having a smaller average particle diameter than that of the active material  41  used in the first applying step. In the present embodiment, the average particle diameter is defined based on the median diameter that is a particle diameter of an integrated value of 50% in the particle size distribution based on the volume standard, obtained by the laser diffraction-scattering method. 
     Moreover, in the manufacturing method of the electrode sheet  10  using the above-described electrode manufacturing apparatus  100 , the applying step in which the powder of the electrode mixture material  40  is applied on the first surface  21  of the current collector foil  20  is performed twice (in the first applying step and the second applying step). However, the applying step may be performed three or more times. That is, the applying step may be performed multiple times before the heating-pressing step. When performing the applying step three times, it may be configured to use the active material having a smaller average particle diameter in the third applying step than those used in the first and the second applying steps. That is, when the applying step is performed multiple times, in the last applying step of the multiple times, it may be configured to use such an active material that has a smaller average particle diameter than those used in the applying step performed before the last time. This is because it is possible to manufacture a high-quality electrode sheet in which more of the active material having a smaller particle diameter is applied on the surface of the electrode mixture layer. 
     As described above in detail, in the manufacturing method of the electrode sheet  10  according to the present embodiment, the applying step and the heating-pressing step are performed. In the applying step, the electrode mixture material  40  is applied on the first surface  21  that is the surface of the current collector foil  20  on which the electrode mixture layer  30  is formed. In the heating-pressing step, the layer of the electrode mixture material  40  applied on the first surface  21  of the current collector foil  20  is pressed in its thickness direction while being heated. Further, as the applying step, the first applying step and the second applying step are performed. In the first applying step, the backup roll  120 A and the supply roll  130 A are used. The backup roll  120 A is rotated while being in contact with the second surface  22  of the current collector foil  20  so as to convey the current collector foil  20 . The supply roll  130 A is rotated while being supplied with the electrode mixture material  40  in a powder state on the surface of the supply roll  130 A. In addition, a potential difference is produced between the backup roll  120 A and the supply roll  130 A. Thereby, a potential difference is produced between the electrode mixture material  40  and the current collector foil  20 , and using an electrostatic force acting therebetween, the electrode mixture material  40  is moved from the surface of the supply roll  130 A to the first surface  21  of the current collector foil  20 . In this manner, in the first applying step, the electrode mixture material  40  is applied on the first surface  21  of the current collector foil  20 . The same applies to the second applying step performed after the first applying step. Thus, the electrode sheet  10  having the electrode mixture layer  30  with a sufficient thickness is efficiently manufactured. Accordingly, the electrode sheet manufacturing method capable of efficiently manufacturing a high-quality electrode sheet is realized. 
     Note that the present embodiment is merely exemplified and does not limit the present disclosure at all. Therefore, the present disclosure can naturally be improved and modified in various manners without departing from the gist thereof. For example, in the above embodiment, the description has been provided on the example in which the present disclosure is applied to a negative electrode of a lithium ion rechargeable battery. However, the present disclosure can also be applied to a positive electrode. For example, in the above embodiment, the description has been provided on the example in which the present disclosure is applied to an electrode sheet used as a negative electrode of a lithium ion rechargeable battery. However, the present disclosure can be applied not only to electrode sheets used for lithium ion rechargeable batteries but also to electrode sheets used for rechargeable batteries of other types. In the above description, the description has been provided on the example in which the active material and the binder are used as the electrode mixture material; however, for example, materials such as a conductive aiding material may be added as appropriate for the purpose of enhancing the conductivity in the electrode mixture layer. 
     Further, for example, in the above-described embodiment, it has been described that the heating-pressing step that pressing the layer of the electrode mixture material disposed on the current collector foil while heating this layer is performed by carrying out the heating and the pressing simultaneously using the pair of hot press rolls. However, for example, in the heating-pressing step, it may be configured to heat the layer of the electrode mixture material disposed on the current collector foil, and then press the heated layer of the electrode mixture material before the temperature of this heated layer is lowered to a temperature at which the binding action of the binder is not caused. 
     Moreover, for example, in the above-described embodiment, the description has been provided specifically on the manufacturing method of the electrode sheet having the electrode mixture layer on only one surface of the current collector foil. However, the electrode sheet may have the electrode mixture layers on both the front and back surfaces. When the electrode sheet having the electrode mixture layers on both sides of the current collector foil are manufactured, a set of the applying step and the heating-pressing step described in the above embodiment may be performed twice, respectively on the front side and the back side of the current collector foil.