JP5038588B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to a method for producing titania having an anatase type crystal structure used as a negative electrode material of a lithium secondary battery and a lithium secondary battery having a negative electrode mainly composed of the titania.

  Secondary batteries using carbon as the negative electrode instead of lithium metal have been put into practical use. A lithium metal negative electrode generates dendrite with charge and discharge, which causes deterioration of characteristics and internal short circuit. However, in a battery using carbon for the negative electrode, this dendrite is difficult to generate. However, carbon has a high reactivity with an electrolytic solution in a state where lithium is occluded, and has a problem that a lithium-containing film is formed on the surface and the amount of movable lithium is reduced.

  Therefore, conventionally, in order to replenish lithium consumed in the formation of the lithium-containing film, metallic lithium is directly attached to the negative electrode active material, and the negative electrode active material is placed in the electrolytic solution. Depending on the concentration difference, a method of occluding lithium ions in the negative electrode active material, a method of thinly depositing a metal that does not form an alloy with lithium on carbon to suppress a reaction with the electrolytic solution, etc. have been proposed (for example, , See Patent Document 1). In order to avoid the disadvantages of using carbon, it is also proposed to use transition metal oxides such as tungsten oxide, molybdenum oxide, and titania, or to use them in combination (for example, see Non-Patent Document 1). .) Above all, anatase-type titania has been attracting attention as a lithium ion host material because of its large capacity, low cost, and harmlessness. Nanoparticle titania and nanotube-shaped titania produced by hydrothermal synthesis method are used as electrodes. It has been reported that a relatively large capacity is used (see, for example, Non-Patent Documents 2 to 5).

  Since the capacity, efficiency, reversibility, and stability of lithium ion insertion into titania depend greatly on the form of the electrode, the application of a material with a unique shape such as a nanotube is highly expected, and its manufacturing method Many studies have been made on. However, the hydrothermal synthesis method has a problem that it is difficult to accurately control the structure, such as obtaining titania having various shapes such as nanofibers, nanorods, nanotubes, and nanoribbons depending on experimental conditions. In addition, attempts have been made to control the shape by coexisting a mold, but improvement of productivity in addition to the structure is also an issue.

Japanese Patent Laid-Open No. 11-185809 Jay Jay Orbon et al., “Journal of Electrochemical Society”, 1987, vol. 134, p. 638-641 See Natarajan et al., “Electrochimica Acta”, 1998, Vol. 43, p. 3371-3374 S Y Fan et al., “Journal of Electrochemical Society”, 1995, vol. 142, p. L142-L144 Y. K. Zou et al., “Journal of Electrochemical Society”, 2003, vol. 150, p. A1246-A1249 El Cavan et al., “Chemistry of Materials”, 2004, Vol. 16, p. 477-485

  The present invention has been made in view of such a situation, and a method for producing a negative electrode material for a lithium secondary battery containing anatase-type titania nanotubes excellent in industrial productivity, and a lithium secondary battery using the same Is to provide.

  That is, the present invention relates to a method for producing anatase titania for use in a lithium secondary battery, characterized in that titanium or a titanium-containing alloy is electrolytically oxidized to form nanotube-shaped titania having an aspect ratio of 6 or more.

  The present invention also relates to a lithium secondary battery containing anatase-type titania, wherein the titania is obtained by electrolytic oxidation of titanium or an alloy containing titanium, and has a nanotube-shaped titania having an aspect ratio of 6 or more. The present invention relates to a lithium secondary battery.

  In addition, the present invention has a negative electrode in which titanium or a titanium-containing alloy is obtained by electrolytic oxidation of a powdery titania nanotube and a negative electrode layer mainly composed of a binder on one or both sides of the current collector. It is related with the said lithium secondary battery characterized.

  The present invention also relates to the lithium secondary battery having a negative electrode mainly composed of a titanium-titania composite electrode obtained by electrolytic oxidation of titanium or an alloy containing titanium.

Hereinafter, the present invention will be described in detail.
The lithium secondary battery of the present invention is composed of a positive electrode, a negative electrode, a separator, a nonaqueous electrolyte (for example, a lithium salt-containing electrolyte) and the like, and anatase titania having a nanotube shape used for the negative electrode is a method described below. It can be obtained by electrolytic oxidation of titanium metal or an alloy containing titanium as a main component (hereinafter also referred to as titanium alloy).
In the electrolytic oxidation according to the present invention, titanium or a titanium alloy is used as an anode in an electrolyte, and an arbitrary conductive material is used as a cathode, whereby an oxide is formed on the anode surface by applying a voltage. In the present invention, the state in which titanium or a titanium alloy is an anode may be only once during anodizing treatment, and includes the case where the anode and the cathode are alternately performed.

In the case of using a titanium alloy, elements other than titanium contained in the alloy are elements that are mostly eluted under electrolytic oxidation conditions. The proportion of titanium in the alloy in the entire alloy is preferably 30% by weight or more, and more preferably 50% by weight or more.
Examples of titanium or titanium alloy that can be used in the present invention include industrial pure titanium prepared from oxygen, iron, nitrogen, and hydrogen, and low alloy titanium alloys having a certain degree of press formability. Specifically, JIS Class 1, 2, 3, and 4 industrial pure titanium, alloys with improved corrosion resistance by adding nickel, ruthenium, tantalum, palladium, etc., aluminum, vanadium, molybdenum, tin, An alloy added with iron, chromium, niobium, or the like can be given.

  As for the shape, in addition to various shapes such as titanium or titanium alloy plates, rods, meshes, etc., plates or rods, meshes, etc. grown on titanium or titanium alloys as a film, plates Examples thereof include, but are not limited to, those obtained by growing titanium or a titanium alloy as a film on the surface of a semiconductor or insulating material such as a rod or mesh. Regarding surface smoothness, titania can be grown in the electrolytic oxidation process even if the surface structure has a complicated shape, and the smoothness is not limited.

In order to produce nanotube-shaped titania, the type of electrolyte solution used for electrolytic oxidation is important. In the present invention, it is essential that the electrolyte solution used for electrolytic oxidation contains ions containing halogen atoms. The ion containing a halogen atom here is an ion containing any atom of fluorine, chlorine, bromine and iodine, specifically, fluoride ion, chloride ion, bromide ion, iodide ion, Examples include perchlorate ion, chlorate ion, bromate ion, iodate ion, chlorite ion, bromite ion, hypochlorite ion, hypobromite ion, hypoiodite ion and the like. These ions may be used alone or as a mixture of two or more.
As the electrolyte solution containing these ions, either aqueous or non-aqueous can be used, but aqueous is preferred. Specifically, an aqueous solution of an acid or salt that forms ions containing a halogen atom is used.
The concentration is preferably 0.0001 to 10% by volume as an acid or salt, and a relatively high concentration, specifically 0.1 to 10% by volume, more preferably 0 in order to obtain nanotubes in powder form. In the range of 2 to 5% by volume, in order to obtain a titanium-titania composite electrode, a relatively low concentration, specifically 0.0001 to 0.1% by volume, more preferably 0.002 to 0.02 is obtained. It is in the range of volume%.
In the present invention, a perchloric acid aqueous solution is particularly suitable as the electrolyte solution.

The electrolyte solution may contain an acidic compound different from the acid or salt that forms ions containing halogen atoms. By containing an acidic compound, the reaction rate such as promoting or suppressing the anodic oxidation rate can be controlled.
Examples of such acidic compounds include sulfuric acid, nitric acid, acetic acid, hydrogen peroxide, oxalic acid, phosphoric acid, chromic acid, glycerophosphoric acid and the like in addition to the above-mentioned halide or acid of its oxidant ion. Is not to be done. The concentration is preferably in the range of 0.001 to 1000, more preferably 0.01 to 50, and still more preferably 0.04 to 5 in terms of molar ratio to the halogen atom-containing ions.

In the electrolytic oxidation, the applied voltage is usually 5 to 200 V, preferably 10 to 150 V, more preferably 14 V to 110 V. The current density is preferably 0.2 to 500 mA / cm ² , more preferably 0.5 to 100 mA / cm ² . The treatment time is preferably 1 minute to 24 hours, more preferably 5 minutes to 10 hours. Moreover, 0-50 degreeC is preferable and the temperature of the electrolyte aqueous solution at the time of anodization has more preferable 0-40 degreeC.

By the above method, a nanotube-shaped titania having an aspect ratio of 6 or more can be obtained. The aspect ratio is the ratio of the length to the diameter. By using the method of the present invention, a nanotube-shaped titania having an aspect ratio of 6 or more, preferably 10 or more, more preferably 20 or more, and further preferably 30 or more is obtained. Can do.
The diameter of the nanotube-shaped titania of the present invention varies depending on the production conditions and the like, but is usually 5 nm to 500 nm, preferably 5 nm to 100 nm. The length also varies depending on the production conditions and the like, but is usually 0.1 μm to 100 μm, preferably 1 μm to 50 μm.

  The obtained nanotube-shaped titania can grow an anatase type crystal structure by performing post-treatment such as heat treatment, water vapor treatment, and ultraviolet irradiation. For example, in the case of heat treatment, an anatase type crystal structure grows by performing treatment at a temperature of 100 ° C. to 650 ° C. for 10 minutes to 500 minutes, preferably at a temperature of 300 ° C. to 600 ° C. for 30 minutes to 160 minutes. I can expect that. Note that the structure does not collapse by these treatments.

  Next, the positive electrode, negative electrode, separator, and non-aqueous electrolyte of the lithium secondary battery of the present invention will be described.

  In the positive electrode, a mixture of a positive electrode active material, a conductive agent, and a binder is supported on one side or both sides of a positive electrode current collector.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and lithium. Examples thereof include vanadium oxide and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, lithium-containing cobalt oxide (for example, LiCoO ₂ ), lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2 O ₂ ), lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂₎ ) Is preferable because a high voltage can be obtained. As the positive electrode active material, an oxide may be used alone, or two or more kinds of oxides may be mixed and used.

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  The binder has a function of holding the active material on the current collector and connecting the active materials to each other. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyether sulfone, ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). be able to.

  About each compounding ratio of a positive electrode active material, a electrically conductive agent, and a binder, a positive electrode active material is 65 to 98 weight%, Preferably it is 80 to 95 weight%, A conductive agent is 1 to 30 weight%, Preferably it is 3 to 3 weight%. It is 20% by weight, and the binder is in the range of 1 to 10% by weight, preferably 2 to 7% by weight.

As the positive electrode current collector, a conductive substrate having a porous structure or a nonporous conductive substrate can be used. These conductive substrates can be formed from aluminum, stainless steel, or nickel, but are not limited thereto.
The thickness of the positive electrode current collector is preferably 2 to 30 μm, more preferably 5 to 20 μm. By making the thickness of the positive electrode current collector in the range of 2 to 30 μm, the balance between electrode strength and weight reduction becomes good, and in particular, the balance becomes better at 5 to 20 μm.

  The positive electrode can be produced by suspending a positive electrode active material, a conductive agent and a binder in a solvent, and applying the suspension to a current collector and drying to form a thin plate. Examples of the solvent to be used include toluene, N-methyl-2-pyrrolidone and the like, but are not limited thereto.

  In the negative electrode, a mixture of a negative electrode active material, a conductive agent, and a binder is supported on one side or both sides of a negative electrode current collector.

  As the negative electrode active material, powdered titania nanotubes obtained by electrolytic oxidation of titanium or an alloy containing titanium are used. In addition to this titania nanotube, titania particles, carbonaceous materials that occlude and release lithium ions, metals that occlude and release lithium ions, metal oxides that occlude and release lithium ions, metal sulfides that occlude and release lithium ions, lithium A metal nitride that occludes and releases ions, lithium metal that occludes and releases lithium ions, or a lithium alloy that occludes and releases lithium ions can also be mixed and used.

Carbonaceous materials include graphite, coke, carbon fiber, spherical carbon and other graphite or carbonaceous materials, or thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, or mesophase microspheres. It is preferable to use a graphite material or a carbonaceous material obtained by performing heat treatment at 500 to 3000 ° C.
Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.
Examples of the metal sulfide include tin sulfide and titanium sulfide.
Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.
Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.

  As the conductive agent, for example, acetylene black, carbon black, graphite or the like is preferably used.

  As the binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-diene copolymer, styrene-butadiene rubber, carboxymethylcellulose and the like can be used.

  About each compounding ratio of a negative electrode active material, a electrically conductive agent, and a binder, a negative electrode active material is 65 to 98 weight%, Preferably it is 80 to 95 weight%, A conductive agent is 1 to 30 weight%, Preferably it is 5 to 5 weight%. 25% by weight and the binder is in the range of 1-7% by weight, preferably 2-5% by weight.

As the negative electrode current collector, a conductive substrate having a porous structure or a nonporous conductive substrate can be used. These conductive substrates can be formed from copper, stainless steel, or nickel, but are not limited thereto.
The thickness of the negative electrode current collector is preferably 2 to 30 μm, more preferably 5 to 20 μm. By making the thickness of the negative electrode current collector in the range of 2 to 30 μm, the balance between electrode strength and weight reduction becomes good, and in particular, the balance becomes better at 5 to 20 μm.

For example, the negative electrode is obtained by suspending a negative electrode active material, a conductive agent, and a binder in a solvent, applying the suspension to a current collector, drying, and then pressing 1-5 times at a desired pressure. Can be produced. Examples of the solvent to be used include toluene, N-methyl-2-pyrrolidone and the like, but are not limited thereto. The negative electrode preferably has a packing density d after pressing of 1.4 g / cm ³ or more and 1.6 g / cm ³ or less.

  When a titanium-titania composite electrode obtained by electrolytic oxidation of titanium or an alloy containing titanium is used as the negative electrode, the current collector is titanium or an alloy containing titanium.

As the negative electrode layer (active part of the negative electrode), a layer made of only titania formed by electrolytic oxidation can be used, or in addition to the titania layer on its surface, the above-mentioned carbonaceous materials and lithium ions are occluded and released. Metals, metal oxides that occlude and release lithium ions, metal sulfides that occlude and release lithium ions, metal nitrides that occlude and release lithium ions, lithium metal that occludes and releases lithium ions or lithium alloys that occlude and release lithium ions It is also possible to form layers.
Methods for forming these layers include vapor deposition methods such as vacuum deposition, chemical vapor deposition, and sputtering, liquid phase methods such as spin coating, dip coating, and liquid phase growth, spraying, and solid phase. Examples include a solid phase method such as a method using a reaction, a heat treatment method, and a method of coating fine particle colloid.

  When the titania layer is provided, the particle size of the titania particles is generally on the order of nm to μm, but the particle size of the primary particles obtained from the diameter when the projected area is converted into a circle is preferably 5 to 200 nm, more preferably 8-100 nm. In the case of the method of applying titania fine particle colloid, the average particle size of the secondary particles in the dispersion is preferably 0.01 to 10 μm, more preferably 0.05 to 1 μm.

  After the titania fine particles are coated on the titanium-titania composite electrode, heat treatment is performed to improve the electrical contact between the titania fine particles and to improve the coating strength and the adhesion with the titanium-titania composite electrode. preferable. In the heat treatment, the treatment is performed at a temperature of 100 ° C. to 650 ° C. for 10 minutes to 500 minutes, preferably at a temperature of 300 ° C. to 600 ° C. for 30 minutes to 160 minutes.

  After the heat treatment, the crystal solution using a chemical plating treatment using a titanium tetrachloride aqueous solution, an electrochemical plating treatment using a titanium trichloride aqueous solution, or an aqueous solution containing titanium fluoride, ammonium hexafluorotitanate, or titanyl sulfate. By performing the phase growth, the adhesion between the titania fine particles and between the titanium-titania composite electrode and the titania fine particles can be further improved.

  As the separator, a microporous resin film, a woven fabric, a non-woven fabric, a laminate of the same material or different materials among these can be used. In particular, a microporous resin film causes a so-called shutdown phenomenon in which when the temperature of the electrode group is abnormally increased due to heat generation due to overcharge or the like, the resin constituting the separator is plastically deformed and closes the fine pores, so that the lithium ion This is preferable because the flow is cut off, further heat generation is prevented, and the overcharge state can be safely terminated. Examples of the material for forming the separator include polyethylene, polypropylene, ethylene-propylene copolymer, and ethylene-butene copolymer. As a material for forming the separator, one type or two or more types selected from the types described above can be used.

The non-aqueous electrolyte is preferably a lithium salt-containing electrolyte composed of a solvent and a lithium salt.
Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyllactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, and 1,3. -Dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl oxalate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazodinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl Examples of the solvent include at least one of aprotic organic solvents such as ether and 1,3-propane sultone, or a mixture of two or more. It is.
The lithium salt, lithium salt dissolved in the solvent is used, _{specifically, LiClO 4, LiBF 4, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10 , LiAlCl ₄ , lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate and the like. These can also be used as a mixture of two or more.
In addition to the non-aqueous electrolyte, an organic solid electrolyte can also be used. Examples thereof include a polyethylene derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, and a phosphate ester polymer.

  The use of the lithium secondary battery of the present invention is not particularly limited. For example, electronic devices such as notebook computers, laptop computers, pocket word processors, mobile phones, cordless phones, portable CDs, radios, automobiles, electric vehicles, and game devices. Consumer electronics such as Further, the shape of the secondary battery can be applied to any of coins, buttons, sheets, cylinders, corners, and the like.

  By the method of the present invention, it is possible to industrially advantageously produce anatase-type crystal titania having a nanotube shape having a sufficient aspect ratio as a main component of the negative electrode active material of a lithium secondary battery.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
<Production of electrode>
The electrode according to the present invention was manufactured by the following procedure.
First, a titanium plate (purity: 99.7% by weight) having a size of 10 cm × 4 cm and a thickness of 0.5 mm was prepared and subjected to ultrasonic cleaning in ethanol for 5 minutes. Next, titania in powder form was obtained by subjecting titanium to constant voltage electrolytic oxidation at 30 V for 5 hours in an aqueous electrolyte solution composed of an aqueous perchloric acid solution having a concentration of 0.1% by volume and a temperature of 16 ° C.
When the obtained powder was observed with a transmission electron microscope, as shown in FIG. 1, it had a nanotube structure with a diameter of about 40 nm, a length of 10 μm (aspect ratio 250), and fired at 450 ° C. for 1 hour. Thus, an anatase type crystal structure was shown as shown in FIG.
The fired titania nanotube powder, acetylene black and polyvinylidene fluoride (trade name “KF polymer” manufactured by Kureha Chemical Industry Co., Ltd.) are mixed at a weight ratio of 80: 15: 5, and N-methyl-2- Pyrrolidone was added and these were kneaded to prepare a paste. This paste was applied to one side of a 10 μm thick Cu foil, dried and pressed to produce an electrode. The thickness of the active part (negative electrode layer) of the obtained electrode was 80 μm, and its weight was 20.2 mg / cm ² .

《Electrochemical measurement》
The produced electrode was dried at 150 ° C. in a vacuum dryer.
Cyclic voltammogram measurement was performed under an argon atmosphere at room temperature at the working electrode, lithium metal as the counter electrode and the reference electrode, LiPF ₆ 1 mol / L ethylene carbonate-dimethyl carbonate mixed solution (volume ratio 1: 1) as the electrolyte. ) Was performed in a range from 2.5 V to 1.0 V at a running speed of 0.05 mV / s with respect to the reference electrode.
Charging / discharging was performed at a constant current of 80 mA / g, cathodic polarization was up to 1.0 V, and anodic polarization was up to 2.5 V, and the amount of electricity and elapsed time at that time were calculated.

Fig. 3 shows the cyclic voltammogram of the fabricated electrode. On the cathode side corresponding to lithium insertion, two large peaks are observed near 1.7V and two small peaks near 1.5V. On the corresponding anode side, two large peaks were observed near 2.1V and two small peaks near 1.6V.
The capacity of this electrode after 3 cycles showed a large value of 172 mAh / g, and after 10 cycles showed 168 mAh / g, almost unchanged characteristics.

[Example 2]
<Production of electrode>
The electrode according to the present invention was manufactured by the following procedure.
First, a titanium plate (purity: 99.7% by weight) having a size of 10 cm × 4 cm and a thickness of 0.5 mm was prepared and subjected to ultrasonic cleaning in ethanol for 5 minutes. Next, titania in powder form was obtained by subjecting titanium to constant-voltage electrolytic oxidation at 30 V for 3 hours in an aqueous electrolyte solution composed of a perchloric acid aqueous solution having a concentration of 0.5 vol% and a temperature of 16 ° C.
The obtained powder had a nanotube structure with a diameter of about 40 nm as in FIG. 1 and a length of 10 μm. However, when the powder was fired at 450 ° C. for 1 hour, as shown in FIG. A crystal structure with mixed type and brookite type was shown.
The fired titania nanotube powder, acetylene black and polyvinylidene fluoride (trade name “KF polymer” manufactured by Kureha Chemical Industry Co., Ltd.) are mixed at a weight ratio of 80: 15: 5, and N-methyl-2- Pyrrolidone was added and these were kneaded to prepare a paste. This paste was applied to one side of a 10 μm thick Cu foil, dried and pressed to produce an electrode. The thickness of the active part (negative electrode layer) of the obtained electrode was 80 μm, and its weight was 20.1 mg / cm ² .

《Electrochemical measurement》
Using the produced electrode, electrochemical measurement was performed in the same manner as in Example 1. In the cyclic voltammogram measurement, a large peak near 1.7 V on the cathode side and a large peak near 2.1 V on the anode side were the same as in Example 1, but two peaks near 1.5 V on the cathode side were found. A peak and two peaks near 1.6 V on the anode side were observed to be relatively large as compared with Example 1.
The capacity of this electrode after 3 cycles showed a large value of 150 mAh / g, and after 10 cycles it showed 153 mAh / g, almost unchanged characteristics.

[Comparative Example 1]
<Production of electrode>
Nano-sized titania paste (Ti-Nanoxide T manufactured by SOLARONIX) was dried, fired at 450 ° C. for 1 hour, and pulverized to obtain anatase-type titania powder. The obtained powder, acetylene black and polyvinylidene fluoride (trade name “KF polymer”: manufactured by Kureha Chemical Industry Co., Ltd.) were mixed at a weight ratio of 80: 15: 5, and N-methyl-2-pyrrolidone was mixed. In addition, these were kneaded to prepare a paste. This paste was applied to one side of a 10 μm thick Cu foil, dried and pressed to produce an electrode. The thickness of the active part (negative electrode layer) of the obtained electrode was 75 μm, and its weight was 18.8 mg / cm ² .
《Electrochemical measurement》
When the electrochemical measurement was performed by the method similar to Example 1 using the produced electrode, the capacity | capacitance after 3 cycles was 43 mAh / g and 10 mA after that was 38 mAh / g.

[Comparative Example 2]
<Production of electrode>
According to JP-A-2002-241129, titania nanotubes were dissolved in an aqueous ethanol solution by dissolving titanium isopropoxide, and diluted hydrochloric acid was added as a hydrolysis catalyst and allowed to stand, followed by firing at 600 ° C. for 2 hours. The pulverized titania powder was dispersed in a 20 wt% aqueous sodium hydroxide solution, hydrothermally synthesized at 110 ° C. for 20 hours, and neutralized and washed with hydrochloric acid to obtain titania nanotubes. The obtained tube had a diameter of 8 nm and an average length of 150 nm. However, it took a lot of time and many amorphous crystals were also seen.
This sample was calcined at 450 ° C. for 1 hour and pulverized to obtain anatase-type titania powder. The obtained powder, acetylene black and polyvinylidene fluoride (trade name “KF polymer”: manufactured by Kureha Chemical Industry Co., Ltd.) were mixed at a weight ratio of 80: 15: 5, and N-methyl-2-pyrrolidone was mixed. In addition, these were kneaded to prepare a paste. This paste was applied to one side of a 10 μm thick Cu foil, dried and pressed to produce an electrode. The thickness of the active part (negative electrode layer) of the obtained electrode was 75 μm, and its weight was 19.6 mg / cm ² .
《Electrochemical measurement》
When the electrochemical measurement was performed by the method similar to Example 1 using the produced electrode, the capacity | capacitance after 3 cycles was 144 mAh / g after 10 cycles, and was 143 mAh / g.

Table 1 shows the performance of various electrodes using powdered titania.
From the results shown in Table 1, the electrode produced using the titania powder mainly composed of nanotube-shaped anatase structure according to the present invention is an electrode produced using conventional titania particle powder or nanotube titania powder produced by hydrothermal synthesis. It can be seen that the capacity per weight is relatively large.

[Example 3]
<Production of electrode>
The electrode according to the present invention was manufactured by the following procedure.
First, a titanium foil having a size of 6 cm × 1.5 cm and a thickness of 0.05 mm (purity: 99.7% by weight) was prepared, and subjected to ultrasonic cleaning in ethanol for 5 minutes. Next, a titanium-titania composite electrode was obtained by subjecting titanium to a constant current electrolytic oxidation at 50 mA / cm ² for 1.5 hours in an aqueous electrolyte solution composed of an aqueous perchloric acid solution having a concentration of 0.006% by volume and a temperature of 16 ° C. Obtained. The obtained composite electrode was baked at 450 ° C. for 1 hour and observed with a scanning electron microscope to obtain anatase titania having a tube structure as shown in FIG. The diameter of the tube was 40 nm and the length was 15 μm (aspect ratio 375). The titania on the composite electrode was 4.5 mg / cm ^{2 on} both sides.

《Electrochemical measurement》
Using the produced electrode, electrochemical measurement was performed in the same manner as in Example 1. In the cyclic voltammogram measurement, the same peak as in Example 1 was observed.
The capacity of this electrode after 3 cycles was as large as 212 mAh / g, and after 10 cycles it was 220 mAh / g, showing almost unchanged characteristics.

[Example 4]
<Production of electrode>
The electrode according to the present invention was manufactured by the following procedure.
First, a titanium foil having a size of 6 cm × 1.5 cm and a thickness of 0.05 mm (purity: 99.7% by weight) was prepared, and subjected to ultrasonic cleaning in ethanol for 5 minutes. Next, a titanium-titania composite electrode was obtained by subjecting titanium to a constant current electrolytic oxidation at 50 mA / cm ² for 1.5 hours in an aqueous electrolyte solution composed of an aqueous perchloric acid solution having a concentration of 0.006% by volume and a temperature of 16 ° C. Obtained. On the obtained composite electrode, nano-sized titania paste (Ti-Nanoxide T manufactured by SOLARONIX) was applied on both sides with a gap of about 120 μm using an applicator and dried at 80 ° C. The composite electrode was fired at 450 ° C. for 1 hour. The titania on the composite electrode was 6.4 mg / cm ^{2 on} both sides.

《Electrochemical measurement》
Using the produced electrode, electrochemical measurement was performed in the same manner as in Example 1. In the cyclic voltammogram measurement, the same peak as in Example 1 was observed.
The capacity of this electrode after 3 cycles was as large as 192 mAh / g, and after Cycle 10 it was 191 mAh / g.

[Comparative Example 3]
<Production of electrode>
A 0.05 mm thick titanium foil (purity 99.7% by weight) was prepared and subjected to ultrasonic cleaning in ethanol for 5 minutes. On both sides, nano-sized titania paste (Ti-Nanoxide T manufactured by SOLARONIX) was applied to both sides with a gap of about 120 μm using an applicator, dried at 80 ° C., and baked at 450 ° C. for 1 hour. The titania on the titanium foil was 1.6 mg / cm ^{2 on} both sides.
《Electrochemical measurement》
When the electrochemical measurement was performed by the method similar to Example 1 using the produced electrode, the capacity | capacitance after 3 cycles was 54 mAh / g, and after 10 cycles, it was 55 mAh / g.

Table 2 shows the performance of the titanium-titania composite electrode.
From the results of Table 2, it can be seen that the titanium-titania composite electrode according to the present invention has a larger capacity per weight than the conventional one.

2 is a transmission electron microscope photograph of titania prepared in Example 1. FIG. 2 is an X-ray structural diffraction pattern of titania prepared in Example 1. FIG. 2 is a cyclic voltammogram of an electrode using titania produced in Example 1. FIG. 3 is an X-ray structural diffraction pattern of titania prepared in Example 2. FIG. 4 is a photograph of a scanning electron microscope of titania prepared in Example 3.

Claims (4)

  A method for producing anatase-type titania used as a negative electrode active material of a lithium secondary battery, characterized in that nanotube-shaped titania having an aspect ratio of 6 or more is formed by electrolytic oxidation of titanium or an alloy containing titanium.   A lithium secondary battery containing anatase-type titania as a negative electrode active material, wherein the titania is obtained by electrolytic oxidation of titanium or an alloy containing titanium, having an aspect ratio of 6 or more and a length of 1 to 50 μm A lithium secondary battery comprising a nanotube-shaped titania. A negative electrode layer mainly composed of a binder and a negative electrode active material composed of nanotube-shaped anatase titania having an aspect ratio of 6 or more and a length of 1 to 50 μm obtained by electrolytic oxidation of titanium or an alloy containing titanium. 3. The lithium secondary battery according to claim 2, further comprising a negative electrode supported on one side or both sides of the current collector. Titanium or an alloy containing titanium has a negative electrode mainly composed of a titanium-titania composite electrode in which nanotube-shaped anatase-type titania having an aspect ratio of 6 or more and a length of 1 to 50 μm is formed on the surface by electrolytic oxidation. The lithium secondary battery according to claim 2.