JP2008103118A - Electrode for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for achieving thinness of an electrode and high density of an active material simultaneously and for achieving improvement in output characteristics without using a binder and a conductive material in a secondary battery. <P>SOLUTION: The electrode for the battery includes a current collector and an active material layer containing an active material formed on the surface of the current collector. The active material layer includes whiskers to hold the active material on the surface of the current collector. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery electrode. In particular, the present invention relates to an improvement for improving the output characteristics of a battery.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, a lithium ion secondary battery having the highest theoretical energy among all the batteries is attracting attention, and is currently being developed rapidly. Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material, a conductive material, and the like are applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode active material, a conductive material, and the like using a binder. The negative electrode applied to both surfaces is connected via an electrolyte layer and is housed in a battery case.

  The lithium ion secondary battery used as a motor drive power source for automobiles as described above has extremely high output characteristics as compared with consumer lithium ion secondary batteries used in mobile phones, laptop computers, etc. The current situation is that research and development is underway to meet such demands.

  The above-described binder and conductive material are essential for the electrode, and a technique for increasing the output of a secondary battery using these is disclosed (see Patent Document 1). However, since these occupy about several ten percent of the electrode material, the proportion of the active material is relatively low, which is not preferable for improving the energy density and the output density. Therefore, development of a novel electrode that does not contain a binder or a conductive material is required.

  In addition, thinning of the electrode for the purpose of improving the output density has been studied.

  For example, a method of increasing the surface area by reducing the particle diameter of the active material to increase the area of reaction activity is conceivable. Furthermore, according to this method, the active material layer becomes thin and the number of electrode layers per unit volume can be increased. Therefore, it is considered that the output density can be greatly improved while maintaining the energy density. However, if the electrode is made thinner by reducing the particle diameter of the active material, it becomes difficult for the conductive material to form an electrical network. Therefore, more conductive material must be added, and if the energy density is to be maintained, the output density can be lowered. Even if the particle size of the conductive material is reduced so as to be proportional to the particle size of the active material, the particle size of the conductive material is usually much smaller than the particle size of the active material. There is a limit to the conversion. In addition, since the contact resistance is increased, the average particle size of about 10 to 20 μm is the limit for reducing the particle size of the active material. Furthermore, since it is difficult to reduce the thickness of the current collector as will be described later, even if the number of electrode layers is increased, the proportion of the active material layer hardly increases, and eventually it is difficult to realize a high output density.

Further, in order to reduce the ratio of the current collector per volume and mass, and to improve the volume energy density, the mass energy density, and the output density, it has been studied to make the current collector thinner. However, since the conductive material and the binder are indispensable electrode constituent materials, it is necessary to apply them to the surface of the current collector when manufacturing the electrode. In this coating process, it is required to apply the current collector while maintaining the micron level while providing smoothness in a tensioned state. Therefore, the strength required to withstand the tension is required to be at least about 15 to 20 μm, and a desired film thickness has not been achieved. Therefore, increasing the number of electrode layers as described above has little effect. Under such circumstances, there is a strong demand for the development of a battery electrode having high output characteristics that can be used for a motor drive secondary battery that requires high output.
JP 11-296371 A

  In view of the various problems as described above, in the present invention, without using a binder and a conductive material, the thinning of the electrode and the increase in the density of the active material are realized at the same time, thereby improving the output characteristics. It aims to provide a means.

  The present invention is a battery electrode including a current collector and an active material layer formed on the surface of the current collector, wherein the active material layer holds the active material on the surface of the current collector There is provided a battery electrode characterized by comprising whiskers.

  Holding the active material on the surface of the current collector using conductive whiskers eliminates the need for a binder and conductive material, so it is possible to reduce the thickness of the electrode and increase the density of the active material at the same time. It becomes possible to achieve the improvement.

  Embodiments of the present invention will be described below. In addition, the electrode in this invention means the laminated body of a collector and an active material layer. In addition, the drawings referred to in the present application are merely schematically shown, and do not define various conditions of each component, various conditions between components, and the like.

(First embodiment)
The present invention provides a battery electrode including a current collector and an active material layer including an active material formed on a surface of the current collector, wherein the active material layer collects the active material. A battery electrode comprising a whisker held on a surface of an electric body.

  In FIG. 1, sectional drawing of the electrode for batteries of this embodiment is shown. That is, the battery electrode of the present invention includes a current collector 71 and an active material layer including an active material 73 formed on the surface of the current collector 71, and the active material layer includes the active material. Whisker 75 holding 73 on the surface of current collector 71 is included.

  The material of the current collector 71 is not particularly limited as long as it is an electrically conductive material that can form a foil, but is preferably composed of gold, silver, platinum, aluminum, copper, iron, chromium, nickel, and titanium. One or more selected from the group is possible.

  Further, the current collector can be made thinner than about 15 μm, which is the lower limit of the prior art. This is because in the present invention, the use of a whisker, which will be described later, eliminates the need to use a conductive material and a binder, eliminates the need for a conventional coating process, and does not require tension on the current collector. In the present invention, it is preferable to use a thin film current collector having a lower limit of about 5 μm because of problems in the process. That is, an improvement in energy density and output density can be realized by reducing the thickness of the current collector. The thickness of the current collector is preferably 5 to 20 μm, more preferably 5 to 10 μm.

  The material of the active material 73 is not particularly limited as long as it is a substance capable of occluding and releasing ions, but preferably lithium manganate, lithium nickelate, lithium cobaltate, lithium iron phosphate, lithium titanate, graphite, and hard One or more selected from the group consisting of carbon are possible.

  The average particle diameter (D50) of the active material is not particularly limited, but is preferably 10 nm to 10 μm, more preferably 0.1 to 5 μm. In the present invention, the use of whiskers, which will be described later, eliminates the need for a conductive material, so that the active material can have a smaller particle size and a larger surface area than before, thereby increasing the area of reaction activity. It becomes. Furthermore, since the active material density is increased, the energy density and the output density can be improved. If it is 10 nm or more, it is preferable that the active materials hardly aggregate. In the prior art, as described above, an active material having an average particle diameter of about 10 to 20 μm is used. Therefore, if it is 10 μm or less, the electrode (active material layer) can be made thinner than conventional and energy can be reduced. The output density can be improved while maintaining the density. In addition, as a measurement of an average particle diameter, it is possible to use well-known particle size distribution measuring methods, such as a laser diffraction.

  The thickness of the active material layer is not particularly limited, but is preferably 1 to 20 μm, and more preferably 5 to 10 μm. In the present invention, since the particle diameter of the active material can be reduced because the binder and the conductive material are unnecessary, the active material layer can be thinned to about 1 μm. When the thickness is 1 μm or more, there is no difficulty in the process when the active material is thinly coated on the surface of the current collector. On the other hand, in the prior art, since a 30-60 micrometers thing is used, when it is 30 micrometers or less, it becomes possible to make an electrode thinner than before.

  Therefore, according to the present invention, since the current collector and the active material layer can be made thinner than the conventional technology, it is possible to increase the number of electrode layers per unit volume, while maintaining the energy density. It is possible to improve the power density.

  In the present invention, since a conductive material and a binder are not used as will be described later, it is not necessary to perform a coating process performed in the prior art. Therefore, it is not necessary to apply tension to the current collector, and it is possible to reduce the thickness. Furthermore, the particle diameter of the active material can be reduced, the surface area of the active material can be increased, the number of electrode layers per unit mass and unit volume can be increased, and the density of the active material can be increased. Thus, in the present invention, both the energy density and the power density can be improved.

  The “whisker” used in the present invention refers to acicular crystals formed on the surface of the current collector. Conventionally used conductive material is fixed on the surface of the current collector by being applied to the surface of the current collector together with the binder and the active material, but the whisker 75 is generated and grown from the surface of the current collector. To do. And the said whisker plays the role which hold | maintains on the surface of the said electrical power collector so that the active material mounted on the surface of the electrical power collector may be specifically entangled with a physical effect | action. Furthermore, since the whisker is formed of a conductive material, it plays the same role as the conductive material. Therefore, the conductive material and the binder are not necessary, and a conventional coating method is not necessary. Therefore, as described above, an active material can be placed without applying tension to the current collector, and energy density and output characteristics can be improved by reducing the thickness of the current collector.

  The material of the whisker is not particularly limited as long as it is a conductive material, but preferably from carbon, potassium titanate, titanium carbide, silicon carbide, titanium dioxide, zinc oxide, magnesium oxide, tin dioxide, and indium oxide. One or more selected from the group can be possible. More preferably, it is carbon.

  The diameter of the whisker is preferably 0.01 to 1 μm, more preferably 0.01 to 0.1 μm. In the said range, the said active material can be hold | maintained effectively from the relationship with the particle diameter of the said active material.

  The length of the whisker is preferably 0.1 to 100 μm, more preferably 0.1 to 10 μm. In the above range, the active material can be effectively held and the electrode layers can be effectively laminated, depending on the relationship with the thickness of the active material layer.

  The whisker has an aspect ratio (diameter to length ratio) of preferably 10 to 10,000, more preferably 10 to 100.

  The content ratio of the whisker in the active material layer is preferably more than 0% by mass and 3.5% by mass or less, more preferably 0.5 to 3% with respect to 100% by mass of the active material. 0.5% by mass, more preferably 1.0 to 3.5% by mass.

As described above, according to the present invention, it is possible to produce an electrode comprising 96.5% by mass or more of the electrode constituent material excluding the current collector, and the current collector and the active material constituting the electrode. Since both the material layer and the material layer can be made thinner, it is possible to increase the density and surface area of the active material per volume and mass, and to obtain an electrode excellent in both energy density and power density. .
(Second Embodiment)
In the second embodiment, an example of the battery electrode manufacturing method according to the first embodiment will be described below. However, the technical scope of the battery electrode manufacturing method according to the present invention is not limited to the following, and various modifications can be made by those skilled in the art.

  That is, in the present invention, a step of depositing nickel on the surface of the current collector by electroless plating, a step of placing an active material on the surface of the current collector, a hydrocarbon consisting of only carbon and hydrogen, or oxygen And a step of forming whiskers made of carbon from the nickel as a starting point by heat-treating the current collector in an atmosphere of containing hydrocarbon.

  2 to 4 are cross-sectional views showing each stage of the manufacturing method of the present embodiment.

  In the first stage (FIG. 2), electroless plating is performed to deposit nickel 77 as a whisker base point on the surface of the current collector 71. The nickel 77 can be replaced with, for example, cobalt or a group 8 element, but is preferably nickel. The density of the nickel 77 is not particularly limited, that is, there may be a gap between the nickel 77, while the nickel 77 may be formed without a gap. Further, the nickel 77 may have a single layer structure or a multilayer structure as a whole. Moreover, although the said electroless plating can be performed by a well-known method, an example of the electroless nickel plating which precipitates nickel on the collector surface below is given. However, the present invention is not limited to the following.

  First, activation processing is performed as preprocessing. When tin salt or the like is added to hydrochloric acid and then the current collector is immersed, metallic tin is adsorbed on the surface of the current collector in the solution. Subsequently, when a palladium salt is added to the solution, metallic palladium is adsorbed on the surface of the current collector by an oxidation-reduction reaction. Metallic palladium has catalytic activity and becomes the nucleus for subsequent nickel deposition.

  Subsequently, electroless nickel plating is performed. After adjusting the pH of the solution, a nickel salt and a reducing agent (for example, sodium hypophosphite) are added. Metal palladium is oxidized by the reducing agent, and nickel ions are reduced to form metal nickel, which is deposited on the surface of the current collector.

  In the second stage (FIG. 3), the active material 73 is placed on the surface of the current collector 71, but the conventional coating method described above need not be performed. Specifically, the active material 73 can be placed on the surface of the current collector 71 by a method such as screen meshing, spray coating, or inkjet coating.

  In the third stage (FIG. 4), the current collector is heat-treated in an atmosphere of a hydrocarbon containing only carbon and hydrogen or a hydrocarbon containing oxygen. Thereby, whisker 75 made of carbon (hereinafter also referred to as carbon whisker) is grown from the metallic nickel 77 deposited on the surface of the current collector 71 in the first step. In the heat treatment, the hydrocarbon composed of only carbon and hydrogen includes all compounds composed of only carbon and hydrogen, and is not limited to the following, but includes, for example, ethylene, acetylene and methane. Further, the oxygen-containing hydrocarbon includes all compounds composed of carbon, hydrogen and oxygen, and is not limited to the following, but examples include alcohols, ethers, aldehydes and ketones, and more specifically. Examples include methanol, ethanol and diethyl ether. The heat treatment is preferably performed in a hydrocarbon atmosphere composed of only carbon and hydrogen, and more preferably in an ethylene atmosphere. Moreover, about the conditions of the said heat processing, Preferably, temperature is 450 to 650 degreeC, and time is 30 minutes-60 minutes. Moreover, the density | concentration of the said hydrocarbon is 10-50 volume%, More preferably, it is 20-30 volume%.

Since the carbon whisker 75 formed on the surface of the current collector 71 has conductivity, the carbon whisker 75 has a function as a conductive material in a conventional electrode, and the active material 73 is transferred to the current collector by physical action. Since it has the function to hold | maintain on the surface of 71, it can also play the role as a binder in a conventional type electrode. Therefore, the binder and the conductive material are unnecessary, and a battery electrode excellent in both energy density and output density can be obtained.
(Third embodiment)
In 3rd Embodiment, a secondary battery is comprised using the manufacturing method of the battery electrode by 1st Embodiment, and the battery electrode by 2nd Embodiment. That is, a third aspect of the present invention is a secondary battery including one or more single battery layers in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order, and at least one of the positive electrode and the negative electrode is a first battery. It is a battery electrode obtained by the battery electrode of the embodiment or the battery electrode obtained by the manufacturing method of the second embodiment. The electrode of the present invention can be applied to any of a positive electrode, a negative electrode, and a bipolar electrode. A secondary battery including the electrode of the present invention as at least one electrode belongs to the technical scope of the present invention. However, preferably, all of the electrodes constituting the secondary battery can be the electrodes of the present invention. Further, the secondary battery is not particularly limited, but a lithium ion secondary battery is preferable. By adopting such a configuration, it is possible to effectively improve the output characteristics of the secondary battery.

  The battery of the present invention may be a bipolar lithium ion secondary battery (hereinafter also referred to as “bipolar battery”). FIG. 5 is a cross-sectional view showing a lithium ion secondary battery of the present invention which is a bipolar battery. Hereinafter, the bipolar battery shown in FIG. 5 will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  The bipolar battery 10 of this embodiment shown in FIG. 5 has a structure in which a substantially rectangular battery element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior.

  As shown in FIG. 5, the battery element 21 of the bipolar battery 10 of this embodiment includes a plurality of bipolar electrodes in which a positive electrode active material layer 13 and a negative electrode active material layer 15 are formed on each surface of a current collector 11. Have one. Each bipolar electrode is stacked via an electrolyte layer 17 to form a battery element 21. At this time, each bipolar electrode and electrolyte layer are arranged such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. 17 are stacked.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar battery 10 has a configuration in which the single battery layers 19 are stacked. In addition, an insulating layer 31 is provided on the outer periphery of the unit cell layer 19 to insulate between the adjacent current collectors 11. The current collector (outermost layer current collector) (11a, 11b) located in the outermost layer of the battery element 21 has a positive electrode active material layer 13 (positive electrode side outermost layer current collector 11a) or a negative electrode only on one side. One of the active material layers 15 (negative electrode side outermost layer current collector 11b) is formed.

  Further, in the bipolar battery 10 shown in FIG. 5, the positive electrode side outermost layer current collector 11 a extends to become the positive electrode tab 25, which is led out from the laminate sheet 29 that is an exterior. On the other hand, the negative electrode side outermost layer current collector 11 b extends to become the negative electrode tab 27, which is similarly derived from the laminate sheet 29.

  Hereinafter, members constituting the bipolar battery 10 of the present embodiment will be briefly described. However, since the components constituting the electrode are as described above, the description thereof is omitted here. Further, the technical scope of the present invention is not limited to the following forms, and conventionally known forms can be similarly adopted.

[Electrolyte layer]
A liquid electrolyte or a polymer electrolyte can be used as the electrolyte constituting the electrolyte layer 17.

  The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent that can be used as the plasticizer include, but are not limited to, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). The supporting salt (lithium salt) is not limited to the following, and examples thereof include compounds that can be added to the active material layer of the electrode, such as LiBETI.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and an intrinsic polymer electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. Examples of the ion conductive polymer used as the matrix polymer include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such a polyalkylene oxide polymer, for example, an electrolyte salt such as a lithium salt can be well dissolved.

  When the electrolyte layer 17 is composed of a liquid electrolyte or a gel electrolyte, a separator may be used for the electrolyte layer 17. Specific examples of the separator include, but are not limited to, a microporous film made of polyolefin such as polyethylene or polypropylene.

  The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer 17 is composed of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

  The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Insulation layer]
In the bipolar battery 10, an insulating layer 31 is usually provided around each single battery layer 19. The insulating layer 31 is provided for the purpose of preventing the adjacent current collectors 11 in the battery from contacting each other or causing a short circuit due to a slight irregularity of the end of the unit cell layer 19 in the battery element 21. It is done. The installation of such an insulating layer 31 ensures long-term reliability and safety, and can provide a high-quality bipolar battery 10.

  The insulating layer 31 only needs to have insulating properties, sealing properties against falling off of the solid electrolyte, sealing properties against moisture permeation from the outside (sealing properties), heat resistance under the battery operating temperature, etc. For example, urethane resin, epoxy resin, polyethylene resin, polypropylene resin, polyimide resin, rubber and the like can be used. Preferably, a urethane resin or an epoxy resin can be used from the viewpoints of corrosion resistance, chemical resistance, ease of production (film forming property), economy, and the like.

[tab]
In the bipolar battery 10, the tabs (the positive electrode tab 25 and the negative electrode tab 27) electrically connected to the outermost current collector (11 a, 11 b) are taken out of the exterior for the purpose of taking out the current outside the battery. . Specifically, a positive electrode tab 25 electrically connected to the positive electrode outermost layer current collector 11a and a negative electrode tab 27 electrically connected to the negative electrode outermost layer current collector 11b are provided outside the exterior. It is taken out.

  The material of the tabs (the positive electrode tab 25 and the negative electrode tab 27) is not particularly limited, and a known material conventionally used as a tab for a bipolar battery can be used. Examples thereof include aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof. Note that the same material may be used for the positive electrode tab 25 and the negative electrode tab 27, or different materials may be used. As in the present embodiment, the outermost layer current collectors (11a, 11b) may be extended to form tabs (25, 27), or a separately prepared tab may be connected to the outermost layer current collector. Good.

[Exterior]
In the bipolar battery 10, the battery element 21 is preferably housed in an exterior such as a laminate sheet 29 in order to prevent external impact and environmental degradation during use. The exterior is not particularly limited, and a conventionally known exterior can be used. A polymer-metal composite laminate sheet or the like excellent in thermal conductivity can be preferably used in that heat can be efficiently transferred from a heat source of an automobile and the inside of the battery can be rapidly heated to the battery operating temperature.
(Fourth embodiment)
In the fourth embodiment, a plurality of the secondary batteries of the third embodiment are connected in parallel and / or in series to constitute an assembled battery.

  FIG. 6 is a perspective view showing the assembled battery of the present embodiment.

  As shown in FIG. 6, the assembled battery 40 is configured by connecting a plurality of bipolar batteries described in the third embodiment. Each bipolar battery 10 is connected by connecting the positive electrode tab 25 and the negative electrode tab 27 of each bipolar battery 10 using a bus bar. On one side surface of the assembled battery 40, electrode terminals (42, 43) are provided as electrodes of the entire assembled battery 40.

  A connection method in particular when connecting the some bipolar battery 10 which comprises the assembled battery 40 is not restrict | limited, A conventionally well-known method can be employ | adopted suitably. For example, a technique using welding such as ultrasonic welding or spot welding, or a technique of fixing using rivets, caulking, or the like can be employed. According to such a connection method, the long-term reliability of the assembled battery 40 can be improved.

  According to the assembled battery 40 of this embodiment, since each bipolar battery 10 constituting the assembled battery 40 is excellent in output characteristics, an assembled battery excellent in output characteristics can be provided.

  The bipolar batteries 10 constituting the assembled battery 40 may be connected in parallel to each other, or may be connected in series, or a combination of series connection and parallel connection. May be.

(Fifth embodiment)
In the fifth embodiment, the bipolar battery 10 of the third embodiment or the assembled battery 40 of the fourth embodiment is mounted as a motor driving power source to constitute a vehicle. As a vehicle using the bipolar battery 10 or the assembled battery 40 as a motor power source, for example, a complete electric vehicle not using gasoline, a hybrid vehicle such as a series hybrid vehicle or a parallel hybrid vehicle, and a fuel cell vehicle, a wheel motor is used. A car driven by

  For reference, FIG. 7 shows a schematic diagram of an automobile 50 on which the assembled battery 40 is mounted. The assembled battery 40 mounted on the automobile 50 has the characteristics as described above. For this reason, the automobile 50 equipped with the assembled battery 40 is excellent in output characteristics.

  As described above, some preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications, omissions, and additions can be made by those skilled in the art. . For example, in the above-described third embodiment, a bipolar lithium ion secondary battery (bipolar battery) has been described as an example. However, the technical scope of the battery of the present invention is not limited to a bipolar battery. For example, it may be a lithium ion secondary battery that is not a bipolar type. For reference, FIG. 8 is a cross-sectional view showing an outline of a lithium ion secondary battery 60 that is not a bipolar type.

  The effects of the battery electrode according to the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

<Example 1>
[Pretreatment process]
Carbon whiskers were prepared on the surface of a current collector made of 20 μm thick aluminum by the following method. The method is shown below.

  First, an activation process was performed. 30 g of stannous chloride and 30 cc of concentrated hydrochloric acid were diluted with distilled water to 1 liter, and a current collector made of aluminum having a thickness of 20 μm was immersed in this solution for 1 minute, so that tin was deposited on the surface of the current collector. Adsorbed. Next, 0.1 g of palladium chloride and 2 ml of concentrated hydrochloric acid were diluted with distilled water to 1 liter, and the current collector was immersed in this solution at 40 ° C. for 1 minute.

  Subsequently, electroless nickel plating was performed. 20 g of nickel sulfate, 10 g of sodium hypophosphite, 5 g of sodium acetate, 5 g of sodium citrate, and 3 cc of lactic acid were adjusted to 1 liter. Then, it adjusted with hydrochloric acid and sodium hydroxide so that pH might be set to 6. The current collector was immersed in this solution at 60 ° C. for 1 minute to deposit metallic nickel on the surface of the current collector.

Subsequently, a lithium manganate positive electrode active material having a particle diameter of 1 μm is placed on the surface of the current collector so as to be 7 mg / cm ² using a screen mesh, and heat treatment is performed in an ethylene gas atmosphere at 600 ° C. for 30 minutes. It was. As a result, whisker-like carbon was generated from the metallic nickel on the surface of the current collector, and the active material was retained on the surface of the current collector. Generation of such carbon whiskers increased the electrode mass per unit area by 0.1 mg / cm ² .

<Example 2>
Carbon whiskers were formed on the surface of a current collector made of aluminum having a thickness of 10 μm. The conditions were the same as in Example 1 except for the thickness of the current collector.

<Example 3>
Carbon whiskers were formed on the surface of a current collector made of aluminum having a thickness of 5 μm. The conditions were the same as in Example 1 except for the thickness of the current collector.

<Example 4>
The same conditions as in Example 1 were followed except that a lithium manganate positive electrode active material having a particle diameter of 1 μm was placed on the surface of a current collector made of aluminum having a thickness of 5 μm so as to be 5 mg / cm ² . Generation of such carbon whiskers increased the electrode mass per unit area by 0.1 mg / cm ² .

<Example 5>
The same conditions as in Example 1 were performed except that a lithium manganate positive electrode active material having a particle diameter of 1 μm was placed on the surface of a current collector made of aluminum having a thickness of 5 μm so as to be 3 mg / cm ² . Generation of such carbon whiskers increased the electrode mass per unit area by 0.1 mg / cm ² .

<Comparative example>
[Creation of positive electrode]
First, a positive electrode ink was prepared. 85 g of lithium manganate having a particle diameter of 1 μm as a positive electrode active material, 5 g of PVdF as a binder, and 10 g of graphite as a conductive material were weighed and dispersed by adding NMP to adjust the viscosity to 4,000 cPs.

Subsequently, the positive electrode ink prepared above was applied to the surface of a current collector made of aluminum having a thickness of 20 μm so as to be 7 mg / cm ² by a bar coater.

<Experimental example>
[Create coin cell]
Using the positive electrode prepared in each of the above examples and comparative examples, a coin cell was prepared by the following method.

  First, the positive electrode prepared in each of the above Examples and Comparative Examples was punched out with a diameter of 16 mm to obtain a coin cell positive electrode. For the negative electrode, an active material obtained by punching metallic lithium into φ16 mm was used. A 25 μm polypropylene microporous membrane was used as the separator. As the electrolytic solution, one obtained by dissolving 1 mol of lithium hexafluorophosphate in a solution obtained by mixing ethylene carbonate and diethyl carbonate was used. A coin cell was prepared using the positive electrode, the negative electrode, the separator, and the electrolytic solution. A specific method for manufacturing the coin cell is omitted because a known method is used.

[Evaluation of battery characteristics of coin cell]
Using the coin cell produced in each of the above examples and comparative examples, a charge / discharge test was performed by the following method.

(Measurement of discharge capacity per mass and volume of active material)
The charge / discharge test of the coin cell of each of the above examples and comparative examples was performed. The temperature during the test is 25 ° C. After charging to 4.2 V at a constant current of 1 mA, constant voltage charging was performed until the current was reduced to 0.01 mA while holding 4.2 V. Thereafter, discharging was performed at a constant current of 1 mA up to 2.5V. The discharge capacity (energy density) at this time was defined as the initial discharge capacity of each coin cell.

(Measurement of rate characteristics)
After charging to 4.2 V at a constant current of 1 mA, constant voltage charging was performed until the current was reduced to 0.01 mA while holding 4.2 V. Thereafter, discharge was performed at a constant current having a current value 5 times the initial discharge capacity. The ratio of the discharge capacity to the initial discharge capacity at this time was defined as the 5C discharge characteristic of each coin cell.

  Table 1 shows the initial discharge capacity and 5C discharge characteristics of the coin cells of the examples and comparative examples. The initial discharge capacity was proportional to the amount of the positive electrode active material. Examples 1 to 3 and the comparative example had substantially the same discharge capacity. In Examples 4 and 5, since the amount of the positive electrode active material was small as compared with other cases, the initial discharge capacity was also smaller. As for the 5C discharge characteristics, in Examples 1 to 3 and Comparative Examples, Examples 1 to 3 were slightly better than Comparative Examples. This is considered to be because the electrodes in Examples 1 to 3 did not contain a binder and a conductive material, so that the electrodes were slightly thinned (see Table 2 above). For Examples 4 and 5, 5C discharge characteristics superior to those in other cases were obtained. This is presumably because the amount of the positive electrode active material is smaller, so that the electrode is made much thinner than in other cases, and thereby lithium is smoothly diffused.

  In Table 3 above, the discharge capacity per unit mass (mass energy density) and the discharge capacity per unit volume (volume energy) of the positive electrode (active material, current collector, binder, and conductive material) of the coin cell of each example and comparative example. Density). In Example 1 and the comparative example, since the thickness of the current collector and the amount of the active material were almost the same, the values were almost the same. Since the current collectors of Examples 2 and 3 are thinner than those of Example 1, the discharge capacity per mass and per volume are larger than those of Example 1. In Examples 4 and 5, while the thickness of the current collector is the same as that of Example 3, the amount of the active material is reduced. Therefore, the discharge capacity per mass and per volume is lower than in Example 3.

  From the above results, it was found that by using the present invention, excellent rate discharge characteristics can be obtained without reducing the discharge capacity per mass and per volume compared to the comparative example, that is, the conventional technique. Therefore, it was confirmed that the battery using the electrode according to the present invention was excellent in rate characteristics and as a result, excellent in output characteristics as compared with a battery using a conventional binder and conductive material.

  The battery electrode of the present invention is suitably used in a secondary battery used as a high output, such as a motor driving power source or a power tool power source for automobiles.

It is sectional drawing of the battery electrode of 1st Embodiment. It is sectional drawing which shows one step of the manufacturing method of the battery electrode by 2nd Embodiment. It is sectional drawing which shows one step of the manufacturing method of the battery electrode by 2nd Embodiment. It is sectional drawing which shows one step of the manufacturing method of the battery electrode by 2nd Embodiment. It is sectional drawing which shows preferable one Embodiment of the bipolar battery of 3rd Embodiment. It is a perspective view which shows the assembled battery of 4th Embodiment. It is the schematic of the motor vehicle of 5th Embodiment carrying the assembled battery of 4th Embodiment. It is sectional drawing which shows the outline | summary of the lithium ion secondary battery which is not a bipolar type.

Explanation of symbols

10 Bipolar battery,
11 Current collector,
11a Positive electrode side outermost layer current collector,
11b The negative electrode side outermost layer current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 battery elements,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet,
31 insulating layer,
33 positive electrode current collector,
35 negative electrode current collector,
40 battery packs,
42, 43 electrode terminals,
50 cars,
60 Lithium ion secondary battery that is not bipolar,
71 current collector,
73 active material,
75 (carbon) whisker,
77 Metallic nickel.

Claims (11)

A current collector,
An active material layer containing an active material formed on the surface of the current collector;
A battery electrode comprising:
The battery electrode, wherein the active material layer includes whiskers that hold the active material on a surface of the current collector.   The battery electrode according to claim 1, wherein the whisker has a diameter of 0.01 to 1 μm.   The battery electrode according to claim 1, wherein a length of the whisker is 0.1 to 100 μm.   The battery electrode according to any one of claims 1 to 3, wherein the whisker has an aspect ratio of 10 to 10,000.   The whisker material is at least one selected from the group consisting of carbon, potassium titanate, titanium carbide, silicon carbide, titanium dioxide, zinc oxide, magnesium oxide, tin dioxide, and indium oxide, The battery electrode according to any one of claims 1 to 4.   The material for the current collector is at least one selected from the group consisting of gold, silver, platinum, aluminum, copper, iron, chromium, nickel, and titanium. The battery electrode according to claim 1.   The material of the active material is at least one selected from lithium manganate, lithium nickelate, lithium cobaltate, lithium iron phosphate, lithium titanate, graphite, and hard carbon. The battery electrode according to any one of -6. Depositing nickel on the surface of the current collector by electroless plating;
Placing an active material on the surface of the current collector;
Forming a whisker made of carbon based on the nickel by heat-treating the current collector in a hydrocarbon atmosphere containing only carbon and hydrogen, or a hydrocarbon containing oxygen; and
The manufacturing method of the electrode for batteries containing this. A secondary battery including one or more single battery layers in which a positive electrode, an electrolyte layer, and a negative electrode are laminated in this order,
At least one of the positive electrode or the negative electrode is the battery electrode according to any one of claims 1 to 7, or the battery electrode obtained by the manufacturing method according to claim 8. , Secondary battery.   An assembled battery using the secondary battery according to claim 9.   A vehicle, wherein the secondary battery according to claim 9 or the assembled battery according to claim 10 is mounted as a power source for driving a motor.

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