JP2008293970A - Electrode for electrochemical element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately compensate lithium equivalent to irreversible capacity in an active material layer of an electrode for an electrochemical element. <P>SOLUTION: The method of manufacturing the electrode for the electrochemical element, includes (i) a first step of supplying an active material on a surface of a collector to form an active material layer without lithium compensated, (ii) a second step of spraying moisture removal gas onto the active material layer without lithium compensated in decompressed atmosphere, (iii) after the second step, a third step of making the active material layer without lithium compensated absorb lithium to obtain an active material layer with lithium compensated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for an electrochemical device and a method for producing the same, and more particularly to a technique for supplementing lithium corresponding to an irreversible capacity with a precursor of an active material layer with high accuracy in a short time.

  2. Description of the Related Art In recent years, electronic devices have become rapidly portable and cordless, and there is an increasing demand for secondary batteries that are small, light, and have high energy density as power sources for driving these devices. In addition to small-sized consumer applications, technological developments for large-sized secondary batteries that require long-term durability and safety for power storage devices and electric vehicles are also accelerating. From such a viewpoint, an electrochemical element having a high voltage and a high energy density, particularly a nonaqueous electrolyte secondary battery, is expected as a power source for these applications.

The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a non-aqueous electrolyte. For the positive electrode, lithium cobalt oxide (for example, LiCoO ₂ ) having a high potential with respect to lithium as an active material, excellent in safety, and relatively easy to synthesize is used. For the separator, a microporous membrane made mainly of polyolefin is used. As the non-aqueous electrolyte, a non-aqueous electrolyte solution in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an aprotic organic solvent is used.

  For the negative electrode, a carbon material such as graphite is used as an active material. However, since graphite can occlude only one lithium atom with respect to six carbon atoms in theory, the theoretical capacity density of graphite is 372 mAh / g. Therefore, considering capacity loss due to irreversible capacity, graphite has a capacity of only about 310 to 330 mAh / g. The irreversible capacity corresponds to lithium that is stored in the negative electrode active material during charging and cannot return to the positive electrode active material during discharge.

  On the other hand, silicon (Si), tin (Sn), or germanium (Ge) that is alloyed with lithium is expected as an active material having a high theoretical capacity density. Si, Sn, and Ge simple substances, oxides, alloys, and the like have been studied. Among them, inexpensive Si and Si oxides have been widely studied.

However, since Si and Si oxide have a large irreversible capacity, it is necessary to further add an active material in an amount corresponding to the irreversible capacity to the positive electrode, and the battery design capacity is not increased as expected. Thus, a technique for compensating for lithium corresponding to the irreversible capacity has been proposed.
For example, lithium corresponding to an irreversible capacity can be compensated by attaching metallic lithium to the surface of the negative electrode active material layer not facing the positive electrode active material layer (see Patent Document 1).
Further, a technique for forming a lithium powder layer on at least one surface of a positive electrode, a negative electrode, and a separator has been proposed (see Patent Document 2).
Furthermore, a lithium metal layer is formed on the negative electrode by a dry film-forming method such as a vacuum deposition method or an ion plating method, and is stored in a dry atmosphere or in an electrolytic solution to store lithium in the active material layer of the negative electrode. A technique for improving the initial charge / discharge efficiency has been proposed (see Patent Document 3).
JP 2002-075454 A JP 2005-317551 A JP 2005-038720 A

  Although the irreversible capacity of Si, Si oxide, etc. is large, it is about 1 to 20 μm in terms of the thickness of the lithium layer. Based on this, Patent Document 3 is promising as a technology for uniformly filling lithium in the negative electrode, compared to Patent Document 1 in which a large amount of lithium is locally provided and Patent Document 2 in which the dispersibility of lithium powder is questionable. I think that the. However, even using the technique of Patent Document 3, it is difficult to sufficiently improve the initial charge / discharge efficiency by compensating for the irreversible capacity.

  The present invention has been made in view of the above, and an object of the present invention is to provide an electrode manufacturing method that can efficiently compensate for lithium corresponding to irreversible capacity and is suitable for mass production. The present invention is particularly effective when a high-capacity active material is used to increase the capacity of an electrochemical element such as a non-aqueous electrolyte secondary battery.

The present invention is a method of manufacturing an electrode having a conductive current collector, and an active material layer that occludes and releases lithium disposed on the surface of the current collector,
(I) a first step of supplying an active material to the surface of the current collector to form an active material layer not filled with lithium;
(Ii) a second step of spraying a moisture removal gas on the active material layer not filled with lithium in a reduced-pressure atmosphere;
(Iii) after the second step, a third step of obtaining an active material layer filled with lithium by occluding lithium in the active material layer not filled with lithium, and a method for producing an electrode for an electrochemical device About.

In the second step, the temperature of the moisture removing gas is preferably set to 100 ° C. or higher and 300 ° C. or lower.
In the second step, it is preferable to blow a gas onto the active material layer while cooling the lithium-unfilled active material layer.
It is preferable that the moisture removing gas sprayed on the active material layer not filled with lithium is a non-oxidizing gas.
The present invention is particularly effective when the active material contains at least one selected from the group consisting of silicon, tin, and germanium.
The second step is preferably performed in a state where the pressure in the reduced-pressure atmosphere is 613 Pa or less.
The present invention further relates to an electrode for an electrochemical device obtained by the above production method.

  When moisture is adsorbed on the surface of the active material layer, the adsorbed moisture reacts with lithium, and a part of lithium is inactivated. For this reason, all of the supplied lithium is not used to compensate for the irreversible capacity. Furthermore, it is extremely difficult to grasp and control the amount of lithium that is inactivated by moisture. Therefore, in the second step, moisture removal gas (for example, hot air) is blown onto the lithium-unfilled active material layer. Thereby, the water | moisture content adsorb | sucked to the active material layer can be removed smoothly, and the amount of lithium inactivated in a 3rd process can be reduced. That is, lithium corresponding to the irreversible capacity can be stored in the active material layer with high accuracy.

  According to the present invention, lithium corresponding to the irreversible capacity can be accurately supplemented to the active material layer. Therefore, even when a high-capacity material such as Si or Si oxide is used for the active material, it is possible to mass-produce the electrodes for electrochemical elements with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, a nonaqueous electrolyte secondary battery will be described as an example of an electrochemical element, and a negative electrode will be described as an example of an electrode.
First, the first step will be described.
In the first step, an active material is supplied to the surface of the current collector to form an active material layer not filled with lithium. This step can be performed using an apparatus as shown in FIG.
The apparatus of FIG. 1 includes a chamber 16 whose inside can be decompressed by a vacuum pump 17 and a vapor deposition system installed therein.
The vapor deposition system includes an unwinding roll 11 for supplying a current collector 19, a film forming roll A 14 a for forming a first vapor deposition zone, a vapor deposition source 13 a installed under the film forming roll A, and a component for forming a second vapor deposition zone. A film roll B14b, a vapor deposition source 13b installed below the film formation roll B, and a winding roll 15 for collecting a current collector having active material layers formed on both sides are provided.
The current collector 19 travels from the unwinding roll 11 toward the winding roll 15. The current collector 19 supplied from the unwinding roll 11 passes along the transport roll 10 a and travels along the peripheral surface of the film forming roll A. In the first vapor deposition zone, the second surface is exposed to the evaporation material while the first surface of the current collector is in contact with the peripheral surface of the film forming roll A.
After passing through the first vapor deposition zone, the current collector 19 passes through the transport rolls 10b, 10c, 10d, and 10e, turns inside out, and then travels along the peripheral surface of the film forming roll B. In the second vapor deposition zone, the first surface is exposed to the evaporation material while the second surface of the current collector is in contact with the peripheral surface of the film forming roll B.
The vapor deposition sources 13a and 13b are filled in crucibles 13x and 13y, respectively. By evaporating the vapor deposition sources 13a and 13b by methods such as electron beam irradiation and resistance heating, an evaporation material is supplied to the first vapor deposition zone and the second vapor deposition zone.
In the apparatus of FIG. 1, the current collector area for forming the active material layer is controlled by installing masks 12a and 12b having predetermined openings in the first vapor deposition zone and the second vapor deposition zone, respectively. The evaporation material is deposited on the surface of the current collector in each zone to form an active material layer that is not filled with lithium.

  Gas nozzles 18a and 18b are installed in the vicinity of the vapor deposition zone, and a reactive gas is allowed to flow into the evaporation material from the gas nozzle, whereby the evaporation material and the reactive gas are reacted to form an active material layer composed of a reaction product. You can also For example, oxygen is introduced as a reactive gas from the gas nozzle 18. In this case, the oxide of the material supplied from the vapor deposition source 13 can be vapor-deposited on the surface of the current collector 19, and an active material layer made of the oxide can be obtained.

Next, the second step will be described. In the second step, moisture removal gas is sprayed on the active material layer not filled with lithium in a reduced-pressure atmosphere. This step can be performed using an apparatus as shown in FIG.
The apparatus of FIG. 2 includes a chamber 30 whose inside can be decompressed by a vacuum pump 31, a water removal system installed therein, and a vapor deposition system.
The moisture removal system includes an unwinding roll 21 that supplies a current collector (hereinafter referred to as an electrode precursor 23) having an active material layer formed on both sides, and a gas nozzle 24 that injects a moisture removal gas.
The electrode precursor 23 supplied from the unwinding roll 11 passes through the vicinity of the gas nozzle 24 after passing through the transport rolls 20a and 20b. At that time, the moisture removing gas blown from the gas nozzle 24 collides with the active material layer, and the moisture is smoothly removed from the active material layer. By removing the water adsorbed on the active material layer, the amount of lithium to be deactivated can be reduced in the subsequent third step, as will be described later.
The moisture removing gas is preferably heated by the heater 25 and sprayed on the active material layer as hot air. When the temperature of the moisture removing gas is raised, the moisture is removed more smoothly than when the temperature is not raised.

The third step is performed in the apparatus of FIG. 2 following the second step. In the third step, an operation of occluding lithium in the active material layer not filled with lithium is performed.
After the moisture removing gas is sprayed, the electrode precursor 23 passes through the transport rolls 20c, 20d, 20e, and 20f and is sent to the vapor deposition system.
The vapor deposition system includes a film forming roll 27 that forms a vapor deposition zone, a vapor deposition source 28 installed under the film forming roll 27, and a winding roll 22 that collects an electrode supplemented with lithium.
The electrode precursor 23 travels along the peripheral surface of the film forming roll 27 after passing through the transport roll 20f. In the vapor deposition zone, the active material layer formed on one surface of the current collector is exposed to lithium vapor while the active material layer formed on the other surface is in contact with the peripheral surface of the film-forming roll.
In the apparatus of FIG. 2, the area of the active material layer that occludes lithium is controlled by installing a mask 29 having a predetermined opening in the vapor deposition zone.
The evaporation source 28 for supplying lithium vapor is filled in the crucible 28x. Metallic lithium can be used for the vapor deposition source 28. By evaporating the vapor deposition source 28 by a method such as electron beam irradiation or resistance heating, lithium vapor is supplied to the vapor deposition zone.
By flipping the current collector and repeating the second and third steps, lithium can be supplemented to the active material layer on the opposite side.

In the third step, when moisture is present on the surface of the active material layer, the adsorbed moisture and lithium may react to form a film made of a reaction product on the surface of the active material layer. Once this film is formed, the lithium supplied from the vapor deposition source 28 is only deposited on this film and is not occluded in the active material layer. For this reason, there arises a problem that lithium corresponding to the irreversible capacity is not supplemented in the active material layer.
In addition, when a battery is configured using an electrode on which a film is formed and charging / discharging is performed, the reaction area decreases, and thus the capacity decreases.
Further, in the case where lithium is occluded by a vacuum deposition method, moisture attached to the active material layer becomes water vapor due to heat during vapor deposition, and a part thereof reacts with lithium before reaching the active material layer. Therefore, a part of lithium is inactivated, and all of the charged lithium is not used for irreversible capacity compensation.

  On the other hand, by removing moisture adsorbed on the active material layer, it is possible to reduce the amount of lithium that is not compensated for in the active material layer and the amount of lithium that is inactivated. That is, lithium corresponding to the irreversible capacity can be stored in the active material layer with high accuracy.

In the second step, the temperature of the moisture removing gas is preferably set to 100 ° C. or more and 300 ° C. or less, and more preferably 200 to 300 ° C. When the temperature of the moisture removing gas is less than 100 ° C., the effect of increasing the temperature, that is, the effect of promoting moisture removal from the active material layer is reduced. On the other hand, when the temperature of the gas exceeds 300 ° C., the current collector that holds the active material layer may be softened. As a result, when the electrochemical device is configured and charging / discharging is repeated, it becomes susceptible to the stress due to the expansion and contraction of the active material layer.
The temperature of the moisture removing gas sprayed on the active material layer can be measured, for example, by installing a thermocouple at the tip of the air nozzle. In this case, the temperature of the gas can be regarded as the same as the temperature near the tip of the air nozzle.

In the second step, it is preferable to spray the moisture removing gas on the active material layer while cooling the lithium-unfilled active material layer. When hot air is blown onto the active material layer, the temperature of the active material layer and the current collector itself rises, the current collector is softened, and defects are likely to occur.
For example, as shown in FIG. 2, by cooling the active material layer 23 with the cooling can 26, moisture can be removed while suppressing the temperature rise of the active material layer 23. Therefore, moisture can be removed efficiently while preventing the current collector 19 from being softened and maintaining strength.

  The gas sprayed on the active material layer is preferably a non-oxidizing gas. When an oxidizing gas is used, the current collector surface may be oxidized, and the adhesion between the active material and the current collector may be reduced. The oxidation of the current collector surface is more likely to occur as the gas temperature increases. As the non-oxidizing gas, an inert gas (such as argon, helium, or nitrogen) or a reducing gas (such as hydrogen) can be used. When hydrogen or nitrogen is used as the gas blown to the active material layer, attention must be paid to reduction or nitridation of the active material layer or the current collector. Therefore, it is more preferable to use argon or helium.

  For example, when manufacturing the negative electrode of a nonaqueous electrolyte secondary battery, lithium metal, a lithium alloy, a carbon material (such as graphite, graphitizable carbon, and non-graphitizable carbon) can be used as the active material. However, the present invention is particularly effective when the active material contains at least one selected from the group consisting of silicon, tin, and germanium. These active materials have high capacity and high reactivity with lithium. Therefore, in the third step, lithium can be quickly occluded in the active material layer. In addition, silicon, tin, and germanium are hydrophilic and thus easily adsorb moisture compared to graphite. Therefore, the effect of removing moisture by blowing gas on the active material layer is increased. These active materials may be used individually by 1 type, and may be used in combination of 2 or more type.

As the active material containing silicon, for example, silicon (simple substance), a silicon oxygen substance such as SiO _x (0.05 <x <1.95), a part of silicon of the silicon oxygen substance may be Mg, Ni, Ti, Mo. A compound substituted with at least one selected from the group consisting of Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn can be used.
As the active material containing tin, Ni ₂ Sn ₄ , Mg ₂ Sn, SnO _x (0 <x <2), SnO ₂ , SnSiO ₃ , LiSnO, or the like can be used.

  Silicon oxide tends to adsorb moisture as the oxygen content increases. The cause is that oxygen in the active material easily forms hydrogen bonds with moisture, and the hydrophilicity increases. Further, when an active material layer made of, for example, silicon oxide is formed by reactive vapor deposition, oxygen is introduced into the chamber, so that the pressure in the chamber during film formation increases. For this reason, the mean free path of silicon evaporated from the evaporation source is shortened, and the straightness is reduced. As a result, the surface smoothness of the formed active material layer is reduced, the specific surface area is increased, and moisture is easily adsorbed.

  When the apparatus shown in FIG. 2 is used, the third step is performed in the decompressed chamber 30 after the second step. After the second step is performed in the air, the third step is performed in a reduced pressure atmosphere. A process may be performed. In this case, the process becomes complicated, but the same result can be obtained. However, after the second step, in order to suppress new moisture adsorption by the active material layer, it is necessary to thoroughly manage the moisture in the environment in which the current collector on which the active material layer is formed is stored. For example, it is desirable to store a current collector formed with an active material layer in an atmosphere of an inert gas such as Ar, in a vacuum, and in an environment with a dew point of −40 ° C. or lower.

  The second step is preferably performed in a state where the pressure in the reduced-pressure atmosphere is 613 Pa or less. At 613 Pa, the boiling point of water is 0 ° C. Therefore, when the second step is performed under a condition of 613 Pa or less, moisture contained in the active material layer is easily evaporated, and the amount of lithium to be deactivated can be efficiently reduced. Here, the lower limit value of the pressure in the second step is not particularly defined.

The present invention further relates to an electrode for an electrochemical device obtained by the above production method. Hereinafter, the electrode for an electrochemical element will be described in more detail.
There is no particular limitation on the method for forming the active material layer, and various methods can be used. However, in the third step, when lithium is occluded in the active material layer by a vacuum deposition method, if a material other than the active material (for example, a binder or a conductive agent) exists in the active material layer, the occlusion of lithium is prevented. There is a tendency to be disturbed. In view of this, in the present invention, it is preferable that the number of materials other than the active material contained in the active material layer is small, and it is more preferable that the active material layer is formed of only the active material. Examples of the method of forming the active material layer using only the active material include dry film forming methods such as vacuum deposition, sputtering, and ion plating.

The active material layer can contain optional components such as a binder and a conductive agent.
Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, and polyacrylic acid. Ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, Styrene butadiene rubber, carboxymethyl cellulose and the like can be used. Also selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene. Further, a copolymer of two or more kinds of materials may be used. A binder may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the conductive agent include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and conductive fibers such as carbon fiber and metal fiber. Metal powders such as carbon fluoride, aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene derivatives.

  A conductive substrate is used for the current collector. The current collector may be a non-porous material such as a metal foil, or may be a porous material such as punching metal or sponge metal. As the material of the current collector, for example, stainless steel, nickel, copper or the like is used. Although the thickness of a collector is not specifically limited, 5-100 micrometers is preferable and 8-50 micrometers is more preferable. If the thickness of the current collector is within this range, the electrode can be reduced in weight while maintaining the tensile strength of the electrode.

Hereinafter, the present invention will be described based on examples.
Example 1
(I) First Step Using the apparatus shown in FIG. 1, an active material was supplied to the surface of the current collector to form an active material layer that was not supplemented with lithium.
A strip-shaped copper foil (thickness 30 μm, average surface roughness Ra = 0.125 μm, manufactured by Hitachi Cable, Ltd.) was used for the current collector 19.
The inside of the vacuum vessel 16 was an argon atmosphere with a pressure of 3.5 Pa.
Si (scrap silicon: purity 99.999%) was used for the vapor deposition source 13.
Si vapor was generated from a vapor deposition unit including a vapor deposition source 13, a crucible, and an electron beam generator. At that time, the electron beam from the electron beam generator was polarized by the polarization yoke and then irradiated to the vapor deposition source 13. The Si vapor passed through the opening of the mask 12 and was deposited on both sides of the current collector 19.
The film formation rate of the active material layer was controlled to be 2 nm / second.
Thus, an electrode precursor 23 (thickness 50 μm) made of the current collector 19 having active material layers on both sides was produced.

(Ii) Second Step Using the apparatus shown in FIG. 2, gas was blown onto the active material layer not supplemented with lithium in a reduced pressure atmosphere.
The internal pressure of the vacuum vessel 30 was adjusted to 613 Pa.
Argon (99.999%) heated to 100 ° C. by the heater 25 was sprayed from the gas nozzle 24 toward the electrode precursor 23 at a flow rate of 10 sccm. At that time, the electrode precursor 23 was cooled by a cooling can 26 introduced with 5 ° C. water.

(Iii) Third Step Following the second step, lithium was occluded in the active material layer not supplemented with lithium in the apparatus of FIG. 2 to obtain an active material layer supplemented with lithium.
Lithium metal (Honjo Metal Co., Ltd.) was used for the vapor deposition source 28.
The evaporation source 28 was placed on a tungsten board and evaporated by resistance heating.
The Li vapor passed through the opening of the mask 29, adhered to the surface of the active material layer, and occluded in the active material layer. At this time, an amount of lithium corresponding to 12 μm in terms of thickness was occluded. The amount of lithium was measured by atomic absorption mass spectrometry (ICP) and converted to thickness assuming a porosity of 0%.

<< Examples 2 to 5 >>
Example 1 except that the temperature of the heater 25 was set to 50 ° C. (Example 2), 200 ° C. (Example 3), 300 ° C. (Example 4) and 400 ° C. (Example 5) in the second step. An electrode was prepared in the same manner as in Example 1.

Example 6
An active material layer was formed on both surfaces of the current collector under the same conditions as in Example 1 except that oxygen was introduced at a flow rate of 10 sccm from the gas nozzle 18 shown in FIG.
By introducing oxygen, Si and O ₂ reacted, and the reaction product was deposited on the surface of the current collector 19 as an active material.
As a result of measuring the composition of the active material layer by atomic absorption mass spectrometry, it was SiO _0.5 .
Using the electrode precursor thus obtained, an electrode was produced in the same manner as in Example 1.

Example 7
An electrode was produced in the same manner as in Example 6 except that the oxygen flow rate was 20 sccm.

<< Examples 8 to 11 >>
Example 6 except that the temperature of the heater 25 was set to 50 ° C. (Example 8), 200 ° C. (Example 9), 300 ° C. (Example 10) and 400 ° C. (Example 11) in the second step. An electrode was prepared in the same manner as in Example 1.

Example 12
In the second step, an electrode was produced in the same manner as in Example 4 except that the electrode precursor 23 was run so as not to contact the water-cooled can 26.

Example 13
An electrode was produced in the same manner as in Example 1 except that the internal pressure of the vacuum vessel 30 of the apparatus shown in FIG. 2 was adjusted to 1 × 10 ⁴ Pa.

<< Comparative Example 1 >>
An electrode was produced in the same manner as in Example 1 except that the second step was not performed.

<< Comparative Example 2 >>
An electrode was produced in the same manner as in Example 6 except that the second step was not performed.
The following evaluations were performed for each example and comparative example.
The results are shown in Table 1.

(Specific surface area measurement)
A current collector portion having an active material layer formed on both sides was cut out and used as a measurement sample. The specific surface area of the measurement sample was determined using a gas phase adsorption method (BET method). The measurement was performed immediately after the first step and before performing the second and third steps.

(Moisture content measurement)
After the second step, the electrode precursor 23 was taken out in an atmosphere controlled so that the dew point would not be −30 ° C. or higher, and the moisture content was measured by the Karl Fischer method in the same atmosphere. The size of the measurement sample was 2 cm × 5 cm (10 cm ² ). Specifically, the electrode precursor 23 was heated to 300 ° C. and held for 5 minutes while flowing in argon, and the amount of water generated in this 5 minutes was measured.

(Tensile strength)
After the second step, the tensile strength of the electrode precursor 23 was measured. The electrode precursor 23 was cut into a width of 6 mm and a length of 60 mm to obtain a measurement sample. Both ends in the longitudinal direction of the sample were fixed, tensile stress was applied in the longitudinal direction, and the maximum stress until the sample was cut was measured. The value obtained by dividing the maximum stress [N] by the cross-sectional area [mm ² ] of the sample was taken as the tensile strength [N / mm ² ].

(Degree of lithium storage)
After the third step, the degree of lithium occlusion of the electrode was evaluated by nuclear magnetic resonance (NMR). Specifically, the active material layer of the electrode was sampled, NMR measurement was performed, a peak intensity of 265 ppm attributed to metallic lithium was determined, and a value obtained by dividing the peak intensity by a predetermined value was defined as a “lithium occlusion degree”.
For the electrodes of Examples 1 to 5, 12 and 13 in which the active material was Si, the measured peak intensity was divided by the peak intensity of Comparative Example 1.
For the electrodes of Examples 6 and 8 to 11 in which the active material was SiO _0.5 , the measured peak intensity was divided by the peak intensity of Comparative Example 2.
For the electrode of Example 7 in which the active material was SiO _0.9 , the measured peak intensity was divided by the peak intensity of Comparative Example 3.

From the results in Table 1, it can be seen that the water content of the electrode precursor 23 is significantly reduced by performing the second step. Moreover, it turns out that this effect becomes more remarkable by raising the temperature of the gas sprayed on the active material layer in the second step.
When the amount of water is simply compared, the greater the proportion of oxygen present with respect to silicon in the active material, the more water is contained. This is presumably because oxygen and water in the oxide easily form hydrogen bonds. Further, it is considered that the greater the proportion of oxygen present, the greater the specific surface area of the active material layer affects the moisture content.
From the NMR evaluation (the degree of occlusion of lithium), it can be understood that lithium is easily occluded in the active material layer in the third step by reducing the water content.
From the above, it can be seen that according to the present invention, the active material layer can be efficiently supplemented with lithium corresponding to the irreversible capacity.

In the second step, when the temperature of the gas sprayed on the active material layer increases, the tensile strength slightly decreases. This is because the temperature of the electrode precursor 23 has increased and the current collector 19 has been softened. When this phenomenon becomes prominent, when an electrochemical device (for example, a nonaqueous electrolyte secondary battery) is configured and charged and discharged, the current collector 19 expands and contracts following the expansion and contraction of the active material, and the electrode Wrinkles may occur.
On the other hand, when the second step is performed while the electrode precursor 23 is cooled by the cooling can 26, good tensile strength can be maintained in the range where the gas temperature is within 300 ° C.
However, when the temperature of the gas is lower than 100 ° C., it is difficult for moisture to decrease, and the proportion of lithium that is not occluded in the active material layer increases.

  An electrochemical device including an electrode manufactured by the method of the present invention has a large capacity and excellent characteristics, so that it can drive a drive source of electronic equipment such as a notebook computer, a mobile phone, and a digital still camera, and also has a high output. It is useful as a power source for required power storage devices and electric vehicles. The production method of the present invention is particularly effective when a high-capacity active material such as a material containing Si is used, but the same effect can be obtained even when applied to an electrode having an active material layer containing graphite.

It is a schematic diagram which shows an example of the apparatus which implements a 1st process. It is a schematic diagram which shows an example of the apparatus which implements a 2nd and 3rd process.

Explanation of symbols

10a, 10b, 10c, 10d, 10e, 10f Transport roll 11 Unwind roll 12a, 12b Mask 13a, 13b Deposition source 13x, 13y Crucible 14a Film forming roll A
14b Deposition roll B
DESCRIPTION OF SYMBOLS 15 Winding roll 16 Chamber 17 Vacuum pump 18a, 18b Gas nozzle 19 Current collector 20a, 20b, 20c, 20d, 20e, 20f, 20g Conveying roll 21 Unwinding roll 22 Winding roll 23 Electrode precursor 24 Gas nozzle 25 Heater 26 Cooling Can 27 Film forming roll 28 Deposition source 28x Crucible 29 Mask 30 Chamber 31 Vacuum pump

Claims (7)

A method for producing an electrode comprising: a conductive current collector; and an active material layer that occludes and releases lithium disposed on a surface of the current collector,
(I) a first step of supplying an active material to the surface of the current collector to form an active material layer not filled with lithium;
(Ii) a second step of spraying a moisture removing gas on the active material layer not filled with lithium in a reduced-pressure atmosphere;
(Iii) after the second step, a third step of obtaining an active material layer supplemented with lithium by occluding lithium in the active material layer not filled with lithium to produce an electrode for an electrochemical device Method.   The method for producing an electrode for an electrochemical element according to claim 1, wherein, in the second step, the temperature of the moisture removing gas is set to 100 ° C or higher and 300 ° C or lower.   3. The method for producing an electrode for an electrochemical element according to claim 1, wherein, in the second step, the moisture removing gas is sprayed onto the active material layer while cooling the lithium-unfilled active material layer.   The method for producing an electrode for an electrochemical element according to claim 1, wherein the moisture removing gas is a non-oxidizing gas.   The manufacturing method of the electrode for electrochemical elements in any one of Claims 1-4 in which the said active material contains at least 1 sort (s) selected from the group which consists of silicon, tin, and germanium.   The method for producing an electrode for an electrochemical element according to any one of claims 1 to 5, wherein, in the second step, the pressure of the reduced-pressure atmosphere is 613 Pa or less.   The electrode for electrochemical elements obtained by the manufacturing method in any one of Claims 1-6.

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