KR20120002433A - Electrode for electrochemical device and method for production thereof - Google Patents

Abstract

PURPOSE: An electrode for an electrochemical device and a manufacturing method thereof are provided to control exfoliation in an interface of an active material layer and a conductive layer by supplying an electrode for a electrochemical device with a superior withstand voltage characteristic and low resistance. CONSTITUTION: A conductive layer(3) is formed on a surface of a current collector(1) and contains a conductive carbon particle and a first binder. An active material layer(2) is formed on the surface of the conductive layer and contains an active material particle and a second binder. The conductive carbon particle includes a small particle group and a large particle group. The peak of the volume particle size distribution of the small particle group is included in a range of 3-7μm. The peak of the volume particle size distribution of the large particle group is included in the range of 10-20μm. The interference of the conductive layer and the active material layer has a roughness over a maximum height Rmax of 10μm. The first binder and the second binder do not respectively have a double bond with carbon.

Description

Electrode for Electrochemical Device and Manufacturing Method Thereof {ELECTRODE FOR ELECTROCHEMICAL DEVICE AND METHOD FOR PRODUCTION THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for an electrochemical device having low resistance and excellent high current characteristics. For example, a capacitor such as an electric double layer capacitor (EDLC) and a pseudo capacitor (P-EDLC), a lithium ion battery, or a nickel hydrogen storage battery The present invention relates to an electrode used for a battery such as the above.

Recently, from the viewpoint of energy saving, environmental conservation and the use of petroleum alternative energy, technology development using electrochemical devices such as secondary batteries and electric double layer capacitors (EDLC), mainly in automobiles, is progressing, and hybrid vehicles (HEV) and PEV The development of electric vehicles is accelerating. In addition, the use of high-performance secondary batteries and EDLCs is progressing in solid state drive type hard disks and the like.

The electrode for electrochemical elements generally has an electrical power collector and the active material layer formed in the surface. However, when the active material layer is directly formed on the surface of the current collector, the electrode resistance may increase, the current collector may be oxidized, or hydrogen embrittlement may occur. Therefore, it is proposed to form the conductive layer containing electroconductive carbon particles as a 1st layer on the surface of an electrical power collector, and to form an active material layer as a 2nd layer on the surface (patent document 1, 2).

Japanese Unexamined Patent Publication No. 2009-38387 Japanese Patent Publication No. 2005-508081

With the increase in the performance of electrochemical devices, there is a growing demand for the development of electrodes for electrochemical devices with excellent high current characteristics. However, only by forming a conductive layer on the surface of the current collector, it is difficult to obtain an electrode having a low resistance enough to satisfy the recently demanded high current characteristics. In addition, the voltage applied to the electrochemical device is gradually increasing, and high withstand voltage characteristics are required for the electrode.

In view of the above situation, an object of the present invention is to provide an electrode for an electrochemical device having low resistance and excellent withstand voltage characteristics that can satisfy sufficient high current characteristics.

That is, one aspect of this invention is formed in the electrical power collector and the surface of an electrical power collector, and the conductive layer containing electroconductive carbon particle and a 1st binder, and the surface of an electroconductive layer, and active material particle and a 2nd The active material layer containing a binder, electroconductive carbon particle contains a small particle group and a large particle group, the peak of the particle size distribution of a small particle group exists in the range of 3-7 micrometers, and the volume of a large particle group The peak of particle size distribution exists in the range of 10-20 micrometers, and the weight ratio (small particle group / large particle group) of a small particle group and a large particle group is 95/5-50/50, and is between a conductive layer and an active material layer. The interface of is related with the electrode for electrochemical elements which has a roughness whose maximum height Rmax is 10 micrometers or more.

This invention also provides the effective method of manufacturing the electrode for electrochemical elements with low resistance.

That is, another aspect of this invention applies the 1st slurry containing said electroconductive carbon particle, a 1st binder, and a 1st liquid component to the surface of (i) an electrical power collector, and forms a electrically conductive coating film. The step of (ii) heating the conductive coating film by radiant heat to volatilize the first liquid component from the conductive coating film, and (iii) the step (ii), on the surface of the conductive coating film, the active material particles and the second binder. And a step of applying a second slurry containing a second liquid component to form an active material coating film, and (i) drying the laminate of the conductive coating film and the active material coating film to at least one of radiant heat and warm air. The manufacturing method of the electrode for this is related.

Since the electrode for electrochemical elements which concerns on this invention has extremely low resistance at the interface of a conductive layer and an active material layer, it is low in resistance and excellent in a large current characteristic. Moreover, peeling at the interface between the conductive layer and the active material layer is unlikely to occur, and is excellent also in the breakdown voltage characteristic. According to the production method according to the present invention, an electrode for an electrochemical device having low resistance and excellent high current characteristics and withstand voltage characteristics can be efficiently produced.

While the novel features of the invention are set forth in the appended claims, the invention is better understood by the following detailed description taken in conjunction with the accompanying drawings, together with other objects and features of the present invention, both in terms of construction and content. Will be understood.

1A is a schematic longitudinal cross-sectional view showing an example of a conventional electrode structure.
1B is a schematic longitudinal cross-sectional view showing another example of the conventional electrode structure.
1C is a schematic longitudinal cross-sectional view showing an example of the electrode structure according to the present invention.
FIG. 2A is an example of a cross-sectional SEM photograph of an example of an electrode according to a comparative example. FIG.
2B is an example of a cross-sectional SEM photograph of another example of the electrode according to the comparative example.
FIG. 2C is a cross-sectional SEM photograph example of one example of an electrode according to the embodiment of the present invention. FIG.
FIG. 3 is a view showing a calculation line and a curve line for the roughness curve of FIG. 2C. FIG.
FIG. 4 is a diagram illustrating a distance Rmax-n between the calculation line and the curve of FIG. 3.

The electrode for electrochemical elements which concerns on this invention is formed in the electrical power collector, the surface of an electrical power collector, the conductive layer containing electroconductive carbon particle and a 1st binder, and the surface of a conductive layer, and also the active material particle, An active material layer containing a second binder is provided.

It is important to form an interdiffusion layer between the conductive layer and the active material layer in order to obtain an electrode having a low resistance and excellent excellent withstand voltage characteristics to satisfy the recently demanded high current characteristics. The interdiffusion layer is formed by diffusing the conductive carbon particles and the first binder contained in the conductive layer to the active material layer side, and diffusing the active material particles and the second binder contained in the active material layer to the conductive layer side.

The presence of such interdiffusion layer can be confirmed by measuring the maximum height Rmax of the roughness of the interface between the conductive layer and the active material layer. When the interdiffusion layer is formed, the maximum height Rmax is 10 µm or more. When the maximum height Rmax is 10 µm or more (for example, 13 µm or more, 14 µm or more or 15 µm or more), that is, when the interdiffusion layer is formed, the interface resistance between the conductive layer and the active material layer becomes extremely small. The adhesion between the conductive layer and the active material layer is increased, and it is possible to obtain an electrode having desired low resistance and withstand voltage characteristics. However, since the electrode characteristic may become unstable when the maximum height Rmax exceeds 25 micrometers, it is preferable that it is 25 micrometers or less.

The maximum height Rmax of the roughness of the interface between the conductive layer and the active material layer can be measured in a cross section perpendicular to the plane direction of the current collector of the electrode. In the cross section, a boundary between conductive carbon particles and active material particles is observed. The trajectory (hereinafter, roughness curve) of the point moving this boundary corresponds to the interface between the conductive layer and the active material layer. The maximum height Rmax of the roughness curve is obtained by the predetermined method described below.

In addition, an electrochemical element mainly means a capacitor and a battery, For example, an electric double layer capacitor (EDLC), a pseudo capacitor (P-EDLC), a lithium ion battery, a nickel hydrogen storage battery, etc. are contained. Although the structure of a capacitor and a battery is not specifically limited, Coin type, a winding type, a laminated type, etc. are contained.

Next, the structure of the electrode for electrochemical elements conventionally and this invention is demonstrated using schematic longitudinal cross-sectional view of an electrode.

1A and 1B show a conventional electrode structure, and FIG. 1C shows an electrode structure of the present invention. Here, the case where the active material layer 2 is provided on one surface of the current collector 1 will be described. However, the electrode concerning this invention is not limited to the aspect of FIG. 1C, The case where the active material layer 2 and the conductive layer 3 are provided in the one surface of the electrical power collector 1, The case where the active material layer 2 and the conductive layer 3 are provided on both surfaces is included.

In FIG. 1A, the active material layer 2 is directly formed on one main surface of the current collector 1. The structure shown in Fig. 1A is most commonly employed in batteries and EDLCs, and a large number of portable devices and personal computers have electrochemical elements having this structure. However, in this structure, current collection performance is limited, and it is difficult to satisfy the demand for recent large current characteristics.

In FIG. 1B, the conductive layer 3 is formed on one main surface of the current collector 1, and the active material layer 2 is formed on the surface of the conductive layer 3. However, since no interdiffusion layer is formed between the active material layer 2 and the conductive layer 3, the interface resistance between the conductive layer and the active material layer is large, and the adhesion between the conductive layer and the active material layer is also lowered. Therefore, the desired low resistance and withstand voltage characteristics cannot be obtained, and for example, peeling is likely to occur between layers after 50 to 100 cycles of charge and discharge.

In FIG. 1C, the conductive layer 3 is formed on one main surface of the current collector 1, the active material layer 2 is formed on the surface of the conductive layer 3, and the active material layer 2 is electrically conductive. An interdiffusion layer 4 is formed between the layers 3. When the interdiffusion layer 4 is enlarged, the boundary of electroconductive carbon particle and active material particle is observed, and a roughness curve considerable at the interface between a conductive layer and an active material layer can be obtained from this boundary. When the maximum roughness Rmax of the roughness curve is 10 µm or more, it is possible to reduce the electrode resistance to 1/3 to 1/10 when the interdiffusion layer 4 is not provided. In addition, the charge-discharge cycle characteristics of the electrochemical device are also greatly improved.

Next, the electrode for electrochemical elements which concerns on this invention is demonstrated in detail.

The electrode includes a current collector, a conductive layer formed on the surface of the current collector, and an active material layer formed on the surface of the conductive layer. The current collector is usually in the form of a sheet, and the conductive layer and the active material layer may be formed only on one main surface of the current collector, or may be formed on both main surfaces.

Metal foil is used preferably for an electrical power collector. The thickness of metal foil is 8-60 micrometers, for example, Preferably it is 20-40 micrometers. As a constituent element of metal foil, Al, Ni, Cu etc. are mentioned, for example. Aluminum foil is preferably used for the capacitor electrode or the positive electrode of the lithium ion battery. Moreover, copper foil is used preferably for the negative electrode of a lithium ion battery. The metal foil may be a plain foil not subjected to etching treatment or may be an etching foil. A plain foil can expect high withstand voltage characteristics. Etching foil is excellent in adhesiveness with a conductive layer. The current collector may have a structure processed in three dimensions, for example, a punching foil or a lath gold mesh current collector may be used.

The conductive layer contains conductive carbon particles and a first binder.

It is preferable to use graphite material for electroconductive carbon particle. The graphite material is a generic term for a carbon material having a graphite region, and any of natural graphite (phosphorous graphite, earthy graphite, etc.), heat treated material of natural graphite, and artificial graphite can be used.

The mean particle size of the conductive carbon particles (volume particle size median diameter D ₅₀ of the distribution) is preferably, 5~20㎛. If the average particle diameter is too large, the particle gap may be large and the resistance value may be large. If the average particle diameter is too small, it may be difficult to form irregularities at the interface between the conductive layer and the active material layer.

In this invention, in order to make the maximum height Rmax of the roughness of the interface between a conductive layer and an active material layer into 10 micrometers or more, the mixed particle containing a small particle group and a large particle group is used for electroconductive carbon particle. By mixing large particle | grains and small particle | grains in electroconductive carbon particle, it becomes easy to form the interdiffusion layer with the largest height Rmax of 10 micrometers or more which is dense and excellent in adhesiveness between a conductive layer and an active material layer. As a result, adhesiveness between a conductive layer and an active material layer becomes large and the resistance of an electrode becomes small.

More specifically, the volume particle size distribution of the conductive carbon particles has peaks on the small particle diameter side and the large particle diameter side, respectively. Conductive carbon particles having such a particle size distribution can be regarded as mixed particles including a small particle group and a large particle group. Here, it is also important that the peak of the volume particle size distribution of the small particle group is in the range of 3-7 micrometers, and the peak of the volume particle size distribution of the large particle group is in the range of 10-20 micrometers. It is thought that a dense interdiffusion layer is formed because electroconductive carbon particle has such a particle size distribution.

The mean particle size of the small particle group, and (median diameter D ₅₀ in the volume particle size distribution) is 3~7㎛, the mean particle size of the large particle group is preferably in the 10~20㎛. It is thought that a large particle group mainly contributes to the improvement of electroconductivity in a conductive layer, and a small particle group mainly contributes to the adhesiveness of an interdiffusion layer.

In addition, a volume particle size distribution can be measured with a laser diffraction type particle size distribution measuring apparatus (Microtrac MT3300EXII by Nikkiso Corporation).

It is also important to set the weight ratio (small particle group / large particle group) of the small particle group and the large particle group to 95 / 5-50 / 50, preferably 90 / 10-70 / 30. It is thought that the structure of the interdiffusion layer at the interface between the conductive layer and the active material layer becomes dense because the small particle group accounts for 50 to 95% by weight of the conductive carbon particles contained in the conductive layer.

The weight ratio of the small particle group and the large particle group can be obtained by waveform separation of the obtained volume particle size distribution, obtaining the volume ratio of the small particle group and the large particle group, and converting the volume ratio into the weight ratio. However, when both the small particle group and the large particle group are graphite materials, the volume ratio can be regarded as the weight ratio.

As for ratio (D1 / D2) of the average particle diameter D1 of a small particle group, and the average particle diameter D2 of a large particle group, 1.5 or more and 5 or less are preferable, and 2 or more and 3.5 or less are especially preferable. By using such a particle diameter ratio, the density of the interdiffusion layer is improved and the strength of the conductive layer itself is also greatly improved.

The conductive carbon particles may contain carbon black in addition to graphite. As carbon black, acetylene black, Ketjen black, etc. can be used. The conductive layer containing carbon black is advantageous in that volume resistance and sheet resistance tend to be reduced. The amount of carbon black is preferably 20 to 110 parts by weight based on 100 parts by weight of the conductive carbon particles contained in the conductive layer.

When the electrode is required to have a withstand voltage characteristic of 2.5 V or more, in the conductive layer, a resin having no melting point between carbons and having a melting point of 160 ° C. or higher and a thermosetting resin are preferably used in the first binder. Such resins are excellent in voltage resistance characteristics and heat resistance. For example, since at least 1 sort (s) chosen from the group which consists of an acrylate resin, a polyimide resin, a polyamideimide resin, a fluororesin, and a cellulose resin is stable, it is preferable. Moreover, an acrylate resin, polyamideimide resin, and a cellulose resin are especially preferable at the point which can obtain a high binding force in a small quantity. Especially, an acrylate resin is the most preferable at the point which is excellent in redox resistance.

In recent years, in the field of electrochemical devices such as EDLC, development of electrolyte solvents having excellent withstand voltage characteristics, such as HCF ₂ CH ₂ -O-CF ₂ CF ₂ H, has been developed. High voltage of more than 2.5V, about 4.2 ~ 4.5V in lithium ion batteries) is required. The above resin is also excellent in terms of satisfying such a request.

An acrylate resin is a generic term of resin containing the unit of acrylic acid or its alkyl ester or methacrylic acid, or its alkyl ester. According to the fluorinated acrylate resin obtained by substituting a part of hydrogen atoms contained in the main chain of an acrylate resin or an alkylester group with fluorine, the oxidation-reduction resistance of an electrode can be improved further and the outstanding charge / discharge cycle characteristics can be obtained. For example, emulsions in which fluorinated acrylate resins are dispersed in water are commercially available.

As the fluorine resin, for example, polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) can be used. Fluorine resin is excellent in acid resistance and alkali resistance.

Although a cellulose resin is not specifically limited, Ethyl cellulose is preferable from a viewpoint of stability of the slurry which is a precursor of a conductive layer, film forming property, leveling property, adhesiveness, etc. of the coating film (conductive coating film) of a slurry.

As the thermosetting resin, one having a Tg of 260 ° C. or higher is preferable, for example, an addition type thermosetting imide (polyimide resin) having an allyl group at both terminals and a polyamideimide resin are preferable. When using a thermosetting resin, it is preferable to perform heat processing for about 30 minutes at 200-300 degreeC finally as a hardening process as needed.

On the other hand, when the electrode withstand voltage characteristic of 2.1 V or more and 2.7 V or less is required, at least one selected from the group consisting of olefin resin, synthetic rubber and fluorine resin is preferably used for the first binder. As synthetic rubber, styrene butadiene rubber (SBR), nitrile rubber (NBR), ethylene propylene rubber (EPM, EPDM), etc. are mentioned, for example. As olefin resin, polyolefin, such as polyethylene (PE), polypropylene (PP), modified PE, modified PP, is mentioned, for example. Synthetic rubber is excellent in the point which is excellent in adhesive force and can provide moderate flexibility to an electrode. Moreover, an olefin resin is excellent at the point of low price. However, the carbon-to-carbon double bond included in the synthetic rubber may react with oxygen in EDLC to which a high voltage of more than 2.5 V is applied or lithium ion battery to which a high voltage of about 4.5 V is applied, and the durability characteristic is slightly deteriorated. There is a case. In addition, the electrode containing a (modified) polyolefin may deteriorate when heated to 130 degreeC or more.

You may make carboxymethylcellulose (CMC) contain in a 1st binder from a viewpoint of providing moderate viscosity to the slurry which is a precursor of a conductive layer. For example, when using the emulsion and CMC which disperse | distributed the fluorinated acrylate resin in water together, since CMC melt | dissolves in water and gives moderate viscosity to a slurry, preparation of a uniform slurry becomes easy.

By using said 1st binder, the high heat resistance EDLC electrode which has a withstand voltage characteristic over 2.1V or more than 2.5V, and can be dried at high temperature about 160 degreeC can be obtained, for example. Moreover, the electrode for lithium ion batteries to which the voltage exceeding 4.2V is applied can be obtained.

In the conductive layer, the amount of the first binder is preferably 1 to 20 parts by weight, more preferably 3 to 10 parts by weight or 3 to 6 parts by weight per 100 parts by weight of the conductive carbon particles. In addition, when using CMC and another binder together, 0.5-30 weight% is suitable for the weight ratio of CMC to the whole 1st binder.

In one embodiment of the present invention, the conductive layer is a compound having a triazine ring (eg, triazine 2,4,6-trimercapto-s-triazine monosodium salt, 2,4,6-trimercapto- s-triazinetrisodium salt and the like). The compound having a triazine ring assists the first binder to improve the binding force between the conductive carbon particles or the binding force between the current collector and the conductive layer. The triazine ring is excellent in oxidation resistance and suppresses gas generation in the electrochemical element. 1-12 weight part is suitable with respect to 100 weight part of electroconductive carbon particles, and, as for the quantity of the compound which has a triazine ring, 1-3 weight part is more suitable.

Although the thickness of a conductive layer changes with kinds of electrode, it is 5-20 micrometers, for example in the case of an electric double layer capacitor, and 10-40 micrometers, for example in the case of a lithium ion secondary battery. In the case where the conductive layer is thick and has a thickness of, for example, 10 to 20 µm, it is particularly important to mix and use a small particle group and a large particle group as described above from the viewpoint of securing high conductivity.

An active material layer is formed on the surface of the conductive layer.

The active material layer contains active material particles and a second binder. However, the constituent material of the active material layer is not limited to these. For example, conductive additives such as carbon black may be included as optional components.

In the case of the electrode for electric double layer capacitors, activated carbon is used as an active material particle. In this case, both the positive electrode (anode) and the negative electrode (cathode) similarly contain activated carbon as an active material. On the other hand, in the case of the pseudo capacitor, various materials are used for the active material particles. For example, activated carbon is used for the positive electrode and graphite is used for the negative electrode.

Also in the case of the lithium ion battery electrode, various materials are used for an active material particle. As the anode, a transition metal compound or the like is used. As the transition metal compound, a lithium-containing transition metal oxide or an olivine acid (LiFePO ₄ ) type compound including at least one selected from the group consisting of Co, Ni and Mn is preferably used. Graphite, silicon, a silicon compound, etc. are used for a cathode. As the silicon compound, silicon carbide or silicon oxide is preferably used.

In the case of an electrode for nickel hydrogen storage batteries, nickel hydroxide is used for the positive electrode and hydrogen storage alloy is used for the negative electrode for the active material particles.

Although the present invention can be applied to any of these electrodes, application to the electrodes for electric double layer capacitors and pseudo capacitors is most effective.

It is preferable to use the material shown as a 1st binder as a 2nd binder in an active material layer. Although the 2nd binder may be a material different from a 1st binder, it is preferable to use the same material from a viewpoint of improving adhesiveness of a conductive layer and an active material layer. For example, when using a fluorinated acrylate resin (FA) as a 1st binder, it is preferable to use a fluorinated acrylate resin (FA) also for a 2nd binder. The same applies to the use of CMC.

In the active material layer, the amount of the second binder varies depending on the type of the electrode, but, for example, in the case of the electric double layer capacitor or the pseudo capacitor, 3 to 10 parts by weight, or 4, based on 100 parts by weight of the active material particles (active carbon or graphite). 6 weight part is suitable. When the amount of the second binder increases, the adhesion between the conductive layer and the active material layer is improved, but the DC resistance and the AC resistance (ESR) tend to increase. When there is too little 2nd binder amount, there exists a tendency for the adhesiveness of active material particle to fall. When using CMC and another binder together, 0.5-50 weight% is suitable for the weight ratio of CMC to the whole 2nd binder.

In one form of this invention, an active material layer contains the compound which has the same triazine ring as mentioned above. The compound having a triazine ring assists the second binder to improve the binding force between the active material particles or the binding force of the conductive layer and the active material layer. As for the quantity of the compound which has a triazine ring, 1-3 weight part is suitable for 100 weight part of active material particles.

Although the thickness of an active material layer changes with kinds of electrodes, in the case of an electric double layer capacitor, it is 50-200 micrometers, for example. In addition, in the case of a coin type electrochemical element, the thickness of an active material layer is 400-700 micrometers.

Next, the manufacturing method of the electrode for electrochemical elements which concerns on this invention is demonstrated.

Process (i)

The first slurry containing the conductive carbon particles, the first binder, and the first liquid component is prepared.

It is more preferable that the viscosity of a 1st slurry is 200-4000 mPa * s (200-4000cp) and 400-2200 mPa * s (400-2200 cP) at 20 degreeC from the point which is excellent in workability and mass productivity. In the viscosity measuring apparatus, it measures at the rotation speed of 100 rpm using the B-type viscometer (DIGITAL VISMETRON VDH-W) of Shibaura Systems Co., Ltd., and No. 5 rotor. Although the preparation method of a 1st slurry is not specifically limited, For example, what is necessary is just to mix the solution, dispersion liquid, or emulsion containing a conductive carbon particle and a 1st binder, and a 1st liquid component using various mixing apparatuses.

What is necessary is just to select suitably for a 1st liquid component according to the kind of 1st binder. For example, when using the emulsion which disperse | distributed the fluorinated acrylate resin which is an acrylate resin in water, and CMC together, a 1st liquid component is water. Instead of emulsions of acrylate resins, even when emulsions or dispersions of synthetic rubbers such as polytetrafluoroethylene and SBR are used, water can be used as the first liquid component. Even when using an aqueous solution in which a cellulose resin such as ethyl cellulose is dissolved in water, the first liquid component is water. On the other hand, when using polyvinylidene fluoride, it is preferable to use organic components, such as N-methyl- 2-pyrrolidone (NMP). More specifically, the first slurry can be obtained by mixing a solution, an emulsion or a dispersion liquid containing the first binder with the conductive carbon particles, and adding a predetermined liquid component, if necessary, and mixing. You may add the compound which has a triazine ring to a 1st slurry.

Next, a 1st slurry is apply | coated to the surface of an electrical power collector, and a conductive coating film is formed.

When the conductive coating film is formed on one main surface of the current collector, various coaters such as a slot die coater, a roll coater, and a cam coater can be used as the coating device. . On the other hand, when forming a conductive coating film simultaneously in both main surfaces of an electrical power collector, it is preferable to use a dip coater, for example. Dip coaters are inexpensive and produce electrodes more efficiently.

Process (ii)

Next, the conductive coating film is heated by radiant heat to volatilize the first liquid component from the conductive coating film. In that case, it is preferable not to completely dry a conductive coating film, but to stop drying in the state in which the conductive coating film contained the 1st liquid component of some quantity. When radiant heat is used, since a liquid component preferentially decreases from the inside of a conductive coating film, a liquid component tends to remain in the vicinity of the surface of a conductive coating film. In such a state, by forming the active material layer on the surface of the conductive layer, mutual diffusion easily occurs between the conductive layer and the active material layer.

Drying is preferably stopped when the conductive coating film is in a tacky dry state. The touch-dried state means a dry state such that the surface of the conductive coating film does not collapse even when the finger touches it. In such a state, it is thought that many 1st liquid components are distributed in the surface side rather than the electrical power collector side of a conductive coating film.

On the other hand, in the conventional drying by hot air or warm air (convective heat), the liquid component preferentially decreases from the vicinity of the surface of the conductive coating film. Therefore, mutual diffusion hardly occurs between the conductive layer and the active material layer. When radiant heat is used in this step, it is possible to reduce the electrode resistance to 1/2 to 1/10 as compared with the case of using warm air.

As radiant heat, it is preferable to use infrared energy (0.7-1000 micrometers), especially thermal energy of far infrared rays (for example, wavelength 4-1000 micrometers). For example, as a heat source that emits far infrared rays, heat sources such as electric, heating, and gas can be used. It is preferable to control the temperature of the dry conductive coating film to 130-180 degreeC, and a dry atmosphere is atmospheres, such as nitrogen and air. In addition, the temperature or radiation temperature of a coating film can be measured with a globe thermometer.

However, in the case where the first liquid component is an organic component such as NMP, there is a possibility of ignition, so that not only radiant heat such as far infrared rays but also hot air (fresh air or nitrogen, etc.) of about 150 ° C. is blown to a dry atmosphere. It is preferable. On the other hand, when the first liquid component is water, the conductive coating film can be easily dried using radiant heat.

Process

A second slurry containing the active material particles, the second binder, and the second liquid component is prepared. Also about the viscosity of a 2nd slurry, it is more preferable that it is 800-4000 mPa * s (800-4000cp) and 1500-2200 mPa * s (1500-2200 cP) at 20 degreeC from the point which is excellent in workability and mass productivity. The viscosity can be measured in the same manner as in the first slurry. The preparation method of a 2nd slurry is not specifically limited, either, For example, what is necessary is just to mix the solution, dispersion liquid, or emulsion containing an active material particle and a 2nd binder, and a 2nd liquid component using various mixing apparatuses. What is necessary is just to select suitably according to the kind of 2nd binder also about. You may add the compound which has a triazine ring to a 2nd slurry.

Next, a 2nd slurry is apply | coated to the surface of a conductive coating film, and an active material coating film is formed. In that case, it is preferable to apply | coat a 2nd slurry to the surface of the electrically conductive coating film of a contact dry state as mentioned above. When the conductive coating film is formed only on one main surface of the current collector, for example, a slot die coater, a roll coater, a cam coater or the like is used. In addition, when the conductive coating films are formed on both main surfaces of the current collector, for example, it is preferable to apply the second slurry to the surfaces of both conductive coating films simultaneously using a dip coater.

Process

The laminated body of the electrically conductive coating film and active material coating film which were obtained by the said process (iii)-(iii) is dried by at least one of radiant heat and warm air. At this time, it is preferable to dry by radiant heat as much as possible from a viewpoint of drying efficiency. As described above, in the drying by the warm air convection, drying proceeds from the surface of the coating film, whereas when radiant heat is used, the temperature rises from the inside of the coating film, so that the drying efficiency increases. When drying advances from the coating film surface, it becomes difficult for the moisture inside a coating film to escape. Moreover, when moisture escapes, it is easy to cause a crack in a coating film. Moreover, when drying advances from the coating film surface, since a surface Higel layer is formed, resistance becomes large.

In the drying in this step, it is preferable to completely volatilize the first liquid component and the second liquid component remaining from the laminate to complete the electrode. When a liquid component remains in an electrode, the liquid component may be carried in to an electrochemical element, and the performance of an electrochemical element may deteriorate. It is preferable to control the temperature of the laminated body in drying at 130-180 degreeC, and a dry atmosphere is not specifically limited, An air atmosphere is preferable.

In order to improve stability of the first and second slurries, stabilizers may be added to these slurries. For example, when a slurry contains acetylene black or Ketjen black, since the lifetime of a slurry tends to fall, the addition of a stabilizer is effective. Moreover, since the 1st slurry for forming a conductive layer contains graphite (large particle group) with a big particle diameter, it is easy to gelatinize and it may become difficult to apply | coat to the surface of an electrical power collector. In this case also, the addition of stabilizers is effective.

As a stabilizer of a slurry, the polymer which has isoprene sulfonic acid group is preferable. The sulfonic acid group may form a sodium salt, for example, may have a structure such as -CH (SO ₃ Na) -CH (CH ₃ ) .CH-CH _2- . The position of bonding the sulfonic acid group is not particularly limited. Since isoprene sulfonic acid group has a hydrophobic group and a hydrophilic group, it is effective as a surfactant which disperse | distributes the structural component of a slurry, and is excellent also in compatibility with a binder component etc. For example, a polymer having a structure in which isoprene sulfonic acid group and a hydrophobic group (for example, styrene group) are arranged in a block shape in one molecular chain is preferable in view of high dispersion stability.

As for the addition amount of the stabilizer to a 1st and 2nd slurry, 3-7 weight% is preferable with respect to the total amount of solid content in a slurry. If it is less than 3 weight%, the effect is small, and if it exceeds 7 weight%, an electrode manufacturing cost will become high. The stabilizer having an isoprene sulfonic acid group is thought to facilitate the formation of the interdiffusion layer and also contribute to lowering the resistance of the electrode.

Next, a series of processes in the manufacturing method of the electrode which concerns on this invention are illustrated.

[First form]

First, the conductive coating film A is formed on one main surface of the current collector, and is heated with far infrared rays to dry the conductive coating film A to the dry touch state. Next, the active material coating film A is formed on the surface of the conductive coating film A, and the whole is heated in far infrared rays and completely dried. Thereafter, the current collector is inverted to form a conductive coating film B on the other main surface of the current collector, heated with far infrared rays, and the conductive coating film B is dried to a dry contact state. Next, the active material coating film B is formed on the surface of the conductive coating film B, and the whole is heated in far infrared rays and completely dried. In this method, a predetermined step is repeated for each side of the current collector.

[Second form]

First, the conductive coating films A and B are formed on both main surfaces of the current collector in turn by using a dip coater or sequentially using a slot die coater, a roll coater, a cam coater, and the like, and heated with far infrared rays to form the conductive coating film A. And B is dried to the touch dry state. Subsequently, at the same time or sequentially, the active material coating films A and B are formed on the surfaces of the conductive coating films A and B, and the whole is heated in far infrared rays and completely dried. This method is advantageous in that the drying of the conductive coating films A and B can be performed simultaneously, and the active material coating films A and B can be dried simultaneously.

On the other hand, when drying by convection of warm air is performed instead of drying by far infrared rays, it takes a long time to dry and cannot form a desired interdiffusion layer between the conductive layer and the active material layer.

Next, an electric double layer capacitor will be described as an example of the electrochemical element including the electrode according to the present invention.

The electric double layer capacitor includes an electrode including activated carbon as the active material and an electrode group including a porous separator interposed between the electrodes. The electrode group may be a laminated type or a wound type. In the case of the stacked type, a plurality of electrodes having an active material layer on both surfaces are stacked through a separator between the electrodes, and a pair of electrodes having an active material layer on one side is disposed on the outermost side of the laminate, and the current collector is turned outward. Place it. On the other hand, in the case of the winding type, a pair of strip-shaped electrodes is prepared, and it winds along the longitudinal direction of an electrode through a separator between them. Then, the obtained electrode group is accommodated in a predetermined case, and the electrode group is impregnated with the nonaqueous electrolyte. As a result, the nonaqueous electrolyte is impregnated into the pores provided by the electrode and the separator.

The nonaqueous electrolyte solution consists of a nonaqueous solvent in which a supporting salt is dissolved. As the supporting salt, for example, a boron quaternary ammonium salt (for example, tetraethylammonium boride, triethylmethylammonium boride) or the like is used. In addition, the non-aqueous solvent may include a cyclic carbonate which may have a fluorine atom, a chain carbonate which may have a fluorine atom (for example, propylene carbonate), a chain ether which may have a fluorine atom, a cyclic ether which may have a fluorine atom, and fluorine. The lactone which may have an atom, the sulfolane derivative which may have a fluorine atom, the non-fluorine ester solvent which does not have a fluorine atom, a nitrile solvent, frans, oxolanes, etc. are mentioned. Among these, in order to obtain the capacitor which is excellent in a breakdown voltage characteristic, it is preferable to use the nonaqueous solvent containing the alkyl fluoride. An alkyl fluoride is a general term for the compound which substituted at least one part of the hydrogen atom of dialkyl ether by the fluorine atom. Specific examples include HCF ₂ CH ₂ -O-CF ₂ CF ₂ H, CF ₃ CF ₂ CH ₂ -O-CF ₂ CF ₂ H, and the like.

Although the ratio of the alkyl fluoride occupies in the whole nonaqueous solvent changes with the apparatus to which a capacitor is applied, it is preferable to set it as 5 weight% or more, and it is more preferable to set it as 10-30 weight%. If it is less than 5 weight%, the effect of improving breakdown voltage characteristics is small, and if it exceeds 30 weight%, there exists a tendency for cost to become high. In addition, the internal resistance may increase or gas generation may be present.

By using the electrode and the nonaqueous electrolyte, it is possible to obtain an electric double layer capacitor having excellent withstand voltage characteristics having, for example, a rated voltage of 2.1 V or more or 2.5 V or more, and a voltage rating of 3 V or more. However, if the applied voltage exceeds 3.5V, the first or second binder decomposes depending on the type, causing gas generation. Therefore, the rated voltage is preferably 3.5V or less. On the other hand, by using a binder having a high withstand voltage characteristic, it is also possible to achieve a breakdown voltage characteristic of about 4.7V.

Next, although an Example demonstrates this invention more concretely, this invention is not limited to a following example.

`` Example 1 ''

EDLC electrodes having compositions of various conductive layers and active material layers were produced and evaluated.

(a) first slurry

According to the composition of the conductive layer shown in Table 1, the material was mixed with the mixer and the 1st slurry whose viscosity in 20 degreeC is 1000 mPa * s was prepared.

The material is shown in detail below.

Graphite (small particle group): Particles having a volume particle size distribution having a peak at 6 mu m (average particle diameter 6 mu m) and having a volume diameter of at least 90 volume% of 3 to 7 mu m

Graphite (large particle group): Particles having a volume particle size distribution having a peak at 18 mu m (average particle diameter 18 mu m) and having a particle diameter of 10-20 mu m or more at 90 vol% or more

Slurry Stabilizer: Water-Soluble Polymer with IsopreneSulfonic Acid Group

First binder

FA: Fluorinated Acrylate Emulsion

SBR: Styrene Butadiene Latex

CMC: carboxymethyl cellulose

PI: Solvent Type Polyimide

PTFE: Polytetrafluoroethylene

PVDF: polyvinylidene fluoride

PAI: Polyamideimide

EC: ethyl cellulose

(b) a second slurry

According to the composition of the active material layer shown in Table 2, the material was mixed with the mixer and the 2nd slurry whose viscosity in 20 degreeC is 1500 mPa * s was prepared.

The material is shown in detail below.

Second binder

TA: triazine

The detail of another 2nd binder is the same as that of a 1st binder.

Active material: activated carbon, average particle diameter 8 μm

AB: Acetylene black, primary particle diameter 0.03 micrometer

KB: Ketjen Black, primary particle diameter 0.03㎛

The 1st slurry was apply | coated to one main surface of the aluminum foil of 20 micrometers in thickness, the electrically conductive coating film of 35 micrometers in thickness was formed, and 1st drying was performed. Then, the 2nd slurry was apply | coated to the surface of a conductive coating film, the active material coating film of thickness 130micrometer was formed, and 2nd drying was performed. Then, the 1st slurry was apply | coated to the other main surface of aluminum foil, the electrically conductive coating film of 35 micrometers in thickness was formed, and 1st drying was performed. Then, the 2nd slurry was apply | coated to the surface of a conductive coating film, the active material coating film of thickness 130micrometer was formed, and 2nd drying was performed. Both the first drying and the second drying performed copying or convection drying in the same manner as follows.

Radiation: Heats coating film at 130 degrees Celsius for 1 minute by far infrared rays

Convection: By warm air of 130 degrees Celsius, coating film is heated for five minutes

On the other hand, the wavelength of far infrared rays was made into 4-1000 micrometers, and the electric heater was used for the heat source which radiates far infrared rays.

When thermosetting resin was used for the binder (Sample Nos. 11 and 15), heat treatment was performed at 200 ° C. for 30 minutes as a curing treatment at the final stage of drying.

[evaluation]

(Iv) Presence of mutual diffusion layer

A SEM photograph of a cross section perpendicular to the plane direction of the current collector of the electrode was taken to confirm the presence or absence of the interdiffusion layer. Specifically, the maximum height Rmax of the roughness of the interface between the conductive layer and the active material layer was determined.

When the maximum height Rmax is 13 µm or more, "○",

When the maximum height Rmax is 10 µm or more and less than 13 µm, "△",

When maximum height Rmax was less than 10 micrometers, it showed in Table 3 by "x".

(Ii) adhesion

A tape was attached to the surface of the active material layer, a spring balance was attached to one end thereof, and tension was performed at a speed of 2 mm for one second. The reading of the maximum intensity at the time of peeling was made into adhesive strength. The same measurement was performed 3 times (n = 3) and the average was taken.

In the case of 230gf / cm or more `` ○ '',

In the case of 180gf / cm or more and less than 230gf / cm, "△",

In the case of less than 180 gf / cm, it indicated in Table 3 by "x".

Surface cracks

The overview of the electrode after completion of the second drying was observed.

When a crack is observed `` ○ ''

When no crack was observed at all, it was indicated in Table 3 by "×".

(Iii) Impregnation of electrolyte

TEABF ₄ (tetraethylammonium fluoride) was dissolved in propylene carbonate (PC) at a concentration of 1 mol / L to prepare a nonaqueous electrolyte solution. 1 micrometer L of the obtained electrolyte solution was dripped at the electrode, and time until the impregnation was visually confirmed was measured.

If the electrolyte is completely impregnated within 5 seconds, "○",

When the electrolyte solution was completely impregnated within 5 seconds and exceeded 15 seconds, it was indicated in Table 3 by "(triangle | delta)."

(Iii) ESR at 3V

Using each electrode, 18 mm 50 L type 50F wound EDLC was produced and ESR was measured on the conditions of 1 KHz and 1 mA of current using the ACRENT LCR meter "E4284A". The results are shown in Table 3.

(Iii) withstand voltage characteristics

About EDLC used above, at 70 degreeC, the voltage of 3V was continuously applied, and after 300 hours, EDLC expanded, and the presence or absence of abnormality, such as leakage, was investigated.

When no expansion or leakage occurs due to gas generation, `` ○ '',

When slight expansion is observed, "△"

Obviously, expansion or leakage was observed in Table 3 as "x".

2A, 2B, and 2C are examples of cross-sectional SEM photographs of electrodes of Sample No. 8, Comparative Example No. 12, and Sample No. 5 according to the Example, respectively, of Comparative Examples. In FIG. 2B, the interdiffusion layer is formed between the conductive layer and the active material layer, whereas in FIG. 2C, the interdiffusion layer is formed.

Next, a method of obtaining the maximum height Rmax will be described in detail by taking the sample shown in FIG. 2C as an example.

[Measurement of Maximum Height Rmax]

First, a SEM photograph of a cross section perpendicular to the plane direction of the current collector of the electrode is taken. The magnification is 1000 times, and an image is taken with a digital camera. At that time, the scale reference line (10 mu m) is displayed on the moving image (FIG. 2C). In this cross section, this image in which the boundary between the conductive carbon particles and the active material particles is observed is put into a personal computer, and a roughness curve (curve a) is drawn on the boundary between the conductive carbon particles and the active material particles by image processing or the like.

Next, the length (for example, xcm) of the image image of the scale reference line (10 micrometers) is measured, and the standard line b of 80 micrometers equivalent length L (L = 8xcm) is drawn on two images. These two standard lines are arrange | positioned in parallel with the surface direction of an electrical power collector, and are moved so that it may contact the peak part of a curve (a), and a valley part (refer FIG. 3). The obtained line is called a calculation line and a curve line, respectively. A vertical line is drawn from the calculation line to the curve, and the length T of the interval between the calculation line and the curve is obtained (see Fig. 4). Length T is converted into actual length using the scale reference line, and it is set as maximum height Rmax-n.

The above operation is performed at two positions of the right reference and the left reference for one SEM photograph (N = 2), and the average value of Rmax-1 and Rmax-2 is set to Rmax-12. In the case of the right reference, the above operation is performed by matching the right end of the standard line of length L with the right end of the SEM photograph. In the case of the left reference, the above operation is performed by matching the left end of the standard line of length L with the left end of the SEM photograph. The same operation is repeated with respect to three SEM photographs, and the average value of three Rmax-12 is calculated | required (N = 6), and it is set as Rmax.

Table 4 shows the data of the maximum height Rmax obtained for the sample numbers 1, 2, 5, and 6. In addition, the data of the maximum height Rmax of the electrode (sample numbers 1-2, 6-2) produced similarly to sample numbers 1 and 6, and the small particle group / large particle except the point which dried by the convection method instead of the radiation method. Except that the weight ratio of the group was 5/95, the data of the maximum height Rmax of the electrodes (Sample No. 19) produced as in Sample Nos. 1, 2, 5, and 6 are also shown simultaneously.

[Review]

When the coating film was dried by radiant heat, any evaluation result was good, but when drying by warm air, the interdiffusion layer was not formed and any evaluation result was insufficient.

As compared with the case where only the small particle group or the large particle group of the graphite particles of the conductive layer were used, the formation of the interdiffusion layer was improved and the 3V withstand voltage characteristics were also improved when this was used in combination at a predetermined ratio. The improvement of the adhesiveness of a conductive layer and an active material layer is considered to have an influence here.

In the electrode (No. 8) of the comparative example in which the conductive layer was not formed, the resistance was large, and the withstand voltage characteristic was also greatly deteriorated. From this, it is recognized that the conductive layer greatly contributes to the reduction of the resistance of the electrode and the improvement of the breakdown voltage characteristic.

Particularly good characteristics can be obtained when an acrylate resin or a cellulose resin is used as the binder. In particular, in the case of using a cellulose resin, the slurry stability was excellent, and the film forming property was good. When SBR was used, the 3V withstand voltage characteristics were slightly lowered, but the AC resistance (ESR) was smaller than when fluorinated acrylate, PTFE or PVDF was used. When fluorine resins, such as PTFE and PVDF, were used, the impregnation of electrolyte solution fell slightly, and the binder amount for ensuring sufficient adhesiveness tended to become comparatively large.

Especially when the acrylate resin, polyimide, polyamideimide, or cellulose resin was used as a binder, the favorable characteristic was acquired. The cellulose resin was especially effective in improving the adhesiveness of an electrical power collector and a coating film.

When triazine was added as an auxiliary agent for the binder, further improvement in adhesion was observed, and in particular, remarkable improvement in withstand voltage characteristics was seen.

On the other hand, in the above embodiment, the EDLC has been described. However, the present invention can also be manufactured in the same manner as the EDLC electrode for the pseudo capacitor or the secondary battery electrode, and thus the same effect can be expected even when applied to them.

Since the electrode for electrochemical elements which concerns on this invention is low in resistance, and excellent in a large current characteristic and withstand voltage characteristic, it is applicable to various uses. Among them, it is effective in large electrochemical devices applied to large industrial machines such as construction machines such as automobiles and cranes.

According to the present invention, an electrode having a high withstand voltage characteristic of 2.5 V or more can be obtained, but the present invention can be naturally applied to an electrochemical device requiring a sustained voltage (CCV: Closed Circuit voltage) of 2.1 V or more. As such an electrochemical element, the large electric double layer capacitor which can charge and discharge at high electric current of 100 A or more is mentioned, for example.

While the present invention has been described with respect to preferred embodiments at this point in time, such disclosure should not be interpreted limitedly. Various modifications and variations will be apparent to those skilled in the art upon reading the above disclosure. Accordingly, the appended claims should be construed as including all modifications and alterations without departing from the true spirit and scope of the present invention.

1 current collector
2 active material layer
3 conductive layers
4 Interdiffusion Layer

Claims (12)

With the whole house,
A conductive layer formed on the surface of the current collector and further comprising conductive carbon particles and a first binder;
It is formed on the surface of the said conductive layer, and further comprises the active material layer containing active material particle and a 2nd binder,
The said electroconductive carbon particle contains a small particle group and a large particle group,
The peak of the volume particle size distribution of the said small particle group exists in the range of 3-7 micrometers,
The peak of the volume particle size distribution of the said large particle group exists in the range of 10-20 micrometers,
The weight ratio (small particle group / large particle group) of the said small particle group and the said large particle group is 95/5-50/50,
The interface between the said conductive layer and the said active material layer has the roughness whose maximum height Rmax is 10 micrometers or more, The electrode for electrochemical elements. The method according to claim 1, wherein the first binder and the second binder, each having no carbon double bond, a thermoplastic resin having a melting point of 160 ° C or more, or Tg comprises a thermosetting resin cured product of 260 ° C or more, Electrochemical device electrode. The electrode for electrochemical elements according to claim 1, wherein the first binder and the second binder each include at least one member selected from the group consisting of olefin resins, synthetic rubbers, and fluororesins. The amount of the said 1st binder is 3-6 weight part with respect to 100 weight part of said electroconductive carbon particles, The quantity of the said 2nd binder is the said active material particle in any one of Claims 1-3. The electrode for electrochemical elements which is 3-6 weight part with respect to 100 weight part. The electrode for electrochemical elements according to any one of claims 1 to 3, wherein at least one of the conductive layer and the active material layer contains 0.5 to 3 wt% of a compound having a triazine ring. The electrode for electrochemical elements as described in any one of Claims 1-3 whose said electroconductive carbon particle is a graphite material. The electrode for electrochemical elements according to any one of claims 1 to 3, wherein the active material particles are activated carbon, graphite, silicon, a silicon compound, a transition metal compound, or a hydrogen storage alloy. (Iii) applying the first slurry containing conductive carbon particles, a first binder, and a first liquid component to the surface of the current collector to form a conductive coating film,
(Ii) heating the conductive coating film by radiant heat to volatilize the first liquid component from the conductive coating film,
(Iii) after the step (ii), applying a second slurry containing active material particles, a second binder, and a second liquid component to the surface of the conductive coating film to form an active material coating film;
(Iii) a step of drying the laminate of the conductive coating film and the active material coating film with at least one of radiant heat and warm air,
The said electroconductive carbon particle contains a small particle group and a large particle group,
The peak of the volume particle size distribution of the said small particle group exists in the range of 3-7 micrometers,
The peak of the volume particle size distribution of the said large particle group exists in the range of 10-20 micrometers,
The weight ratio (small particle group / large particle group) of the said small particle group and the said large particle group is 95/5-50/50 The manufacturing method of the electrode for electrochemical elements. The method according to claim 8, wherein in the step (ii), the dry state of the conductive coating film is made into a dry contact state,
The manufacturing method of the electrode for electrochemical elements which apply | coats a said 2nd slurry to the surface of the said electrically conductive coating film of the said contact-dry state in the said process (iii). The thermoplastic resin having no melting point between carbons and having a melting point of 160 ° C or higher, or Tg containing a thermosetting resin of 260 ° C or higher as the first binder or the second binder. The manufacturing method of the electrode for electrochemical elements which mixes a solution, a dispersion liquid, or an emulsion, and the said electroconductive carbon particle or the said active material particle, and prepares the said 1st slurry or the said 2nd slurry. The solution, dispersion or emulsion containing at least one selected from the group consisting of an olefin resin, a rubber-like polymer and a fluorine resin, and the conductive carbon particles or the active material particles are mixed with each other. The manufacturing method of the electrode for electrochemical elements which prepares the said 1st slurry or the said 2nd slurry. The manufacturing method of the electrode for electrochemical elements of Claim 8 or 9 which adds the stabilizer which has isoprene sulfonic acid group to the said 1st slurry and the said 2nd slurry.

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