JP2015190039A - Method for producing porous anodic oxidation film and the porous anodic oxidation film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a porous anodic oxidation film which is dense, crystalline and suitably usable as an electrode (particularly, the electrode of an Li secondary battery), and a porous anodic oxidation film.SOLUTION: Provided is a method for producing a porous anodic oxidation film characterized in that a Ti substrate is anodically oxidized under the voltage below 100 V using a nitric acid based electrolytic solution, and also provided is a method for producing a multi-layer porous anodic oxidation film characterized in that a second anode oxidation step with an ammonium nitrate solution is performed after the first anode oxidation step with a sulfuric acid solution or an ammonium sulfate solution.

Description

  The present invention relates to a method for producing a porous anodized film and a porous anodized film.

  Secondary batteries have been used in various electronic devices in various sizes and shapes according to the use because electrical energy can be stored and released repeatedly. Due to the remarkable development of portable electronic devices in recent years and the necessity of effective use of electric energy, it is required to increase the capacity and power of lithium ion secondary batteries.

The lithium ion secondary battery having the highest energy density at present has the following characteristics as compared with other secondary batteries.
(1) High energy density (the battery itself can be made smaller and lighter)
(2) High operating voltage (Large output can be obtained with a small number of units, enabling downsizing and weight reduction of equipment)
(3) No memory effect (additional charging is possible)
(4) High safety (strong overcharge, high thermal stability)
(5) Lithium ion secondary batteries are attracting attention because of their long life. For this reason, it is highly possible that the needs of the market will be satisfied by further improving the performance of the lithium ion secondary battery, and so far, development research has been carried out at companies and universities in the world.

Therefore, the required high-performance battery is difficult to achieve with conventional material technology, and therefore, innovation in power storage technology is expected. In particular, against the background of recent advances in nanoscience and nanotechnology, there is an interest in developing large-capacity, high-power electrode materials based on precise nanostructure control of electrochemically active materials. As an example, research has been conducted in which a nanoporous titania (TiO ₂ ) film is formed by anodic oxidation and applied as an electrode material such as a photocatalytic material, a solar battery, or a Li battery.
As described above, research has been conducted in which a nanoporous titania (TiO ₂ ) film is formed by anodic oxidation and applied as an electrode material such as a photocatalytic material, a solar battery, or a Li battery (Patent Documents 1-4 and Non-Patent Document 1). ).

Japanese Patent No. 5197766 JP 2010-108904 A JP 2006-89842 A JP 2005-272885 A

SZ Chu *, S. Inoue, K. Wada, S. Hishida, K. Kurashima, “Self-Organized Nanoporous Anodic Titania Films and Ordered Quantum Titania Nanodots / Nanorodson Glass”, Advanced Functional Materials, 15 (8): 1343-1349, 2005.

In the prior art, an organic electrolyte containing a highly corrosive fluoride ion is mainly used to produce a nanoporous or nanotube-like TiO ₂ film, which is a semiconductor in addition to adversely affecting the environment. There is a problem that the conductivity (10 ⁻¹¹ −10 ⁻¹² Ω ⁻¹ m ⁻¹ ) of the TiO ₂ film is low. On the other hand, titanium nitride (TiN) has excellent conductivity (2.5 × 10 ⁶ Ω ⁻¹ m ⁻¹ ), and is therefore often used as a conductive aid in various electrodes. Since high temperature sintering is required, the manufacturing cost is high.
Also, a dense film has not been obtained. That is, the surface is powdery, and even though it can be used as a catalyst, a dense film that can be used as a battery electrode has not been obtained.

Furthermore, a crystalline film is not obtained.
Therefore, in the present invention, in order to improve the conductivity of the titania anodic oxide film, aiming at a new electrode material for a lithium ion secondary battery, the anodic oxidation of the Ti plate is performed using a nitric acid-based electrolyte, and nitrogen is contained in the film. The purpose was to create a TiO ₂ —TiN composite film.
An object of the present invention is to provide a method for producing a porous anodic oxide film that is dense and crystalline and can be suitably used as an electrode (particularly, an electrode of a lithium ion secondary battery) and a porous anodic oxide film.

  The invention according to claim 1 is a method for producing a porous anodic oxide film, characterized by anodizing a Ti substrate using a nitric acid-based electrolyte under a voltage of less than 100V.

  The invention according to claim 2 is the method for producing a porous anodized film according to claim 1, wherein the pH of the electrolytic solution is 11 or less.

  The invention according to claim 3 is the method for producing a porous anodized film according to claim 1 or 2, wherein the voltage is 5-35V.

The invention according to claim 4 is the porous anodized film according to any one of claims 1 to 3, wherein the current density during the anodization is 3.0 to 5.0 mAcm ^-2 . It is a manufacturing method.

  The invention according to claim 5 is the method for producing a porous anodic oxide film according to any one of claims 1 to 4, wherein the nitric acid-based electrolytic solution is an ammonium nitrate solution.

  The invention according to claim 6 is a method for producing a porous anodic oxide film, characterized by anodizing a Ti substrate under a voltage of 70 V or more using a sulfuric acid electrolyte.

The invention according to claim 7 is the method for producing a porous anodized film according to claim 6, wherein the voltage is 100 V or more.
The invention according to claim 8 is the method for producing a porous anodized film according to claim 6, wherein the pH of the electrolytic solution is 11 or less.

  The invention according to claim 9 is the method for producing a porous anodic oxide film according to any one of claims 6 to 8, wherein the sulfuric acid electrolyte is a sulfuric acid solution or an ammonium sulfate solution.

  The invention according to claim 10 is the production of a multilayer porous anodic oxide film characterized by performing a second anodizing step with a nitric acid solution or an ammonium nitrate solution after a first anodizing step with a sulfuric acid solution or an ammonium sulfate solution. Is the method.

  The invention according to claim 11 is characterized in that a sulfuric acid solution is used in the first anodic oxidation step and ammonium nitrate is used in the second anodic oxidation step. Is the method.

  The invention according to claim 12 is characterized in that an ammonium sulfate solution is used in the first anodizing step and ammonium nitrate is used in the second anodizing step. Is the method.

  The invention according to claim 13 is a porous anodized film formed on a Ti substrate with an average pore diameter of about 10-30 nm and a distance between pores of 80 nm or more.

The invention according to claim 14 is the anodized film according to claim 13, wherein the anodized film is a composite oxide film of TiO ₂ —TiN.

The invention according to claim 15 is a porous anodized film formed on a Ti substrate with an average pore diameter of φ50 to 150 nm and a distance between pores of 250 nm or more.
The film thickness is preferably 450-500 nm.

  In the invention according to claim 16, a film having an average pore diameter of about 10-30 nm and a distance between pores of 80 nm or more and a film having an average pore diameter of 50-150 nm and a distance between pores of 250 nm or more are formed on a Ti substrate. It is a porous anodic oxide film characterized by being made.

  The invention according to claim 17 is the porous anodized film according to any one of claims 13 to 16, wherein the film is crystalline.

  The invention according to claim 18 is an electrode comprising the porous anodic oxide film according to any one of claims 13 to 17.

  The invention according to claim 19 is the electrode according to claim 18, wherein the electrode is an electrode for a lithium ion secondary battery.

  An invention according to claim 20 is a battery having the electrode according to claim 17 or 18.

a. The prior art used an electrolytic solution containing nitrate ions. In the present invention, an acidic solution containing ammonia ions is used as an electrolytic solution. Moreover, pH is adjusted.
b. The prior art is a particulate titanium oxide or sponge-like film. The present invention is an anodized film having a porous structure composed of an assembly of nano-sized cylindrical pore cells. The size of the pore is 5 nm to 500 nm in diameter, and can be controlled by the electrolytic solution and the anodic oxidation conditions.
c. The prior art is a technique for forming titanium oxide particles within 10 V or more, 100 V or less, 30 seconds or more, and 60 minutes. In the present invention, a composite coating of titanium oxide and titanium nitride can be produced by treating the anodic oxidation voltage from 5 V to 600 V (the maximum voltage of the DC power supply) for 10 seconds or longer. Moreover, if it is 10V or more, the porous composite membrane | film | coat which has a nanopore will be obtained. Furthermore, since the thickness of the porous film is proportional to the anodizing time or current density / voltage, there is no limit on the film thickness.

d. In the prior art, it was necessary to perform crystallization by heat treatment for 1 minute to 24 hours in a temperature range of 200 ° C. to 750 ° C. after anodization. In the present invention, when the voltage is 5 V or higher (preferably 15 V or higher, more preferably 20 V or higher), a crystalline anodized film made of (anatase type) titanium oxide can be obtained, and thus heat treatment is unnecessary. The upper limit may be 35V.
e. The prior art has a pH of 12 to 15. In the present invention, the pH of the electrolytic solution can be processed in a wide range from 0 to 11.
f. When nitrate ions and ammonia ions coexist, a composite oxide film with better adhesion and uniformity can be formed by two-step anodic oxidation than when only nitrate ions are included.
g. In the first step, a thin porous titanium oxide film is formed by anodization in sulfuric acid, oxalic acid, phosphoric acid, organic acids and their mixtures, and the field filter is used during the next anodization. The starting point of the pore can be derived.

The present invention also has the following effects.
-A porous titanium oxide film having nanopores is prepared.
-A thick porous titanium oxide film having good adhesion to the substrate can be produced.
-Improve the conductivity of the titanium oxide film by introducing highly conductive titanium nitride into the titanium oxide of the semiconductor.
A titanium oxide film can be formed by anodic oxidation, and titanium nitride can also be formed and dispersed throughout the film to form and produce a composite porous film of titanium oxide and titanium nitride.
-A crystalline titanium oxide film can be formed directly depending on the conditions of anodization. (No heat treatment required)
-Nitriding can be performed at a low temperature by a wet method. The content (or nitridation rate) of titanium nitride can be controlled by the composition and concentration of the electrolytic solution, the solution temperature, operating conditions, and the like. (In the past, high temperature treatment at 700 to 900 ° C. in an ammonia salt bath is common.)
In general, the content of titanium nitride increases as the concentration of the electrolytic solution (ammonium nitrate) increases, and the crystallinity increases as the applied voltage increases. Further, since the pore size (diameter) of the porous film is proportional to the temperature, voltage, and current density of the electrolytic solution, these may be appropriately controlled depending on the application.

Typical porous anodized film structure Schematic diagram of experimental equipment Diagram showing how to make a bipolar pouch cell It is a figure which shows the test piece after anodic oxidation of 1 h and 5 degreeC by each constant voltage using 0.05M ammonium nitrate solution. Surface FE-SEM images (a), (b) 15 V, (c), (d) 20 V, (e) of the film formed after anodic oxidation at 5 ° C. for 1 h at each constant voltage using 0.05 M ammonium nitrate solution, (F) 25V XPS spectra (a), (b) 15 V, (c), (d) 20 V, (e), (f) of the film formed after anodic oxidation at 5 ° C. for 1 h at each constant voltage using 0.05 M ammonium nitrate solution 25V Surface FE-SEM images (a), (b) 1 ° C., (c), (d) of the film formed after anodic oxidation at a constant current density of 3.0 mAcm ⁻² , 1 h using 0.05M ammonium nitrate solution at each temperature 5 ℃ Surface FE-SEM image of film formed after anodic oxidation at 10 ° C., constant current density 3.0 mAcm ⁻² , 1 h using 0.05 M ammonium nitrate solution Surface and cross-section FE-SEM images (a), (b) 1 ° C., (c) of the film formed after anodic oxidation at a constant current density of 5.0 mAcm ⁻² , 1 h at each temperature using 0.05M ammonium nitrate solution (D) 5 ° C, (e), (f), (c) film cross section XPS spectrum of film formed after anodic oxidation at 5.0 mAcm ^-2 , 1h, 5 ° C using 0.05M ammonium nitrate solution Sections of the film formed after anodic oxidation at 5.0 mA cm ⁻² , 1 h, 5 ° C. using 0.05 M ammonium nitrate solution (a), (b) TEM image (c), (d) Electron diffraction diffraction spot diagram EDS spectrum of film formed after anodic oxidation at 5.0 mAcm ^-2 , 1h, 5 ° C using 0.05M ammonium nitrate solution (a) Overall (b) Oxide film (c) Substrate Surface FE-SEM images (a), (b) 40 V, (c), (d) 50 V, (e), (f) of the film formed after anodic oxidation for 20 min at each voltage and room temperature using 10 vol% sulfuric acid solution 60V Surface FE-SEM images (a), (b) 70V, (c), (d) 80V of the film formed after anodic oxidation for 20 minutes at room temperature and each voltage using 10 vol% sulfuric acid solution Surface FE-SEM images (a), (b) 90 V, (c), (d) 100 V of the film formed after anodic oxidation for 20 min at each voltage and room temperature using 10 vol% sulfuric acid solution Specimen after anodization for 20 min at 10 m% sulfuric acid solution at each voltage at room temperature XPS spectrum of a film formed after anodization of 20 min at a voltage and room temperature using 10 vol% sulfuric acid solution Surface FE-SEM images (a), (b) 15 V, (c), (c), (d) 20 V, (e), (f) of the film formed after anodic oxidation for 1 h at each voltage and room temperature using 0.5 M ammonium sulfate solution ) 25V Surface FE-SEM images (a), (b) 0.5M, (c), (d) 2M of the film formed after anodic oxidation at 100 V, room temperature for 1 h using an ammonium sulfate solution XPS spectrum of film formed after anodic oxidation at 100V and room temperature for 1h using 2M ammonium sulfate solution Cross-sections of films (a), (b) TEM images (c), (d) Electron diffraction diffraction spots generated after anodic oxidation at 100 V and room temperature for 1 h using a 2M ammonium sulfate solution EDS spectrum of the cross section of the film formed after anodic oxidation at 100 V and room temperature for 1 h using 2 M ammonium sulfate solution (b) Oxide film (c) Substrate Surface FE-SEM images (a), (b) 15 V, (c), (d) 20 V, (e), (f) of the film formed after anodic oxidation for 1 h at 5 ° C. with 10 vol% ammonia water ) 25V XPS spectrum of the film formed after anodic oxidation for 1 h at 5 ° C with 10 vol% ammonia water Current density-time curve (a) First stage (b) Second stage External view of the film formed after anodic oxidation using sulfuric acid solution in the first stage and ammonium nitrate solution in the second stage Surface FE-SEM image of the film formed after two-step anodic oxidation First step: 10 vol% sulfuric acid solution, 20 min, room temperature (a), (b) 20 V, (c), (d) 50 V, (e), (f ) 100V 2nd stage: 0.05M ammonium nitrate solution, 25V, 1h, 5 ° C Cross section of the film formed after anodic oxidation of sulfuric acid 100V, 20min in the first stage, ammonium nitrate 25V, 1h in the second stage An EDS spectrum of a film formed after anodization of sulfuric acid 100 V for 20 min in the first stage, ammonium nitrate 25 V in the second stage, and 1 h. (A) Overall (b) Film formed in the first stage EDS spectrum of the film formed after anodic oxidation of sulfuric acid 100V, 20min in the first stage, ammonium nitrate 25V, 1h in the second stage (a) Film formed in the second stage (b) Substrate XPS spectrum of the film formed after anodic oxidation of sulfuric acid 100V, 20min in the first stage, ammonium nitrate 25V, 1h in the second stage Film (a), (b) surface, (c) Cross section formed after anodic oxidation of ammonium sulfate 100V, 1h in the first stage, ammonium nitrate 25V, 1h in the second stage XRD pattern of film formed by two-step anodic oxidation (a) First stage: sulfuric acid solution, second stage: ammonium nitrate solution (b) First stage: ammonium sulfate solution, second stage: ammonium nitrate solution Battery characteristics of TiO ₂ -TiN composite film (450 nm) produced by two-stage anodic oxidation using sulfuric acid solution in the first stage and ammonium nitrate solution in the second stage (a) charge / discharge curve (b) cycle characteristics Battery characteristics of TiO ₂ -TiN composite film (500 nm) produced by two-stage anodic oxidation using ammonium sulfate in the first stage and ammonium nitrate in the second stage (a) charge / discharge curve (b) cycle characteristics Battery characteristics of TiO ₂ film produced by anodic oxidation using sulfuric acid solution (a) Charging / discharging curve (b) Cycle characteristics

The form for implementing this invention is demonstrated below.
1-2 Anodic oxidation 1-2-1 Anodic oxidation of first type valve metal There are two types of metal, transition metal and non-transition metal. On the other hand, from the viewpoint of metal dielectric properties, there is a classification of valve metal. The term “valve” means a metal having a valve action. To be precise, the oxide film formed on the surface of the metal has such a characteristic that current flows only in one direction and is difficult to flow in the opposite direction. In other words, it is an oxide film with a rectifying action.

  Aluminum has long been a representative of valve metals, but niobium, tantalum, titanium, zirconium, hafnium, rare earth elements, etc. were also classified as valve metals (first type). Sometimes zinc, copper, cobalt, nickel, chromium, manganese, molybdenum, tungsten, etc. are also classified as valve metals (second type). However, in order for the oxide film formed on the surface of the metal to have a rectifying action, it strongly depends on the type of electrolytic solution that forms the oxide film. Depending on whether the liquid is acidified, alkaline, aqueous or non-aqueous, or molten salt, its properties differ significantly.

  The metal that can be anodized is an oxide that forms an electrically insulating barrier film at the beginning of oxidation. That is, the oxide film grows only when an oxide that has a very low electronic conductivity and exhibits a slight ionic conductivity under a high electric field.

The anodic oxide film handled here includes a barrier film and a porous film in terms of structure. A barrier film is a dense oxide film with no pores, and the current flows through the insulating oxide film under a high electric field and grows thick. In the porous film, the first barrier film is made porous by locally forming pores under the action of a high electric field and the dissolving action of the electrolytic solution. Therefore, this type of film has a double structure of a barrier type part and a porous type part (FIG. 1).
1-2-2 Anodic oxidation of titanium In the growth process of a titanium anodic oxide film, it is considered that the movement of both titanium ions and oxygen contributes to the formation of the film. However, whether titanium ions move through the film and the film grows at the oxide / solution interface, whether the film grows at the metal / oxide interface due to oxygen movement, or proceeds simultaneously depending on the electrolysis conditions There is no established theory that can fully explain the mechanism.

Although the composition of the film varies depending on the type of electrolytic solution for titanium anodic oxidation and electrolysis conditions, titanium dioxide (TiO ₂ ) in which anatase type and rutile type are mixed is the main component. Further, in the film growth process, the amorphous film and the formation of anatase and rutile microcrystals occur in parallel, and therefore the film is composed of a mixture thereof.

  As an electrolytic solution, development using a molten salt, a non-aqueous solution, and an aqueous solution has been performed, but in recent actual production, an acid or alkaline aqueous solution is generally used.

  Electrolysis is usually performed by direct current electrolysis, but anodization can also be performed by alternating current electrolysis. Since the resistance of titanium anodized film increases as the film becomes thicker, the voltage is increased at a constant rate, or is switched to constant voltage electrolysis after reaching a predetermined voltage by a constant current density. In the anodic oxidation of titanium, the electrolytic behavior and the film formation rate differ depending on the type of electrolytic solution. As long as the same electrolytic bath is used, the thickness of the film is determined by the maximum voltage regardless of the current density, the pressure increase rate, the electrolysis time, and the like.

1-3 Lithium Ion Secondary Battery Utilizing Nanostructure When the size of a material is reduced to the nano order, physical properties different from those of bulk metals appear. The same applies to electrode materials for lithium ion secondary batteries. For example, lithium ion desorption / insertion into anatase TiO ₂ is possible, but even with rutile TiO ₂ , when the size is reduced to 15 nm, lithium ion desorption can be performed, and the discharge capacity reaches 365 mAhg ⁻ . In addition, the theoretical capacity of anatase type TiO ₂ is about 167 mAhg ^−, but the discharge capacity increases to 360 mAhg ⁻ with 6 nm nanoparticles. As described above, even in the case of the conventional active material, the discharge capacity is remarkably increased as the nano-size is reduced. This is an effect due to an increase in surface area. The performance improvement due to the increased surface area also appears in the output characteristics. This is because the lithium ions and the electrolyte solution can be easily transferred into the nanopores. As described above, since the nanoporous electrode has a large surface area, it is also interested in energy properties peculiar to nanomaterials such as lithium storage caused by surface chemical liquid reactivity. If the surface is used, there is a possibility that lithium exceeding the stoichiometric composition may be stored. By using the energy storage properties peculiar to nanocrystals, it is expected to realize an innovative lithium ion secondary battery electrode material having a large capacity and high output.

1-4 Purpose Currently, research is being conducted on the use of nanoporous TiO ₂ as an electrode in order to increase the capacity and power of lithium ion secondary batteries. As a conventional method for producing a nanoporous TiO ₂ electrode, anodic oxidation using an electrolytic solution containing fluoride ions is generally used. As described above, the surface area is increased by making the electrode have a nanoporous structure, and the lithium insertion / extraction characteristics are expected to be improved.

However, the nanoporous film formed only of TiO ₂ has a low conductivity, and in addition, fluoride ions contained in the electrolytic solution have a problem of adversely affecting the environment.
Therefore, in order to improve conductivity, nitrogen is introduced into the film from the electrolyte during anodic oxidation, and a composite film of TiO ₂ and TiN (conductivity TiO ₂ : 10 ⁻¹¹ to 10 ⁻¹² Ω−1 m ^−1). , TiN: 2.5 × 10 ⁶ Ω ⁻¹ m ⁻¹ ). In this research, aiming at the electrode material of the lithium ion secondary battery, the purpose is to create a TiO ₂ -TiN composite film by anodizing the Ti plate using an ammonium nitrate solution.

2-1 Test piece pure Ti plate (20 × 40 × 0.1 mm 99.5%) was used as a starting material.
2-2 Degreasing treatment The test piece shown in 2-1 was washed with distilled water after ultrasonic washing in acetone and ethanol for 10 minutes each. Thereafter, it was dried with Ar gas.

2-3 Anodic oxidation 2-3-1 Influence by voltage, current density, and temperature A schematic diagram of the experimental apparatus is shown in FIG. For the anodic oxidation, the test piece shown in 2-2 was used for the anode, graphite (30 × 100 × 8.0 mm) was used for the counter electrode, and 0.05M ammonium nitrate solution was used as the electrolyte. The solution was prepared by adding ion exchange water to 4.04 g of ammonium nitrate to 1.0 L. In order to efficiently remove the heat generated by the anodic oxidation, it was cooled in an ice bath, kept at a low temperature, and stirred. The anodic oxidation conditions are 15-25V for examining the influence of voltage, 3.0 × 10 ⁻³ −5.0 × 10 ⁻³ Acm ⁻² for examining the influence of current density, and for examining the influence of temperature. It was performed for 1 h at 1-10 ° C., respectively.
2-3-2 influence of electrolyte nitrate ion (NO 3 ^_-) corrosive is believed that it would be affecting the adhesion of the substrate and the oxide film, NO ₃ ^- by using the solution containing no Verification was performed. The solutions used for anodic oxidation and the anodic oxidation conditions are shown in Table 1.

2-3-3 Two-step anodic oxidation The first step is to form a dense film and cover the surface to improve adhesion, and the second step is to generate nitride in the oxide film. Staged anodic oxidation was performed. Anodization was performed using a sulfuric acid-based solution in the first stage and an ammonium nitrate solution in the second stage. 2 was used for anodic oxidation, 10 vol% sulfuric acid (100 V, 20 min, room temperature) or 2 M ammonium sulfate (100 V, 1 h, 5 ° C.) in the first stage, and 0.05 M ammonium nitrate (25 V in the second stage). , 1 h, 5 ° C.), and two-step anodic oxidation was performed. The adjustment of the solution is the same as the method shown in 2-3-1 or 2-3-2.

2-4 Characteristic Evaluation of Anodic Oxide Film A method for evaluating characteristics of the anodic oxide film obtained under each condition is shown below.
After the oxide film was vapor-deposited for 10 s with osmium, the oxide film surface / cross-sectional form was observed and the chemical composition was analyzed by EDS using FE-SEM (JEEL-JSM7001). Using XPS (PHI-5600) (CuKα ray), the chemical composition of the coating surface and inside was analyzed. Ar sputtering was performed for analysis of the inside of the film. The crystal structure was analyzed using XRD (RINT2000) (40 kV / 30 mA). After processing the oxide film with FIB, observation of the fine structure of the film and analysis of the crystal structure were performed by electron diffraction using TEM (JEOEL-JSM2100).
2-5 Characteristic Evaluation of Anodic Oxide Film as Lithium Ion Secondary Battery Electrode 2-5-1 Preparation of Electrode The two samples prepared in 2-3-3 were 10 × 40 × 0.1 mm (electrode area: 1. 0 × 1.0 cm) and heat-treated at 400 ° C. for 2 hours in an electric furnace was used as an electrode.

2-5-2 Production of Battery A pouch cell was produced in the manner shown in FIG. The procedure (1) was performed in air, and a working electrode was obtained by thermocompression bonding a sealant to the central portion of the sample shown in 2-5-1. The same operation was performed on the central part of the 3 cm nickel wire to obtain a lead wire connected to metallic lithium. In addition, the separator was formed into a bag size in which the working electrode was wrapped, and after placing each part as shown in the procedure (1), the A side and the B side were thermocompression bonded. The pouch and the lead wire produced in the procedure (1) were placed in an Ar-substituted glove box, and the procedure of the procedure (2) was performed. Metal lithium (Honjo Metal Co., Ltd.) was cut to 5.0 × 3.0 cm, and a nickel wire was sandwiched and folded in half and used as a counter electrode. The separator was sandwiched between the working electrode and the working electrode. Next, 1.0 mL of 1M LiPF ₆ / EC + EMC + DMC (1: 1: 1 vol.) Was poured into the cell as an electrolyte, and the C side was thermocompression bonded to form a bipolar pouch cell.

2-5-3 Constant Current Discharge Test Using the bipolar pouch cell prepared in 2-5-2, 50 cycles under the conditions of a current density of 50 mAcm ⁻² , a voltage range of 1.0 to 3.0 V, and a measurement temperature of 30 ° C. The constant current discharge test was conducted. For the measurement, HJ1010mSM8A charge / discharge device manufactured by Hokuto Denko was used.

2-6 Reagents The reagents used in the experiment are as follows.
Ammonium nitrate Wako Pure Chemical Industries, Ltd. Wako first grade ammonium sulfate Wako Pure Chemical Industries, Ltd. Special reagent grade sulfuric acid Wako Pure Chemical Industries, Ltd. Special reagent grade ammonia water Kanto Chemical Co., Ltd. Deer first grade

3-1 Anodic oxidation using ammonium nitrate solution 3-1-1 Influence of voltage The results of verifying the influence of voltage are shown below.
FIG. 4 shows a test piece after anodic oxidation at 0.05 ° C. for 1 h at 5 ° C. using a 0.05 M ammonium nitrate solution.
As can be confirmed from the SEM image of FIG. 5, a non-uniform film was formed at each voltage, and a more non-uniform film was formed as the voltage increased. Since a nanotube-like layer is formed inside the film (FIG. 5 (f)), it has been found that a nanoporous film may be formed by anodic oxidation using an ammonium nitrate solution.

FIG. 6 shows the result of XPS analysis of the chemical composition of the film shown in FIG. First, looking at the spectrum of the titanium region, the generation of TiO ₂ was confirmed because the peak of Ti ⁴⁺ appeared. Looking at the spectrum after sputtering, the Ti ³⁺ portion ^broadened , so it was confirmed that TiN was generated inside the coating. Furthermore, from the spectrum of the nitrogen region, the film surface is only adsorbed with nitrate ions (NO ₃ ⁻ ) and ammonium ions (NH ⁴⁺ ), but a nitride peak appears inside the film, suggesting the formation of TiN. These results suggest the formation of a composite film of TiO ₂ and TiN by anodizing with an ammonium nitrate solution.

3-1-2 Effect of Current Density / Temperature FIG. 7 and FIG. 8 show the results of verifying the influence of temperature when anodizing for 1 h at a constant current of 3.0 mAcm ⁻² . From the SEM image, it was confirmed that no porous material was formed at 1 ° C. and 5 ° C. One possible reason is that the voltage did not rise sufficiently. On the other hand, in the case of 10 ° C., the surface of the film was not uniform, but porous was partially formed.

Next, FIG. 9 shows the result of verifying the influence of temperature by increasing the current density to 5.0 mAcm ⁻² . In the case of 1 degreeC, it became a surface similar to the film | membrane formed in the case of 5 degreeC at 3.0 mAcm- ² . One reason for this is thought to be that the voltages that flowed during anodic oxidation were almost the same. When the temperature was 5 ° C., the film surface was uniform and the film having a porous structure was successfully formed. The film thickness is about 6.5 μm. However, it can be said that the cross section is lamellar and the film is very easy to peel off, so that the adhesion to the substrate is poor.

FIG. 10 shows the result of XPS analysis of the chemical composition of the sample subjected to anodization under conditions of current density of 5.0 mAcm ⁻² , 1 h, and 5 ° C. First, looking at the spectrum of the titanium region, the generation of TiO ₂ was confirmed because the peak of Ti ⁴⁺ appeared. Looking at the spectrum after sputtering, the portions of Ti ³⁺ and Ti ²⁺ were broad, and it was confirmed that TiN and TiO were generated inside the coating. Further, from the spectrum of the nitrogen region, it was found that the film surface was only adsorbed with NO ₃ ⁻ and NH ⁴⁺ , but nitride was formed inside the film.
The result of observing the above-mentioned sample with TEM is shown in FIG. FIG. 12 shows the EDS spectrum diagram. When the difference in crystal structure was confirmed by electron beam diffraction, the results were different, and it was found that the upper layer was an oxide film formed by anodic oxidation and the lower layer was a Ti plate.

3-2 Anodic oxidation using a solution not containing nitrate ions 3-2-1 System using sulfuric acid The results of verifying the influence of voltage using a 10 vol% sulfuric acid solution are shown in FIGS. FIG. 16 shows a test piece.
As can be seen from the SEM image, a non-uniform film is formed at 20-60V, a nanoporous film is not formed at 70-90V, and a nanoporous film with a pore diameter of 50-150 nm is formed at 100V and a uniform film is formed. Successful. One reason for this is thought to be a non-uniform surface because a sufficient current did not flow at a low voltage.

FIG. 17 shows the result of XPS analysis of the chemical composition of the film produced at 100V. Looking at the spectrum of the titanium region, a Ti ⁴⁺ peak appeared, confirming the formation of TiO ₂ . When the spectrum after sputtering was observed, it was found that a peak appeared in the Ti ²⁺ part, so that TiO was generated inside the film.

3-2-2 System Using Ammonium Sulfate FIG. 18 shows the results of verifying the influence of voltage using a 0.5 M ammonium sulfate solution. As a result of comparison at 15 to 25 V, a film with a non-uniform surface was formed in all cases. Since these films were similar to the films formed when the sulfuric acid solution was used, the results of verifying the influence of the concentration of the solution when the anodic oxidation was performed at 100 V are shown in FIG. As a result of comparison between the 0.5M and 2M solutions, nanoporouss with a pore diameter of 50 to 200 nm were formed at 2M, and a uniform film was successfully produced.

FIG. 20 shows the result of XPS analysis of the chemical composition of the film formed at 2M. First, looking at the spectrum of the titanium region, the generation of TiO ₂ was confirmed because the peak of Ti ⁴⁺ appeared. Looking at the spectrum after sputtering, the portions of Ti ³⁺ and Ti ²⁺ were broad, and it was confirmed that TiN and TiO ₂ were generated inside the coating. Further, from the spectrum of the nitrogen region, it was found that the surface of the film was only adsorbed with NH ⁴⁻ , but nitride was formed inside the film. From this result, it was found that a composite film of TiO ₂ and TiN was formed even when a solution not containing NO ₃ ^— was used. However, when comparing the peak intensities of the nitride, it was found that the ammonium nitrate solution was stronger, so that NO ₃ ⁻ was also involved in the formation of TiN.

The result of observing the above-mentioned sample with TEM is shown in FIG. An EDS spectrum is shown in FIG. When the difference in crystal structure was confirmed by electron diffraction, the results were different. Therefore, it can be said that the upper layer is an oxide film formed by anodic oxidation and the lower layer is a Ti plate.
3-2-3 System Using Ammonia Water FIG. 23 shows the results of verifying the influence of voltage using 10 vol% ammonia water. As a result of comparison at 15 to 25 V, a non-uniform film was formed and no porous film was formed.

The result of analyzing the chemical composition of the produced film by XPS is shown in FIG. First, looking at the spectrum of the titanium region, the generation of TiO ₂ was confirmed because the peak of Ti ⁴⁺ appeared. Further, from the spectrum of the nitrogen region, adsorption of NH ⁴⁺ and NO ₃ ⁻ was confirmed on the film surface.

3-3 Two-stage anodic oxidation 3-3-1 First stage: Sulfuric acid, Second stage: Ammonium nitrate The first stage is to form a dense film and improve the adhesion, and the second stage is oxidation. Two-step anodic oxidation was performed for the purpose of forming nitrides in the film.

First, 20V (FIG. 13), 50V (FIG. 14), and 100V (FIG. 15) are each used for 20 min at room temperature using a 10 vol% sulfuric acid solution in the first stage, and 0.05 h ammonium nitrate solution is used for 1 h at 5 ° C. in the second stage. FIG. 25 shows a current density-time curve when the anodic oxidation is performed. It can be seen that the porous layer is formed when the current density is stable in the barrier layer where the initial current density is unstable.
In addition, in FIG. 26, the external view of a test piece is shown. As can be seen from the SEM image of FIG. 27, the surfaces (a) and (c) where the surface was non-uniform at the first stage were further non-uniform after the second-stage anodic oxidation. On the other hand, the very uniform film formed in the first stage (e) was kept uniform even after the second stage anodization. Compared with the film formed by anodic oxidation using an ammonium nitrate solution, it was difficult for the film to peel off from the substrate, so it can be said that the adhesion between the substrate and the oxide film was improved.

  FIG. 28 shows the results of the observation of the cross-sectional form of the sample in which a uniform film was formed by two-step anodic oxidation and the analysis of the crystal structure by electron beam diffraction. From the SEM image, it was found that the film thickness was about 450 nm. Furthermore, it was found from the difference in crystal structure that a film having a two-layer structure of a p-formed layer formed in the first step of the upper layer and a layer formed in the second step of the lower layer was formed.

  29 and 30 are EDS spectrum diagrams.

The result of analyzing the chemical composition of the sample by XPS is shown in FIG. First, looking at the spectrum of the titanium region, the generation of TiO ₂ was confirmed because the peak of Ti ⁴⁺ appeared. Looking at the spectrum after sputtering, the portions of Ti ³⁺ and Ti ²⁺ were broad, and it was confirmed that TiN and TiO were generated inside the coating. Further, from the spectrum of the nitrogen region, it was found that the film surface was only adsorbed with NO ₃ ⁻ and NH ⁴⁺ , but nitride was formed inside the film.

3-3-2 First stage: ammonium sulfate, second stage: ammonium nitrate 100M, 5 ° C, 1h (FIG. 19) using 2M ammonium sulfate solution in the first stage, and 25V, 5 using 0.05M ammonium nitrate solution in the second stage The results of anodic oxidation at 1 ° C. for 1 h are shown in FIG. The surface of the film is uniform, and it can be said that the adhesion between the substrate and the oxide film was improved as before. From the SEM image of the cross section, it was found that a film having a two-layer structure having a film thickness of about 500 nm was formed.

3-4 Characteristic evaluation of anodized film as an electrode of a lithium ion secondary battery The sample prepared by two-step anodic oxidation was subjected to a heat treatment at 400 ° C. for 2 hours, and then the results of the characteristic evaluation as a battery are described below. Shown in
First, XRD patterns before and after the heat treatment of the used sample are shown in FIG. Compared with the XRD pattern of pure Ti, it can be seen that anatase-type TiO ₂ was produced by anodic oxidation. There was no significant peak change before and after the heat treatment.

FIG. 34 shows charge / discharge curves and cycle characteristics of a sample subjected to two-step anodic oxidation using a sulfuric acid solution in the first step and an ammonium nitrate solution in the second step. Maximum discharge capacity 17.3mAhcm ^-2 (3.8mAhnm ^-3), the discharge capacity 15.4mA ^hcm -2 (3.4mAhnm ^-3) capacity retention after next 50 cycles after 50 cycles a 89.2% It was. As a past study on the battery characteristics of a TiO ₂ film having a nanostructure, a discharge of 0.150 mAhcm ⁻² (15.0 mAhμm ⁻³ ) and a film of 9 μm (nanoporous) are discharged with a film having a thickness of 1 μm (nanotube) Results with a capacity of 0.240 mAhcm ⁻² (2.7 mAh μm ⁻³ ) have been reported. Compared with previous research results, the discharge capacity was improved despite the small film thickness, so the discharge capacity was improved. One reason for this is thought to be that the conductivity was improved by the inclusion of TiN in the film, and TiO ₂ was efficiently used.

Next, FIG. 34 shows charge / discharge curves and cycle characteristics of a sample subjected to two-stage anodic oxidation using an ammonium sulfate solution in the first stage and an ammonium nitrate solution in the second stage. The maximum discharge capacity was 60.0 mAhcm ⁻² (12.0 mAhnm ⁻³ ), the discharge capacity after 50 cycles was 51.7 mAhcm ⁻² (10.3 mAhnm ⁻³ ), and the capacity retention rate after 50 cycles was 86.6%. It was. Compared with the above sample, the discharge capacity was further improved. One reason for this is thought to be that the amount of TiN produced in the film increased due to the use of a solution containing NH ⁴⁺ in the first stage.
Incidentally, showing battery characteristics of the TiO ₂ film produced by anodic oxidation with sulfuric acid solution ((a) charge-discharge curve (b) cycle characteristics) in FIG. 36.
Anodic oxidation was performed under various conditions to try to create a nanoporous TiO ₂ —TiN composite film, and the characteristics of the lithium ion secondary battery were evaluated. The results obtained there are as follows.

(1) As a result of verifying the influence of voltage, current density, and temperature using an ammonium nitrate solution, the pore diameter was reduced by anodizing at 5-35 (preferably 20-25 V) or 3.0-5.0 mAcm ^−2. A nanoporous film having a diameter of 25 nm and a distance between pores of about 80 nm was formed.
(2) From the XPS analysis results, it was confirmed that TiN was produced in addition to TiO ₂ in the film produced by anodic oxidation using an ammonium nitrate solution, so that a TiO ₂ —TiN composite film was produced.
(3) As a result of anodic oxidation using a sulfuric acid solution or an ammonium sulfate solution, a nanoporous film having a pore diameter of 50 to 150 nm, a distance between pores of about 250 nm, and a film thickness of 450 to 500 nm was formed at 100 V.
(4) As a result of two-step anodic oxidation using a sulfuric acid solution or an ammonium sulfate solution in the first stage and an ammonium nitrate solution in the second stage, a nanoporous TiO ₂ —TiN composite film having good adhesion was formed.
(5) As a result of evaluating the characteristics of the battery using a sample prepared by two-step anodic oxidation, the result is that the maximum discharge capacity is 60.0 mAhcm ⁻² (12.0 mAhnm ⁻³ ) and the capacity maintenance ratio is 86.6%. Obtained.

From the above, application of the nanoporous TiO ₂ —TiN composite film as a binder-free lithium ion secondary battery electrode can be expected.

Claims (20)

A method for producing a porous anodic oxide film, comprising using a nitric acid-based electrolyte and anodizing a Ti substrate under a voltage of less than 100V. The method for producing a porous anodic oxide film according to claim 1, wherein the pH of the electrolytic solution is 11 or less. The method for producing a porous anodized film according to claim 1 or 2, wherein the voltage is 5-35V. The method for producing a porous anodized film according to any one of claims 1 to 3, wherein a current density during the anodization is 3.0 to 5.0 mAcm ^-2 . The method for producing a porous anodic oxide film according to any one of claims 1 to 4, wherein the nitric acid-based electrolytic solution is an ammonium nitrate solution. A method for producing a porous anodic oxide film, characterized by anodizing a Ti substrate under a voltage of 70 V or more using a sulfuric acid electrolyte. The method for producing a porous anodic oxide film according to claim 6, wherein the voltage is 100 V or more. The method for producing a porous anodic oxide film according to claim 6 or 7, wherein the pH of the electrolytic solution is 11 or less. 9. The method for producing a porous anodic oxide film according to claim 6, wherein the sulfuric acid electrolyte is a sulfuric acid solution or an ammonium sulfate solution. A method for producing a multilayer porous anodized film, comprising performing a second anodizing step with a nitric acid solution or an ammonium nitrate solution after a first anodizing step with a sulfuric acid solution or an ammonium sulfate solution. The method for producing a multilayer porous anodized film according to claim 10, wherein a sulfuric acid solution is used in the first anodizing step, and ammonium nitrate is used in the second anodizing step. The method for producing a multilayer porous anodized film according to claim 10, wherein an ammonium sulfate solution is used in the first anodizing step, and ammonium nitrate is used in the second anodizing step. A porous anodized film formed on a Ti substrate with an average pore diameter of about 10-30 nm and a distance between pores of 80 nm or more. The anodized film according to claim 13, wherein the anodized film is a composite oxide film of TiO ₂ —TiN. A porous anodized film formed on a Ti substrate with an average pore diameter of 50 to 150 nm and a distance between pores of 250 nm or more. A film having an average pore diameter of about 10-30 nm and a distance between pores of 80 nm or more and a film having an average pore diameter of 50-150 nm and a distance between pores of 250 nm or more are formed on a Ti substrate. Porous anodized film. The porous anodic oxide film according to any one of claims 13 to 16, wherein the film is crystalline. An electrode comprising the porous anodized film according to any one of claims 13 to 17. The electrode according to claim 18, wherein the electrode is an electrode for a lithium ion secondary battery. A battery comprising the electrode according to claim 18 or 19.

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