JP2013026444A - Method for manufacturing electrode for nonaqueous electrolyte electrochemical element, and nonaqueous electrolyte electrochemical element with electrode for nonaqueous electrolyte electrochemical element thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode for a nonaqueous electrolyte electrochemical element capable of suppressing occurrence of a binder density difference in a thickness direction, and to provide a nonaqueous electrolyte electrochemical element with an electrode for a nonaqueous electrolyte electrochemical element thereof.SOLUTION: A method for manufacturing a positive electrode with thickness of 0.3 mm or more includes: an application step of applying a slurry containing a positive electrode active material, a binder, and a solvent onto a collector; and a drying step of evaporating the solvent by a heating device. The drying step keeps a surface temperature of the applied body to which the slurry is applied at a temperature equal to or lower than a prescribed surface temperature.

Description

  The present invention relates to a method for producing a nonaqueous electrolyte electrochemical element electrode and a nonaqueous electrolyte electrochemical element including the nonaqueous electrolyte electrochemical element electrode.

  In recent years, more and more large-capacity power storage systems are required. For example, an electric power network called a smart grid has attracted attention. In order to realize a smart grid, a large-capacity power storage system that temporarily stores electric power is required. There is also a demand for a large-capacity power storage system for electric vehicles. As an emergency power source for various types of electrical equipment, it is required to increase the capacity of a power storage system.

  Examples of the power storage device of the power storage system include a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a molten salt battery represented by a sodium molten salt battery, and an electric double layer capacitor represented by a lithium ion capacitor. It is used. In addition, since the former two and the latter are largely different in charging principle, they are collectively referred to as an electrochemical element, and among them, an electrolyte that does not contain water in principle is a non-aqueous electrolyte. It is called a chemical element. Hereinafter, various nonaqueous electrolyte electrochemical elements will be briefly described.

In a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery (LIB), a lithium metal oxide is used for the positive electrode, carbon is used for the negative electrode, and an organic electrolyte is used for the electrolytic solution. As an example of the organic electrolyte, a solution in which LiPF ₆ as a supporting salt responsible for ionic conduction is dissolved in an organic solvent of EC (ethylene carbonate) -DEC (diethyl carbonate) mixed at a concentration of 1 mol / L can be mentioned. In addition, since the ionic conductivity of the organic electrolyte to be used is one digit or more lower than that of the aqueous electrolyte, it is necessary to ensure the ionic conductivity in the electrode active material layer (hereinafter referred to as the electrode layer). It is said. For this reason, the thickness of the electrode layer cannot basically be increased, and the thickness formed on one surface of the current collector is in the range of 100 μm to 300 μm (for example, Patent Document 1).

The molten salt battery has been attracting attention in recent years because it has higher ionic conductivity than a lithium ion secondary battery, easily obtains a high capacity and high output, and has developed a molten salt that melts at 200 ° C. or lower. As the molten salt, M ^{n +} [N ⁻ (SO ₂ R ¹ R ² ) ₂ ] _n (M: one kind of alkali metal or alkaline earth metal, n: an integer of 1 or 2 in terms of valence, R ¹ , R ² ; independently a fluorine or fluoroalkyl group) or a mixture thereof (see Patent Document 2).

A lithium ion capacitor (LIC) stores electricity by forming an electric double layer on a positive electrode and a negative electrode. As the positive electrode, an electrode in which activated carbon is filled in an aluminum current collector is used. As the negative electrode, an electrode in which a copper current collector is filled with a negative electrode active material capable of inserting and extracting lithium ions such as graphite powder is used. As the electrolytic solution, for example, an organic solvent in which a lithium salt such as LiPF ₆ and EC-DEC are mixed is used (for example, Patent Document 3).

  As described above, three types of non-aqueous electrolyte electrochemical elements are listed as the power storage device of the power storage system. However, regardless of the battery structure, a large capacity is required for each. In order to realize a large capacity, it is necessary to increase the capacity of an electrode that absorbs and releases an active material or an electrode that absorbs and desorbs an active material. That is, it is necessary to increase the electrode thickness.

  Since the lithium ion secondary battery (LIB) has low ionic conductivity, the thickness of the positive electrode formed on one surface of the current collector is currently in the range of 100 μm to 300 μm, but does not require a high discharge rate. In applications, lithium ion secondary batteries with increased capacity are required. Specifically, the positive electrode thickness is required to be 300 μm or more.

  Since the molten salt battery has high ionic conductivity, the thickness of the electrode layer can be 300 μm or more. For this reason, a battery with a capacity higher than that of the lithium ion secondary battery can be configured. However, in applications such as vehicles, higher capacity is required. Specifically, a positive electrode having a thickness of 0.3 mm or more is required.

  The same applies to lithium ion capacitors, and in order to increase the capacity, it is required to increase the thickness of the positive electrode and the negative electrode. In particular, in the conventional lithium ion capacitor, since the negative electrode capacity is larger than the positive electrode capacity, the capacity of the lithium ion capacitor is determined by the positive electrode capacity. For this reason, in order to further increase the capacity of the lithium ion capacitor, a positive electrode having a thickness of 0.3 mm or more is required.

  By the way, the electrodes of these non-aqueous electrolyte electrochemical elements are formed by the same manufacturing method. That is, the positive electrode of the non-aqueous electrolyte secondary battery, the positive electrode of the molten salt battery, the positive electrode or the negative electrode of the electric double layer capacitor are mixed with the active material and the resin solvent of the binder to form a slurry. The current collector is formed by coating or filling the current collector, drying it, and further heat-treating it. In addition, the last heat processing may be abbreviate | omitted (refer patent document 1, patent document 3, and patent document 4).

Japanese Patent Laid-Open No. 08-096800 JP 2009-066764 A JP 2006-286919 A JP 2004-172035 A

  However, since this type of manufacturing method has the following problems, it has been difficult to form an electrode having a thickness of 0.3 mm or more and capable of securing a charging capacity. That is, in the above manufacturing method, the slurry is dried at a comparatively high temperature in order to completely dry the inside of the electrode. However, if the temperature of the warm air is increased too much, the surface of the coated body obtained by applying slurry to the current collector is dried before the inside. As a result of this drying, the surface temperature rises, the binders on the surface adhere to each other, and a binder layer is formed on the surface. For this reason, it becomes difficult for the internal solvent to evaporate. If the drying is further performed in a state where the surface is dry, the movement of the binder occurs as the solvent evaporates, the density of the binder on the surface increases, and the density of the internal binder decreases. As a result, there is no sufficient amount of binder to fix the active material to the current collector in the coated body, and the active material and the current collector are separated from each other. And no longer contributes to the discharge.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for producing an electrode for a non-aqueous electrolyte electrochemical device capable of suppressing the occurrence of a binder density difference in the thickness direction and the non-use thereof. It is providing the nonaqueous electrolyte electrochemical element provided with the electrode for water electrolyte electrochemical elements.

Hereinafter, means for achieving the above object will be described.
(1) The invention described in claim 1 is a method for manufacturing an electrode for a non-aqueous electrolyte electrochemical device having a thickness of 0.3 mm or more, and a slurry containing an active material, a binder, and a solvent is applied to a current collector And a drying step of evaporating the solvent by a heating device, and the gist of the drying step is to maintain the surface temperature of the coated body to which the slurry has been applied below a set surface temperature.

  According to this configuration, since the surface temperature of the application body is maintained below the set surface temperature, the surface of the application body can be prevented from drying earlier than the inside of the application body. Moreover, it can suppress that the binder in the surface adhere | attaches and that a binder layer is formed in the surface. As a result, since the amount of the solvent accumulated in the inside of the coated body is reduced, the increase in the binder density difference between the surface and the inside of the nonaqueous electrolyte electrochemical element electrode is suppressed.

  (2) The invention according to claim 2 is the method for producing an electrode for a non-aqueous electrolyte electrochemical element according to claim 1, wherein, in the drying step, the surface temperature of the coated body is maintained below a set surface temperature. In addition, the gist is to maintain the absolute value of the temperature difference between the surface temperature and the internal temperature of the coated body coated with the slurry within a set temperature range.

  According to this structure, it is suppressed that a difference arises between the drying degree in the inside of an application body, and the drying degree in the surface of an application body. That is, the surface of the coated body is prevented from drying before the inside, and the amount of the binder that moves from the inside to the surface is reduced, so that the binder density difference between the surface and the inside in the thickness direction of the coated body is reduced. Can be small.

(3) The invention according to claim 3 is summarized in that, in the method for producing an electrode for a nonaqueous electrolyte electrochemical element according to claim 2, the set temperature width is 50 ° C.
According to this configuration, the binder density difference between the surface and the inside can be reduced as compared with the case of drying under the condition that the temperature difference between the surface and the inside of the coated body is greater than 50 ° C.

  (4) The invention according to claim 4 is the method for producing an electrode for a non-aqueous electrolyte electrochemical element according to any one of claims 1 to 3, wherein the set surface temperature is 150 ° C. And

  According to this configuration, the binder layer is formed on the surface of the coated body or the thickness of the layer is larger than that when the surface temperature of the coated body is dried under a condition that allows the surface temperature to exceed 150 ° C. It can be suppressed.

  (5) The invention according to claim 5 is the method for producing an electrode for a non-aqueous electrolyte electrochemical device according to any one of claims 1 to 4, wherein an infrared heating device having a wavelength of 2 μm to 4 μm is used as the heating device. The gist is to use.

  Since infrared rays are transmitted to the inside of the application body, the temperature difference between the surface temperature of the application body and the internal temperature can be reduced as compared with the case of heating with warm air. For this reason, it is suppressed that the surface of an application body dries earlier than the inside of an application body. In particular, in the case of a medium wavelength infrared ray having a wavelength of 2 μm to 4 μm, it has the following characteristics as compared with a long wavelength infrared ray and a short wavelength infrared ray. Therefore, it is preferable to use a medium wavelength infrared ray among the infrared rays for drying the coated body.

  In the case of long-wavelength infrared (wavelength greater than 4 μm), it hardly penetrates to the inside of the coated body. For this reason, the surface of the application body is heated faster than the inside. On the other hand, the medium wavelength infrared light is transmitted to the inside of the coated body. For this reason, the temperature difference between the surface and the inside of the coated body can be reduced as compared with the case where heating is performed using long-wavelength infrared rays, and thereby the degree of drying inside the coated body and the degree of drying on the surface of the coated body. It can suppress that a difference arises between.

  In the case of short wavelength infrared rays (0.78 μm to less than 2 μm), it passes through the inside of the coated body, but since the amount of light absorbed by the transmissive body is small, the coated body cannot be heated efficiently and the drying time is short. become longer. On the other hand, medium wavelength infrared rays have a larger amount of light absorbed by the coated body than short wavelength infrared rays. For this reason, compared with the case where it heats using short wavelength infrared rays, an application body can be heated in a short time.

  (6) The invention according to claim 6 is characterized in that, in the method for producing an electrode for a non-aqueous electrolyte electrochemical element according to any one of claims 1 to 5, an induction heating device is used as the heating device. .

According to this configuration, the current collector can be heated uniformly. Thereby, it can suppress that the surface of an application body dries earlier than the inside of an application body.
(7) The invention according to claim 7 is a non-aqueous electrolyte electrochemical element comprising an electrode manufactured by the method for manufacturing an electrode for non-aqueous electrolyte electrochemical element according to any one of claims 1 to 6.

  According to this configuration, since the electrode is manufactured by the above-described method for manufacturing an electrode for a non-aqueous electrolyte electrochemical element, a difference in binder density between the surface and the inside of the electrode is reduced. That is, since the binder layer is not formed on the surface of the electrode or the layer is thin, the increase in internal resistance due to the binder layer is small. Compared to a battery including an electrode manufactured by a conventional manufacturing method, the charge / discharge capacity of the electrochemical element can be increased.

  (8) The invention according to claim 8 includes a positive electrode produced by the method for producing an electrode for a non-aqueous electrolyte electrochemical device according to any one of claims 1 to 6, wherein the electrolyte is a molten salt. It is an electrolyte electrochemical element, that is, a molten salt battery.

  According to this configuration, since the positive electrode is manufactured by the above-described method for manufacturing an electrode for a non-aqueous electrolyte electrochemical device, the binder density difference between the surface and the inside of the positive electrode is reduced. That is, since the binder layer is not formed on the surface of the positive electrode or the layer is thin, the increase in internal resistance due to the binder layer is small. Compared to a battery including a positive electrode manufactured by a conventional manufacturing method, the charge capacity of the battery can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements which can suppress that a binder density difference arises in thickness direction, and the nonaqueous electrolyte electricity provided with the electrode for nonaqueous electrolyte electrochemical elements A chemical element can be provided.

The schematic diagram which shows typically the molten salt battery of 1st Embodiment of this invention. The flowchart which shows the manufacturing process of a positive electrode about the molten salt battery of the embodiment. The schematic diagram which shows typically the infrared heating apparatus used for manufacture of the positive electrode of the embodiment. The schematic diagram which shows typically the induction heating apparatus used for manufacture of the positive electrode of the embodiment.

<First Embodiment>
An example of a non-aqueous electrolyte electrochemical element is a sodium molten salt battery. Hereinafter, an example of the embodiment will be described.

  As shown in FIG. 1, the molten salt battery 1 includes a positive electrode 10, a negative electrode 20, a separator 30 disposed between the positive electrode 10 and the negative electrode 20, and a storage case that stores the positive electrode 10, the negative electrode 20, and the separator 30. 40. The housing case 40 is filled with molten salt.

  The housing case 40 includes a positive electrode case 41 electrically connected to the positive electrode 10, a negative electrode case 42 electrically connected to the negative electrode 20, and a sealing member that seals between the positive electrode case 41 and the negative electrode case 42. 43 and a leaf spring 44 that presses the negative electrode 20 toward the positive electrode 10.

  The positive electrode case 41 functions as a positive electrode terminal of the battery. The negative electrode case 42 functions as a negative electrode terminal of the battery. The sealing member 43 is formed of a positive electrode active material, a negative electrode active material, and a fluorine-based elastic member that is not corroded by molten salt. The positive electrode case 41 and the negative electrode case 42 are formed of a conductive member that does not corrode due to an oxidation-reduction reaction caused by charging / discharging of the molten salt battery 1, for example, an aluminum alloy.

  The positive electrode 10 includes a current collector 11 that collects electrons generated by a redox reaction of the positive electrode active material, a positive electrode active material, a binder, and a conductive additive. The positive electrode active material and the conductive additive are bonded to the current collector 11 with a binder. Electrons or holes generated in the positive electrode active material are transmitted to the current collector 11 through the conductive assistant.

  An aluminum nonwoven fabric is used as the current collector 11. The aluminum nonwoven fabric is in contact with the positive electrode case 41. An aluminum nonwoven fabric is an aggregate of aluminum fine wires. An aluminum oxide thin film is formed on the surface of the aluminum thin wire. As the current collector 11, for example, an aluminum nonwoven fabric having an average diameter of aluminum fine wires of 100 μm, a thickness of 100 μm to 1000 μm, and a porosity of 70% to 90% is used.

  An aluminum porous body can also be used as the current collector 11. An aluminum porous body is manufactured by forming an aluminum layer on a resin porous body having continuous pores (continuous vent holes) such as polyurethane by plating or vapor deposition, and then removing the underlying polyurethane by thermal decomposition or the like. be able to. The porosity is preferably 80% to 98%, and the pore diameter is preferably 50 μm to 500 μm.

As the positive electrode active material, an oxide that absorbs and releases sodium ions, for example, NaCrO ₂ is used. As the conductive assistant, a carbon-based conductive material that has conductivity and does not electrolyze, for example, acetylene black is used. As the binder, a substance that is inert to the electrolytic solution and adheres to aluminum or the like, for example, polyvinylidene fluoride is used.

As the molten salt, for example, a salt containing an anion (hereinafter referred to as “FSA”) represented by N (SO ₂ R1) (SO ₂ R2), a sodium cation, and a potassium cation (hereinafter, NaFSA-KFSA) is used. Here, R1 and R2 each represent F (fluorine). The composition ratio of NaFSA and KFSA is 56:44 in terms of molar ratio.

  An Sn—Na alloy is used as the negative electrode 20. The core part of the negative electrode 20 is Sn, and the surface is made of Sn—Na alloy. The Sn—Na alloy is formed by depositing Na on Sn metal by plating.

  The separator 30 isolates both electrodes so that the positive electrode 10 and the negative electrode 20 do not contact each other, and allows the molten salt to pass therethrough. The molten salt contacts the positive electrode 10 and the negative electrode 20. Specifically, a glass cloth having a thickness of 200 μm is used as the separator 30.

<Method for producing positive electrode>
With reference to FIG. 2, the manufacturing method of the positive electrode 10 is demonstrated.
NaCrO ₂ as a positive electrode active material, acetylene black as a conductive additive, polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone as a solvent in a mass ratio of 85: 10: 5: 50 Mix at a ratio to form a slurry (S100).

  Next, slurry is applied to the aluminum nonwoven fabric (application step: S110). Next, the slurry applied (hereinafter “applied body 50”) is dried by a heating device (drying step: S120). In the drying step, the heating device is controlled so that the surface temperature TA of the application body 50 is equal to or lower than the set surface temperature TSA. Thereafter, the dried application body 50 is pressed under a pressure of 1000 kgf / cm to a predetermined thickness (S130).

<Electrode manufacturing equipment>
With reference to FIG. 3, the electrode manufacturing apparatus 100 for manufacturing the positive electrode 10 is demonstrated.
The electrode manufacturing apparatus 100 performs a process from an application process for applying slurry to the sheet-like current collector 11 to a drying process for drying the application body 50.

  The electrode manufacturing apparatus 100 includes a transport unit 110 that transports the current collector 11, an application unit 120 that applies slurry to the current collector 11, a heating unit 130 that dries the application body 50, and a surface temperature of the application body 50. And a measuring unit 140 for measuring.

  The transport unit 110 includes a first transport roller 111 that feeds out the current collector 11 and a second transport roller 112 that winds up the current collector 11. The rotation speeds of the first conveyance roller 111 and the second conveyance roller 112 are controlled according to the degree of drying of the application body 50.

  The application unit 120 discharges slurry to the current collector 11 and smoothes the surface of the current collector 11. The coating amount per unit time is adjusted according to the conveyance speed of the current collector 11, the porosity of the current collector 11, the thickness of the current collector 11, and the like.

The measuring unit 140 is constituted by a surface temperature sensor.
A non-contact type sensor is employed as the surface temperature sensor. For example, a sensor that measures the surface temperature TA by absorbing the amount of infrared rays by an infrared absorption film and converting the infrared rays into heat and measuring the heat with a thermocouple is used. The value measured by the measuring unit 140 is corrected to the difference between the value and the actual surface temperature TA to obtain the measured surface temperature TAX. The measurement surface temperature TAX is output to the heating unit 130.

  The heating unit 130 includes an infrared heating device 200 that emits light having a wavelength of 2 μm to 4 μm (hereinafter, “medium wavelength infrared”). The infrared heating device 200 includes a medium wavelength infrared heater 210 having a wavelength of 2 μm to 4 μm, and a control unit 220 that selects a heater to be operated among the plurality of medium wavelength infrared heaters 210. The medium wavelength infrared heater 210 is disposed on the upper side and the lower side of the transport path of the current collector 11.

  The radiation intensity of the medium wavelength infrared heater 210 is set so that the surface temperature TA does not become abnormally higher than the internal temperature TB. Specifically, the condition that the absolute value of the temperature difference between the surface temperature TA of the application body 50 and the internal temperature TB of the intermediate portion in the thickness direction of the application body 50 is within the set temperature range TSC is satisfied. The radiation intensity of the wavelength infrared heater 210 is set. The radiation intensity of the medium wavelength infrared heater 210 is adjusted by the current flowing through the medium wavelength infrared heater 210. The set temperature range TSC is determined to be 50 ° C., for example.

  If the current flowing through the medium wavelength infrared heater 210 cannot be adjusted, the amount of light is adjusted by the following method. For example, the distance between the medium wavelength infrared heater 210 and the application body 50 is adjusted. Alternatively, a light amount cut filter (ND filter) or the like is disposed between the medium wavelength infrared heater 210 and the application body 50.

  The radiation intensity of the medium wavelength infrared heater 210 is obtained in advance by a test before the medium wavelength infrared heater 210 is dried. Specifically, a map showing the relationship between the amount of current flowing through the medium wavelength infrared heater 210, the surface temperature TA of the application body 50, the internal temperature TB of the application body 50, and the temperature difference is created. The range of the current amount of the infrared heater 210 is set.

  The controller 220 selects a heater to be operated from the plurality of medium wavelength infrared heaters 210 based on whether or not the measured surface temperature TAX of the surface temperature sensor exceeds the first set surface temperature TSA (set surface temperature). For example, when the measured surface temperature TAX exceeds the first set surface temperature TSA, any of the operating medium wavelength infrared heaters 210 is stopped. On the other hand, when the measured surface temperature TAX is lower than the second set surface temperature TSB, one of the non-operating medium wavelength infrared heaters 210 is operated.

  The first set surface temperature TSA is determined to be 150 ° C., for example. This is because when the surface temperature TA of the coated body 50 exceeds 150 ° C., the amount of evaporation of the solvent increases and adhesion between the binders is promoted. The second set surface temperature TSB is set to 100 ° C., for example. This is because when the surface temperature TA of the application body 50 is too low, the drying time of the application body 50 becomes longer.

Next, the heating of the application body 50 by the infrared heating device 200 will be described in comparison with the case of heating by the hot air heating device.
According to the warm air heating device, the surface of the application body 50 is heated, and then the heat of the surface is transmitted to the inside. For this reason, as the thickness of the application body 50 increases, the temperature difference between the surface and the inside increases. In particular, the following phenomenon occurs when the thickness of the coated body 50 exceeds 0.3 mm. As the solvent on the surface of the coated body 50 evaporates, the surface temperature TA rises, the binders adhere to each other, and a binder layer is formed. For this reason, the internal solvent does not evaporate and remains inside the coated body 50. When the positive electrode 10 is incorporated into the molten salt battery 1 with the solvent remaining, the solvent evaporates due to the heat generated by the molten salt battery 1 and the internal pressure increases. In addition, the battery life is reduced by the oxidation of the solvent.

  In addition, the binder density inside the coated body 50 may decrease. This is considered as follows. That is, the solvent is confined inside by the binder layer formed on the surface by hot air heating, thereby increasing the internal pressure. The internal pressure acts as a force that moves the internal binder and moves the binder to the surface. As a result, the binder density on the surface increases and the internal binder density decreases. When such a positive electrode 10 is incorporated in a molten salt battery, the following problem occurs. That is, when a binder layer is formed on the surface of the positive electrode 10, the binder is an insulating material and thus becomes an electric resistance layer, and the electrolytic solution is less likely to enter the positive electrode 10, so that the charging capacity or the charging speed is reduced. . Further, the decrease in the density of the binder inside the positive electrode 10 isolates the internal positive electrode active material from the current collector, and this positive electrode active material does not contribute to charging / discharging of the molten salt battery 1.

  Such a phenomenon occurs not only in the case of drying by hot air heating, but also by other heating means such as heating by an oven. In other words, the uneven heating of the application body 50 is caused particularly when the surface temperature TA of the application body 50 rises to the first set surface temperature TSA or more.

On the other hand, according to the heating by the infrared heating device 200, the following effects are exhibited.
The medium wavelength infrared light is transmitted to the inside of the coated body 50 as compared with light having a wavelength larger than 4 μm. Further, the medium wavelength infrared rays efficiently heat the application body 50 as compared with light having a wavelength of less than 2 μm. For this reason, compared with the said warm air heating apparatus etc., the temperature difference of the surface and the inside of the application body 50 does not become large.

Further, medium wavelength infrared rays are applied to the coated body 50 from above and below.
Since the intensity of medium-wavelength infrared light decreases as the distance from the light source increases, the temperature of the back side surface that is not irradiated with light is lower than the surface on the irradiation side when irradiated only from the direction. In this respect, since the medium wavelength infrared rays are irradiated from above and below, the temperature difference at each location in the thickness direction of the coated body 50 becomes small.

  In this way, the surface temperature TA is prevented from rising abnormally. For this reason, it is suppressed that the surface of the application body 50 dries earlier than the inside of the application body 50, and a binder layer is hardly formed when the binders on the surface adhere to each other.

  For this reason, the amount of the internal solvent remaining in the coated body 50 can be reduced. As a result, since the increase in the internal pressure of the coated body 50 is also suppressed, there is almost no movement of the binder accompanying the increase in the internal pressure, and the binder density difference between the surface of the positive electrode 10 and the inside becomes large. It is suppressed.

  Note that the decrease in the internal resistance of the positive electrode 10 due to the fact that the binder layer was not formed on the surface or the thickness of the binder layer was confirmed by comparing the voltage between terminals in high rate discharge. That is, it was confirmed that the terminal voltage of the molten salt battery 1 using the positive electrode 10 dried by the infrared heating device 200 was larger than the terminal voltage of the molten salt battery using the conventional positive electrode dried by hot air heating. .

With reference to FIG. 4, another example of the electrode manufacturing apparatus 100 will be described.
The electrode manufacturing apparatus 100 uses an induction heating apparatus 300 as the heating unit 130. Since the configuration other than the heating unit 130 has the same structure as that of the electrode manufacturing apparatus 100 described above, the description other than the heating unit 130 is omitted.

  The induction heating device 300 includes an induction coil 310, an AC power source 320, and a control unit 330 that controls a current and a frequency that flow through the induction coil 310. The control unit 330 once rectifies the AC frequency, further converts it to a predetermined frequency by an inverter, and causes the AC to flow through the induction coil 310. The frequency of alternating current flowing through the induction coil 310 is set between 50 kHz and 500 kHz.

  In the induction coil 310, the conductive wire is formed by twisting a plurality of conductive wires. The current collector 11 passes through the induction coil 310. The central axis of the induction coil 310 and the traveling direction of the current collector 11 are matched. That is, the magnetic field generated by the induction coil 310 and the traveling direction of the current collector 11 are matched.

  The controller 330 controls the amount of current flowing through the induction coil 310 based on whether the measured surface temperature TAX of the surface temperature sensor exceeds the first set surface temperature TSA. For example, when the measured surface temperature TAX exceeds the first set surface temperature TSA, the amount of current is decreased. On the other hand, when the measured surface temperature TAX is lower than the second set surface temperature TSB, the amount of current is increased.

Next, heating of the application body 50 by the induction heating apparatus 300 will be described.
When the current collector 11 passes through the induction coil 310, a current flows through the current collector 11 due to the magnetic field of the induction coil 310, thereby heating the current collector 11. Then, the current collector 11 is heated and the binder and the solvent are heated, whereby the solvent evaporates.

  The heating of the application body 50 by the induction heating device 300 also has the same effect as the heating of the application body 50 by the infrared heating device 200. That is, since the surface temperature TA is prevented from rising abnormally, the amount of the internal solvent remaining in the coated body 50 can be reduced. Moreover, since it is also suppressed that the internal pressure of the application body 50 increases, it is suppressed that the binder density difference between the surface of the positive electrode 10 and the inside becomes large.

(Effect of this embodiment)
(1) In the embodiment described above, the surface temperature TA of the coated body 50 to which the slurry is applied in the drying step is heated to be equal to or lower than the first set surface temperature TSA (set surface temperature). According to this structure, it can suppress that a binder density difference becomes large between the surface of the positive electrode 10, and the inside.

  (2) In the above embodiment, the surface temperature TA of the application body 50 is maintained at or below the first set surface temperature TSA in the drying step, and the temperature difference between the surface and the inside of the application body 50 coated with slurry is set to the set temperature range TSC. Keep inside and dry.

  According to this configuration, it is possible to suppress variation in the degree of drying inside the application body 50 and the degree of drying on the surface of the application body 50. That is, drying of the surface of the application body 50 before the inside is suppressed, and the amount of binder that moves from the inside to the surface is reduced. Thereby, the binder density difference of the surface in the thickness direction of the application body 50 and an inside can be made small.

  (3) In the above embodiment, the set temperature range TSC is set to 50 ° C. Thereby, compared with the case where it drys on the conditions from which the temperature difference of the surface of the application body 50 and an inside becomes larger than 50 degreeC, the binder density difference between the surface of the application body 50 and the inside can be made small.

  (4) In the above embodiment, the first set surface temperature TSA is set to 150 ° C. As a result, a binder layer is formed on the surface of the coated body 50 or the thickness of the binder layer is increased as compared with a case where the coated body 50 is dried under a condition where the surface temperature TA is higher than 150 ° C. This can be suppressed.

  (5) In the said embodiment, the infrared heating apparatus 200 with a wavelength of 2 micrometers-4 micrometers is used. Thereby, the application body 50 can be heated more efficiently than short wavelength infrared rays. Moreover, it can suppress that a difference arises between the dryness in the inside of the application body 50, and the dryness degree in the surface of the application body 50 compared with long wavelength infrared rays.

  (6) In the above embodiment, the induction heating device 300 is used. According to this configuration, the current collector 11 can be uniformly heated regardless of the surface and inside of the current collector 11. Thereby, it can suppress that the surface dries earlier than the inside of the application body 50.

  (7) In the said embodiment, the positive electrode 10 of the molten salt battery 1 is manufactured by the said manufacturing method. Since the positive electrode 10 is manufactured by the above manufacturing method, the binder density difference between the surface and the inside of the positive electrode 10 is small. That is, since the binder layer is not formed on the surface of the positive electrode 10 or the binder layer is thin, the increase in internal resistance due to the binder layer is small. That is, the charge capacity of the molten salt battery 1 can be increased as compared with a molten salt battery including the positive electrode 10 manufactured by a conventional manufacturing method.

  (8) In the above embodiment, in a battery using Na ions as a conductive species, a mixture of NaFSA and KFSA (molar ratio 56:44) is used as the electrolyte. According to this configuration, compared to a non-aqueous electrolyte secondary battery using the above organic substance as an electrolyte, the concentration of ions related to battery operation can be increased by an order of magnitude or more, and the ionic conductivity is also high. The rate can be increased.

Second Embodiment
A lithium ion capacitor is mentioned as a nonaqueous electrolyte electrochemical element. Hereinafter, embodiments will be described.

  The lithium ion capacitor includes a positive electrode, a negative electrode, and a separator. The positive electrode is formed by filling a positive electrode current collector with a positive electrode active material mainly composed of activated carbon. The negative electrode is formed by applying a negative electrode active material capable of inserting and extracting lithium ions to a negative electrode current collector (for example, a metal foil).

  As the positive electrode current collector, for example, a three-dimensional aluminum porous body is used. The porous aluminum body is obtained by burning urethane after covering the foamed urethane with aluminum. For example, a porous aluminum body having a porosity of 90% to 95% is used. Preferably, an aluminum porous body having a porosity of 93% is used.

  The negative electrode contains lithium ions or lithium. Lithium ions or lithium are occluded in the negative electrode having the above structure by an electrochemical method. For example, lithium metal is placed in advance in a lithium ion capacitor. Then, after assembling the lithium ion capacitor and before use as a secondary battery, the lithium ion capacitor is allowed to stand at a constant temperature condition for a predetermined period of time, so that lithium ions or lithium eluted from the lithium metal into the electrolyte are taken into the negative electrode. Make it.

As the separator, a polyethylene porous sheet having a thickness of 25 μm is used.
As the electrolytic solution, an organic electrolytic solution containing a lithium salt is used. For example, an organic electrolytic solution in which LiPF ₆ as a lithium supporting salt is dissolved at 1 mol / L in a mixed solution of ethylene carbonate and ethyl methyl carbonate is used.

<Method for producing positive electrode>
The positive electrode is formed by impregnating a porous aluminum body as a positive electrode current collector with a positive electrode active material paste.

The positive electrode active material paste is obtained by stirring a mixture of polyvinylidene fluoride as a binder and pyrrolidone as a solvent, activated carbon powder, and a conductive additive with a mixer.
By compression-molding the positive electrode, the activated carbon paste can be filled in the aluminum porous body at a higher density. Further, the thickness of the positive electrode is adjusted by adjusting the compression molding pressure. The thickness of the positive electrode after compression molding is preferably about 300 to 3000 μm.

<Method for producing negative electrode>
The negative electrode is formed by applying a negative electrode active material paste containing a negative electrode active material to a metal foil (negative electrode current collector).

  Natural graphite (hereinafter simply referred to as graphite) is used as the negative electrode active material. The negative electrode active material paste is obtained by stirring a mixture of polyvinylidene fluoride as a binder and pyrrolidone as a solvent, graphite, and ketjen black as a conductive additive with a mixer.

  The negative electrode is formed by applying a negative electrode active material paste to a copper metal foil as a negative electrode current collector by a doctor blade method, drying it, and then pressing it with a roller press or the like. The thickness of the negative electrode after molding is, for example, 150 μm.

  As a method for occluding lithium ions or lithium in the negative electrode, there are the following methods. A lithium metal foil is formed on the surface of the negative electrode formed by the above method, and a lithium ion capacitor is assembled using this negative electrode. Then, the assembled lithium ion capacitor is kept warm in a constant temperature layer at 60 ° C. for 24 hours. As a result, lithium ions or lithium eluted from the lithium metal foil into the electrolyte is occluded in the negative electrode.

(Example)
[1. Preparation of positive electrode]
100 parts by mass of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 5 μm), 2 parts by mass of ketjen black as a conductive additive, 4 parts by mass of polyvinylidene fluoride powder as a binder, and 15 parts of N-methylpyrrolidone as a solvent A positive electrode active material paste was prepared by adding parts and stirring with a mixer. As the positive electrode current collector, an aluminum porous body having a thickness of 1.0 mm, a porosity of 93%, and a cell diameter of 400 μm was used.

The positive electrode active material paste was filled in the positive electrode current collector so that the content of the activated carbon powder was 20 mg / cm ² . In the following description, the positive electrode current collector filled with the activated carbon positive electrode paste is referred to as a positive electrode sheet.

Next, the positive electrode sheet was dried with an infrared heating device. The surface temperature was 150 ° C., and the difference between the surface temperature and the internal temperature was 50 ° C. After drying, pressure was applied with a roller press (slit: 300 μm) to obtain a positive electrode. The thickness of the positive electrode after pressurization was 400 μm. The capacity of the positive electrode was 0.50 mAh / cm ² . In addition, the positive electrode thickness after pressurization became larger than the slit width by the spring back of the roller press machine.

[2. Production of negative electrode]
A copper foil having a thickness of 20 μm was used as the negative electrode current collector.
By adding 2 parts by mass of ketjen black as a conductive additive, 4 parts by mass of polyvinylidene fluoride powder as a binder, and 15 parts by mass of N-methylpyrrolidone as a solvent to 100 parts by mass of natural graphite powder, and stirring with a mixer, A negative electrode active material paste was prepared. The negative electrode active material paste was applied to the negative electrode current collector using a doctor blade. In the following description, a negative electrode current collector coated with a negative electrode active material paste is referred to as a negative electrode sheet.

Next, using a dryer, the negative electrode sheet was dried by heating at 100 ° C. for 1 hour to remove the solvent, and then pressurized with a roller press (slit: 100 μm) to obtain a negative electrode. The thickness of the negative electrode after pressurization was 75 μm. The obtained negative electrode had a capacity of 0.50 mAh / cm ² . Further, a 1 μm-thick lithium metal foil (equivalent to about 0.45 mAh / cm ² ) was formed on the surface of the negative electrode by a vacuum deposition method. This lithium metal foil is a lithium source for allowing the negative electrode to store lithium after the lithium ion capacitor is assembled.

[3. Fabrication of lithium ion capacitor]
The positive electrode and the negative electrode were cut into a size of 5 cm × 5 cm.
The positive electrode active material was removed from a part of the positive electrode, and an aluminum tab lead was welded to the removed portion of the positive electrode active material. Further, the negative electrode active material was removed from a part of the negative electrode, and a nickel tab lead was welded to the removed portion of the negative electrode active material.

Then, each electrode was transferred to a dry room and first dried at 140 ° C. for 12 hours in a reduced pressure environment. Furthermore, a polyethylene separator was sandwiched between the two electrodes to form a single cell element, and the single cell element was placed in a cell made of aluminum laminate. And electrolyte solution was inject | poured in the cell and the positive electrode, the negative electrode, and the separator were made to impregnate electrolyte solution. As the electrolytic solution, a solution in which 1 mol / L LiPF ₆ was dissolved in a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was used. Next, the aluminum laminate was sealed while decompressing the inside of the cell with a vacuum sealer. Then, lithium was occluded by the negative electrode by hold | maintaining a cell for 24 hours in a 60 degreeC thermostat.

(Effect of this embodiment)
According to this embodiment, the effect according to (1)-(6) of the said 1st Embodiment can be acquired. That is, in the manufacturing process of the positive electrode of the lithium ion capacitor, it is possible to suppress an increase in the binder density difference between the surface and the inside of the positive electrode by drying the positive electrode under the same conditions as in the first embodiment. it can.

  In addition, since the positive electrode of the lithium ion capacitor is manufactured by the above-described manufacturing method, a difference in binder density between the surface of the positive electrode 10 and the inside is reduced, and is a binder layer formed on the surface of the positive electrode 10? Or a binder layer becomes thin. That is, the increase in internal resistance due to the binder layer is small. For this reason, the charge capacity of the lithium ion capacitor including the positive electrode of the present embodiment is larger than that of the conventional lithium ion capacitor.

(Other embodiments)
In addition, the embodiment of the present invention is not limited to the embodiment exemplified in the above-described embodiment, and can be implemented by changing it as shown below, for example. The following modifications are not applied only to the above embodiments, and different modifications can be combined with each other.

  In the first embodiment, the mid-wavelength infrared heater 210 is operated in accordance with the surface temperature TA of the application body 50 in the drying process, but such control can be omitted. That is, even when the ambient temperature changes, a heating condition that is equal to or lower than the first set surface temperature TSA and within the set temperature range TSB is found, and the medium wavelength infrared heater 210 is operated under this heating condition. Even in this case, the same effect as the above manufacturing method can be obtained.

  In the first embodiment, as an example of the infrared heating device 200, the heating device configured by the medium wavelength infrared heater 210 is described, but the following configuration may be used instead. That is, the infrared heating device 200 can be configured by LEDs having a wavelength of 2 μm to 4 μm. In this case, since the radiation amount of the medium wavelength infrared light can be controlled by the duty control of the LED, the amount of light applied to the application body 50 can be controlled more accurately than in the case where the medium wavelength infrared heater 210 is used. it can.

  -In the said 1st Embodiment, although the heating part 130 is comprised by the specific heating means, the heating part 130 can also be comprised combining a heating means from which a type differs. For example, there are the following combinations. That is, a combination of the hot air heating device and the infrared heating device 200, the infrared heating device 200 and the induction heating device 300, the induction heating device 300 and the hot air heating device, and the hot air heating device, the infrared heating device 200, and the induction heating device 300 are combined. Conceivable.

  In the first embodiment, the magnetic field direction by the induction coil 310 and the moving direction of the current collector 11 are matched, but the magnetic field direction is not limited to this direction. The magnetic field direction may be perpendicular to the surface of the current collector 11. Further, the magnetic field direction and the width direction of the current collector 11 may be matched.

  -In the said 1st Embodiment, although the aluminum nonwoven fabric is used as the electrical power collector 11, an aluminum porous body, aluminum foil, etc. can be used besides this. Further, the current collector 11 may be formed of a corrosion-resistant material such as gold or platinum.

  In the above embodiment, the present invention is applied to a molten salt battery and a lithium ion capacitor as the nonaqueous electrolyte electrochemical element, but the present invention can also be applied to a nonaqueous electrolyte lithium ion secondary battery. In this case, the capacity can be increased as compared with the conventional case. The non-aqueous electrolyte lithium ion secondary battery has a low ionic conductivity due to its structure. Therefore, the current density is reduced by increasing the thickness of the positive electrode, but there is a merit because the capacity can be increased.

  In the above-described embodiment and modification, the application of the present invention to the positive electrodes of various batteries has been described. However, if the electrode is formed by drying a slurry applied to the current collector 11, the electrode The present invention can be applied to the production of (electrodes for non-aqueous electrolyte electrochemical elements).

  DESCRIPTION OF SYMBOLS 1 ... Molten salt battery, 10 ... Positive electrode (electrode for nonaqueous electrolyte electrochemical elements), 11 ... Current collector, 20 ... Negative electrode, 30 ... Separator, 40 ... Housing case, 41 ... Positive electrode case, 42 ... Negative electrode case, 43 DESCRIPTION OF SYMBOLS ... Sealing member, 44 ... Leaf spring, 50 ... Application body, 100 ... Electrode manufacturing apparatus, 110 ... Conveyance part, 111 ... 1st conveyance roller, 112 ... 2nd conveyance roller, 120 ... Application | coating part, 130 ... Heating part, DESCRIPTION OF SYMBOLS 140 ... Measurement part, 200 ... Infrared heating apparatus, 210 ... Medium wavelength infrared heater, 220 ... Control part, 300 ... Induction heating apparatus, 310 ... Induction coil, 320 ... AC power supply, 330 ... Control part.

Claims (8)

A method for producing an electrode for a non-aqueous electrolyte electrochemical device having a thickness of 0.3 mm or more,
An application step of applying a slurry containing an active material, a binder, and a solvent to a current collector;
A drying step of evaporating the solvent with a heating device,
In the drying step, the surface temperature of the coated body to which the slurry is applied is maintained at a set surface temperature or lower. A method for producing an electrode for a non-aqueous electrolyte electrochemical element. In the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements according to claim 1,
In the drying step, the surface temperature of the coated body is maintained below a set surface temperature, and the absolute value of the temperature difference between the surface temperature of the coated body coated with the slurry and the internal temperature is maintained within a set temperature range. The manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements characterized by these. In the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements according to claim 2,
The set temperature range is 50 ° C. The method for producing an electrode for a non-aqueous electrolyte electrochemical element, characterized in that: In the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements as described in any one of Claims 1-3,
The set surface temperature is 150 ° C. The method for producing an electrode for a non-aqueous electrolyte electrochemical element. In the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements as described in any one of Claims 1-4,
An infrared heating device having a wavelength of 2 μm to 4 μm is used as the heating device. A method for producing an electrode for a non-aqueous electrolyte electrochemical element. In the manufacturing method of the electrode for nonaqueous electrolyte electrochemical elements according to any one of claims 1 to 5,
An induction heating device is used as the heating device. A method for producing an electrode for a non-aqueous electrolyte electrochemical element.   A nonaqueous electrolyte electrochemical device comprising an electrode manufactured by the method for manufacturing an electrode for a nonaqueous electrolyte electrochemical device according to any one of claims 1 to 6.   A nonaqueous electrolyte electrochemical device comprising a positive electrode produced by the method for producing an electrode for a nonaqueous electrolyte electrochemical device according to any one of claims 1 to 6, wherein the electrolyte is a molten salt.

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