JP6103250B2 - Method for manufacturing electrode for power storage device - Google Patents

Description

  The present invention relates to a method for manufacturing an electrode for a power storage device, and more particularly to a method for manufacturing an electrode for a power storage device characterized by a method for drying an active material mixture applied to a strip-shaped metal foil.

  Power storage devices such as secondary batteries and capacitors are widely used as power sources because they can be recharged and can be used repeatedly. For example, as a power storage device mounted on a vehicle such as an EV (Electric Vehicle) or a PHV (Plug-in Hybrid Vehicle), a lithium ion secondary battery, a nickel hydride secondary battery, or the like is well known. The power storage device includes a sheet-like positive electrode and a sheet-like negative electrode each having an active material layer formed by applying a slurry-like or paste-like active material mixture containing an active material to a metal foil. The electrode assembly is laminated or wound so as to form a layer in the presence of the.

  In the electrode manufacturing process, after the application process of applying the active material mixture to the strip-shaped metal foil is performed, the drying process of heating and drying the active material mixture is performed. In the coating process, the strip-shaped metal foil is fed from the supply reel and wound on the winding reel, and the active material mixture is applied to the metal foil during the transport. In the drying step, the metal foil wound on the take-up reel is accommodated in the drying device together with the take-up reel and heated and dried together with the take-up reel.

  Among power storage devices, in non-aqueous power storage devices such as lithium ion secondary batteries and lithium ion capacitors, moisture remaining in the active material layer deteriorates the performance of the power storage device. It is necessary to make it below a predetermined amount.

  Conventionally, a step of attaching an active material to an electrode material, a step of drying an electrode material to which the active material is attached (referred to as an electrode for convenience), a step of deriving a weight reduction rate of the electrode during the drying step, and deriving An electrode manufacturing method has been proposed that includes a step of ending the drying step based on the weight reduction rate (see Patent Document 1). In the method of Patent Document 1, when the amount of moisture contained in the electrode changes, the amount of evaporation of the moisture per unit time changes. When the electrode contains a lot of moisture, the amount of evaporation per unit time increases. Thus, the inventors have paid attention to the fact that the amount of evaporation per unit time decreases when the electrode does not contain much water. Then, when the drying of the electrode is terminated when the weight reduction rate corresponding to a predetermined amount of water is reached, an electrode containing the predetermined amount of water can be manufactured.

JP 2007-122889 A

  However, the inventor of the present application has an active material layer of a strip-shaped metal foil (hereinafter sometimes simply referred to as a strip-shaped electrode) coated with an active material mixture wound around a winding reel after the drying step. The amount of moisture contained in is not constant in the thickness direction of the wound layer of the strip electrode wound on the take-up reel, but is large at the center in the thickness direction and small at the outer end in the thickness direction. I found it. And it has also been found that the moisture content at the central portion in the thickness direction increases as the thickness of the wound layer increases. Therefore, in the method of Patent Document 1, depending on the thickness of the winding layer of the strip electrode wound on the winding reel, the water content in the central portion in the thickness direction of the winding layer is larger than the target amount. Become.

  The present invention has been made in view of the above-described problems, and its object is to provide a predetermined amount that prevents and suppresses the amount of water contained in the active material layer of the strip-shaped electrode after drying from deteriorating the performance of the power storage device. It is providing the manufacturing method of the electrode for electrical storage apparatuses which can be made below.

A method for manufacturing an electrode for a power storage device that solves the above problems includes an application step of applying an active material mixture to at least one surface of a strip-shaped metal foil, and winding the strip-shaped metal foil coated with the active material mixture. A winding step of winding on a reel, and a drying step of drying the active material mixture applied to the strip-shaped metal foil in a state where the metal foil is wound on the winding reel. A method for manufacturing an electrode for a power storage device, wherein the length of the strip-shaped metal foil wound around the winding reel in the winding step is the length of the metal foil wound around the winding reel. The thickness of the layer is set to 75 mm or less, and in the drying step, the active material mixture is dried without providing a heater at the core of the winding reel, and after the drying step, Metal foil wound on a take-up reel Residual water content in the middle of the thickness direction of at 20ppm or less, and was the residual water content in the center than twice the residual water content in the end portion in the thickness direction of the metal foil layer.

  After the completion of the drying process of the metal foil layer wound on the take-up reel, the residual moisture content at the center in the thickness direction of the metal foil layer is larger than the amount at the outer edge in the thickness direction of the metal foil layer. Become. In a power storage device having a layered structure in which a positive electrode and a negative electrode are insulated, uneven distribution of residual moisture is not preferable between the positive electrodes of the layers or the negative electrodes of the layers. In particular, in the case of a lithium ion secondary battery, since the residual water amount affects the lithium precipitation, the uneven distribution of the residual water amount is less preferable, and the difference in the residual water amount between the layers is preferably twice or less. Therefore, according to the configuration of the present invention, the moisture content contained in the active material layer of the strip electrode after drying is reduced at any position of the metal foil wound up on the winding reel. It is possible to make the amount below a predetermined amount that prevents and suppresses the above.

Further , after the drying process, the amount of water contained in the active material layer of the strip-shaped electrode after drying is less than or equal to a predetermined amount that suppresses and prevents a decrease in performance of the power storage device in an electrode having a general active material layer. Become. In addition, in the case of a lithium ion secondary battery, it is known that the charge / discharge cycle can be improved up to about 4000 cycles when the residual moisture content of the electrode is 20 ppm or less, so that the life of the power storage device can be extended. it can.

  According to the present invention, the amount of water contained in the active material layer of the strip-shaped electrode after drying can be made equal to or less than a predetermined amount that suppresses and prevents a decrease in performance of the power storage device.

The side view which shows typically the application | coating method of the active material mixture with respect to metal foil. The schematic cross section of the reel for winding cut | disconnected by the surface containing the center of a core part. The schematic diagram which shows the punching position of the electrode for lamination | stacking from a strip | belt-shaped electrode. The schematic diagram which shows the relationship between the outer diameter of a core part, and the thickness of the wound strip | belt-shaped electrode layer. The schematic diagram of the strip | belt-shaped electrode of another embodiment. The schematic diagram of the strip | belt-shaped electrode of another embodiment.

Hereinafter, one embodiment embodied in the manufacturing method of the strip electrode used for manufacture of the electrode for multilayer electrode assemblies is described according to FIGS.
The manufacturing method of the strip electrode includes an application step of applying an active material mixture on at least one surface of the strip metal foil, and a winding step of winding the strip metal foil coated with the active material mixture around a winding reel. And a drying step in which the active material mixture applied to the band-shaped metal foil is dried in a state where the metal foil is wound around the winding reel.

  As shown in FIG. 1, in the coating process, the active material mixture S is applied to the strip-shaped metal foil 12 fed out from the supply reel 11 by the coating device 20, and in the winding process, the active material mixture S is applied. After the dried metal foil 12 is dried by the drying device 22, the metal foil 12 is taken up on a take-up reel 26.

  The coating apparatus 20 includes a tank 20a for storing the slurry-like active material mixture S, a coating roll 20b, and a comma roll 20c that adjusts the thickness (amount) of the active material mixture S. In addition, the coating apparatus 20 includes a back roll (backing roll) 20 d that transfers the metal foil 12. The back roll 20d is disposed in the vicinity of the front of the coating roll 20b and is brought into contact with the coating roll 20b with the strip-shaped metal foil 12 that is fed from the supply reel 11 and passes between the coating roll 20b and the back roll 20d. (Position shown in FIG. 1) and a separating position for separating the metal foil 12 from the coating roll 20b by a moving means (not shown).

  The coating roll 20b and the back roll 20d are always rotated clockwise in FIG. 1 during operation. When the back roll 20d is disposed at the contact position, the active material mixture S supplied onto the coating roll 20b is transferred onto the metal foil 12, and when the back roll 20d is disposed at the separated position, the coating roll 20b is disposed. The active material mixture S supplied to the metal foil 12 is not transferred onto the metal foil 12. In this embodiment, since the strip electrode is used for manufacturing the electrode for the laminated electrode assembly, the active material mixture S is formed on the metal foil 12 by arranging the back roll 20d at the spaced position at predetermined intervals. Is intermittently applied at a predetermined length. A dancer roll 28 is provided between the supply reel 11 and the back roll 20d, and between the drying device 22 and the take-up reel 26, and the dancer roll 28 adjusts the tension of the metal foil 12 to be transferred. Adjust to prevent sagging of the metal foil 12.

  The coating device 20 is configured to apply the active material mixture S to one surface of the metal foil 12 supplied from the supply reel 11, and when applying the active material mixture S to both surfaces of the metal foil 12, The reel 26 for winding around which the metal foil 12 coated with the active material mixture S is wound on one surface is used as the supply reel 11, and the metal foil 12 is fed out from the supply reel 11 to the other surface. The active material mixture S is applied.

  The metal foil 12 coated with the active material mixture S is roll-pressed by a press roller, and the active material mixture S is compressed to form an active material layer 13 (shown in FIG. 3). When the active material layer 13 is formed on both surfaces of the metal foil 12, the metal foil 12 coated with the active material mixture S on both surfaces of the metal foil 12 and wound around the take-up reel 26 is rolled by a press roller. The metal foil 12 in which the active material layer 13 is formed on both sides by pressing is obtained.

  The supply reel 11 and the take-up reel 26 are driven in a state where the shaft of the drive mechanism is fitted and inserted into the core portion. However, since the diameter of the shaft is generally small, if the core portion is made into a simple cylindrical shape, When the metal foil 12 wound around the take-up reel 26 is unwound, curling (warping) occurs.

  As shown in FIG. 2, the take-up reel 26 surrounds the cylindrical inner cylinder 26b, the inner cylinder 26b, and the inner cylinder 26b between a pair of annular side plates 26a in order to suppress the occurrence of curling. A core portion having a concentric cylindrical outer cylinder 26c is formed in a double tubular shape. A shaft of a winding mechanism (not shown) can be fitted into the inner cylinder 26b. The strip electrode 15 in which the active material layer 13 is intermittently formed on the metal foil 12 is wound around the outer peripheral surface of the outer cylinder 26c in a state having a gap with the side plate 26a. The outer diameter of the outer cylinder 26c is such that when the metal foil 12 wound around the outer cylinder 26c is unwound, the size of the curl (warp) generated in the metal foil 12 is formed from a strip electrode. In order to stack the three-dimensional electrodes with high accuracy, the electrodes are formed in a size that does not hinder.

  As shown in FIG. 3, the tabs 17 a of the electrode assembly electrode 17 project along the longitudinal direction of the electrode strip 15 so that the electrode assembly electrode 17 is indicated by a two-dot chain line from the electrode strip 15. When the outer cylinder 26c is formed by punching into a shape to be formed, the outer diameter of the outer cylinder 26c is preferably 250 mm or more.

  The active material mixture S applied to the metal foil 12 is dried by the drying device 22. This drying is performed to the extent that the active material mixture S can be pressed without any problem. For this reason, a high boiling point solvent used as a solvent for the positive electrode active material mixture S, for example, NMP (N methylpyrrolidone) still remains in the active material mixture S, and NMP easily absorbs moisture. Due to the solvent, moisture remains in the active material mixture S. Therefore, the metal foil 12 coated with the active material mixture S is heat-dried by a heat-drying device while being wound around the take-up reel 26. Heating and drying is performed in a reduced pressure state (vacuum state).

  When the metal foil 12 coated with the active material mixture S (hereinafter, appropriately referred to as a strip electrode 15) is heated and dried by a heating and drying apparatus in a state of being wound around the winding reel 26, it is used for winding. When the thickness of the layer of the strip electrode 15 wound around the reel 26 is large, the residual moisture content of the strip electrode 15 is different between the central portion and the end portion in the thickness direction of the strip electrode layer. Specifically, when the thickness is 75 mm, the residual water content at the center is about twice that at the end, and when the thickness is 175 mm, the residual water content at the center is about four times that at the end. This is because, in the drying process, the heat history is different between the central portion in the thickness direction of the belt-like electrode layer wound on the take-up reel 26 and the end portion, and when the thickness is large, the dry state is different. it is conceivable that.

  Therefore, the length of the metal foil 12 coated with the active material mixture S that is wound in the winding process is the thickness of the metal foil layer that is wound on the winding reel 26 after the drying process is finished. The residual moisture content at the center in the direction is set to be equal to or less than a preset amount, and the residual moisture content at the center is set to be equal to or less than twice the residual moisture content at the end in the thickness direction of the metal foil layer. The length of the metal foil 12 varies depending on the material and thickness of the metal foil 12 to be used, the thickness of the active material layer 13, and the type of the active material. For example, when the diameter of the outer cylinder 26c of the take-up reel 26 is 250 mm, the strip electrode 15 wound around the take-up reel 26, that is, the metal foil layer of the metal foil 12 coated with the active material mixture S is used. The thickness is set to 75 mm or less.

  As shown in FIG. 4, when the outer diameter of the outer cylinder 26c is d and the thickness of the layer of the strip electrode 15 wound on the outer cylinder 26c is A, the band electrode 15 is wound with d + A up to 200 mm. In the case where d + A is wound up to 300 mm, the residual moisture amount per unit weight at the inner end portion, the central portion, and the outer end portion in the thickness direction of the layer of the strip electrode 15 is obtained after heating and drying at 120 ° C. for 6 hours. It was measured.

  As the strip electrode 15, a positive electrode having a metal foil 12 thickness of 15 μm and an active material layer 13 thickness of 120 μm was used, and moisture measurement was performed by the Karl Fischer method. The results when the strip electrode 15 is wound up to 200 mm with d + A are shown in Table 1, and the results when it is rolled up to 300 mm with d + A are shown in Table 2.

From Table 1 and Table 2, it is confirmed that the amount of residual moisture is different between the central portion and the end portion in the thickness direction, and is large at the central portion in the thickness direction and small at the outer end in the thickness direction. Further, it is confirmed that the amount of residual moisture in the central portion increases as the amount of winding (winding thickness) around the winding reel 26 increases. When d + A was 200 mm, the residual water content at the center was 20 ppm, and when d + A was 300 mm, the residual water content at the center was 50 ppm.

  In a power storage device having a layered structure in which a positive electrode and a negative electrode are insulated, uneven distribution of residual moisture is not preferable between the positive electrodes of the layers or the negative electrodes of the layers. In particular, in the case of a lithium ion secondary battery, since the residual water amount affects the lithium precipitation, the uneven distribution of the residual water amount is less preferable, and the difference in the residual water amount between the layers is preferably twice or less.

  In the case of Table 1, the residual moisture content of the strip electrode 15 is less than twice the difference between the central portion where the moisture amount is large and the outer end portion where the moisture amount is small. When the positive electrode is manufactured, the difference in the residual water content of each layer of the positive electrode constituting the electrode assembly using the positive electrode is twice or less.

  In the case of a lithium ion secondary battery, it is known that the charge / discharge cycle can be improved to about 4000 cycles when the residual moisture content of the electrode is 20 ppm or less. When d + A is 200 mm or less, that is, A is 75 mm or less, when a positive electrode for a stacked electrode assembly is manufactured from the strip electrode 15, the residual moisture content of the positive electrode of the power storage device including the stacked electrode assembly is It becomes 20 ppm or less, and it becomes possible to improve a charging / discharging cycle to about 4000 cycles, and can extend the lifetime of an electrical storage apparatus.

  On the other hand, in the case of Table 2, the residual water content of the strip electrode 15 is four times or more the difference between the central portion where the water content is high and the outer end portion where the water content is low. When a positive electrode for a laminated electrode assembly is manufactured from the strip electrode 15, the difference in the residual water content of each positive electrode is not doubled or less and is rejected.

  In the case where the strip electrode 15 is wound to d + A up to 300 mm, if the time of the drying process is lengthened, it is possible to reduce the residual water content in the central portion to 20 ppm or less. However, in this case, the drying process takes a long time, and not only the productivity is lowered, but also the portion of the strip electrode 15 existing at the end in the thickness direction wound around the take-up reel 26 is unnecessary. It will be subjected to heating for a long time, which is not preferable.

  For the strip electrode 15 manufactured using an active material having the same active material type and a smaller particle size distribution, heating the strip electrode 15 at 120 ° C. for 6 hours when d + A is wound up to 200 mm After drying, the residual water content per unit weight at the inner end portion, the central portion, and the outer end portion in the thickness direction of the layer of the strip electrode 15 was measured. The results are shown in Table 3.

From Table 3, it is confirmed that the residual moisture amount is different between the central portion and the end portion in the thickness direction, and is large at the central portion in the thickness direction and small at the outer end in the thickness direction. Moreover, unlike Example 1, the residual moisture content was the same as the central portion in the thickness direction at the inner end in the thickness direction. The take-up reel 26 was the same as that used in Example 1. Compared to the case of Table 1 of Example 1 where d + A is the same as 200 mm, it is the same in the central portion in the thickness direction and less at the outer end in the thickness direction, but at the inner end in the thickness direction. Residual water content became the same as the central part. Moreover, the amount of residual moisture was larger in Example 2 (Table 3) at both the central portion and the outer end. As the cause, in Example 2, the particle size distribution of the active material used is shifted to a smaller one, and the measurement variation is considered.

  In this Example 2, the difference between the portion having a large amount of residual water (center portion) and the portion having a small amount of water (outer end) is small (about 20%). When the positive electrode is manufactured, the difference in the residual water content of each positive electrode becomes smaller than that in Example 1, which is preferable.

  If the moisture content of the positive electrode is 50 ppm or less and the difference in moisture content of each positive electrode of the electrode assembly using the positive electrode is twice or less, the power storage device equipped with the electrode assembly suppresses the performance degradation of the power storage device. It becomes possible to prevent.

According to this embodiment, the following effects can be obtained.
(1) A method for manufacturing an electrode for a power storage device includes a coating step of applying an active material mixture S to at least one surface of a strip-shaped metal foil 12, and winding the strip-shaped metal foil 12 coated with the active material mixture S. A winding step for winding the material on the reel 26 and a drying step for drying the active material mixture S applied to the belt-shaped metal foil 12 in a state where the metal foil 12 is wound on the winding reel 26. ing. The length of the strip-shaped metal foil 12 taken up on the take-up reel 26 in the take-up process is the center in the thickness direction of the metal foil layer in the state taken up on the take-up reel 26 after the drying process. The residual moisture content in the film was set to be equal to or less than a preset amount, and the residual moisture content in the center was set to be twice or less the residual moisture content at the end in the thickness direction of the metal foil layer. Therefore, the amount of water contained in the active material layer 13 of the strip electrode 15 after drying can be made equal to or less than a predetermined amount that suppresses and prevents a decrease in performance of the power storage device.

  (2) The residual moisture content at the center in the thickness direction of the metal foil layer wound on the winding reel 26 is 50 ppm or less. According to this configuration, after the drying process is finished, the amount of water contained in the active material layer of the strip electrode after drying suppresses and prevents a decrease in performance of the power storage device in the positive electrode having a general active material layer. Less than a predetermined amount. In addition, for example, when a positive electrode for a laminated electrode assembly is manufactured from the obtained strip-shaped electrode, the variation in the amount of water between the positive electrodes is reduced, and lithium deposition occurs when the power storage device is a lithium ion secondary battery. It becomes difficult to have an adverse effect.

  (3) The residual moisture content at the center in the thickness direction of the metal foil layer in the state wound on the winding reel 26 is 20 ppm or less. Therefore, after the drying process is finished, the amount of water contained in the active material layer 13 of the strip-shaped electrode 15 after drying is a predetermined amount that suppresses and prevents a decrease in performance of the power storage device in an electrode having a general active material layer. It becomes the following.

  (4) The strip electrode 15 is used for manufacturing the electrode 17 for the laminated electrode assembly, and the outer diameter (diameter) of the outer cylinder 26c of the take-up reel 26 is 250 mm or more. Therefore, when the laminated electrode assembly electrode 17 is formed from the belt-like electrode 15, the laminated electrode assembly electrode 17 can be accurately laminated.

The embodiment is not limited to the above, and may be embodied as follows, for example.
As shown in FIG. 5, the strip electrode 15 has the active material mixture S intermittently at intervals suitable for punching the tab 17 a into a shape projecting in a direction perpendicular to the longitudinal direction of the strip electrode 15. An applied configuration may be used.

  As shown in FIG. 6, the strip electrode 15 is capable of forming a tab 17 a on the active material mixture S continuously along the longitudinal direction of the strip electrode 15 and at least on one end side in the width direction of the strip electrode 15. The structure applied so that the active material mixture non-application part 16 exists in width may be sufficient. The strip electrode 15 is not limited to the production of the electrode 17 for the laminated electrode assembly, but is a wound electrode assembly electrode in which a strip-like positive electrode and a negative electrode are wound in a laminated state with a separator interposed therebetween. By cutting into lengths, it can be used for the production of a wound electrode assembly electrode.

  (Circle) although the above-mentioned Example described about the positive electrode, you may apply this manufacturing method to a negative electrode. When an aqueous solvent is used for the active material mixture applied to the negative electrode, the amount of water remaining after the drying step is larger than in the case of the positive electrode, but the thickness of the wound layer of the strip electrode is the same as in the case of the positive electrode. This manufacturing method can be effectively applied because of the influence.

  ○ A two-strand manufacturing method for forming two strip electrodes by cutting one strip electrode 15 wound around the winding reel 26 after the drying process along its longitudinal direction. You may apply to. Moreover, you may apply to the manufacturing method which cut | disconnects the strip | belt-shaped electrode 15 of 1 sheet along the longitudinal direction, and forms 3 or more strip | belt-shaped electrodes.

  ○ The manufacturing method of the strip electrode 15 in which the active material mixture S is applied on both surfaces of the metal foil 12 is a winding reel 26 in which the strip electrode 15 in which the active material mixture S is applied on one surface is wound. Is not limited to the configuration in which the active material mixture S is applied to the other surface of the metal foil 12 by using as the supply reel 11. For example, two coating devices that discharge and apply the slurry-like active material mixture S from the die head are provided so as to sandwich the metal foil 12, and the active material mixture S is applied to both surfaces of the metal foil 12. It is good also as a structure.

  The strip electrode 15 is not limited to the configuration in which the active material mixture S is applied to both surfaces of the metal foil 12 and the active material layer 13 is formed, but the active material mixture S is applied to one surface of the metal foil 12 and active. The structure in which the material layer 13 was formed may be sufficient. When the active material layer 13 is formed only on one side of the metal foil 12, a press roller is provided on the downstream side in the transport direction of the metal foil 12 of the drying device 22, and the metal foil 12 on the metal foil 12 dried by passing through the drying device 22 is provided. After the active material mixture S is pressed, the active material mixture S may be wound around the winding reel 26.

  The strip electrode 15 is not limited to a lithium ion secondary battery or a lithium ion capacitor as a non-aqueous power storage device, and may be applied to, for example, a magnesium secondary battery.

  S ... Active material mixture, 12 ... Metal foil, 26 ... Reel for winding.

Claims (1)

An application step of applying an active material mixture to at least one surface of the strip-shaped metal foil; a winding step of winding the strip-shaped metal foil coated with the active material mixture around a winding reel; and the strip-shaped metal A method for producing an electrode for a power storage device comprising a drying step in which the active material mixture applied to the foil is dried in a state where the metal foil is wound on the winding reel,
The length of the strip-shaped metal foil wound on the winding reel in the winding step is set so that the thickness of the metal foil layer in the state wound on the winding reel is 75 mm or less. In the drying step, the active material mixture is dried without providing a heater at the core of the winding reel, and after the drying step, the winding material is wound on the winding reel. characterized in that the residual water content in the middle of the thickness direction of the metal foil layer is in 20ppm or less, and was the residual water content in the center than twice the residual water content in the end portion in the thickness direction of the metal foil layer A method for manufacturing an electrode for a power storage device.