JP6120263B2 - Manufacturing method of fiber cathode for lithium secondary battery using electrolytic deposition method - Google Patents

Description

The present invention relates to a method for producing a fiber cathode for a lithium secondary battery in which a cathode active material containing a Li-Mn composite oxide is formed on a carbon fiber surface .

  In recent years, with the spread of portable electronic devices such as notebook computers, mobile phones or personal digital assistants (PDAs), these devices are used as a power source in order to reduce their weight and enable long-term use. There is a demand for miniaturization and high energy density of secondary batteries. Conventionally, nickel-cadmium batteries, nickel-hydrogen batteries, and the like have been mainstream as secondary batteries, but use of lithium secondary batteries tends to increase due to demands for miniaturization and high energy density.

  Current lithium secondary batteries generally use a non-aqueous electrolyte solution in which lithium ions are dissolved in an organic solvent such as lithium cobaltate as a positive electrode active material, a carbon electrode as a negative electrode, and propylene carbonate as an electrolyte.

As a general manufacturing method of lithium cobaltate (LiCoO ₂ ), which is a positive electrode active material for lithium secondary batteries, lithium carbonate (Li ₂ CO ₃ ) and cobalt hydroxide (Co (OH) ₂ ) are used as starting materials. A method of firing at a high temperature using a bismuth is widely known. However, in this manufacturing method, it is necessary to heat the material at a high temperature of 700 to 900 ° C., and the manufacturing cost is high. Cobalt reserves are estimated to be as low as 8.4 million tons, and the price of cobalt may rise in the future, and alternative materials for LiCoO ₂ are required.

Therefore, lithium manganese oxide (Li-Mn composite oxide), which is relatively cheaper than LiCoO ₂ and is excellent from an environmental point of view, has attracted attention. For example, Li-Mn composite oxides such as spinel type lithium manganate (LiMn ₂ O ₄ ) or orthorhombic type lithium manganate (LiMnO ₂ ) have been actively researched and developed as next-generation cathode active materials. ing.

  In the conventional manufacturing method, since Li-Mn composite oxides are all obtained in a powder state, in order to produce a positive electrode, a positive electrode active material slurry is prepared by adding a conductive material and a binder. This must be applied to a current collector such as an aluminum foil using an instrument such as a doctor blade and dried.

  However, when used in a drive source application for heavy industry such as an electric vehicle, a train, or an aircraft, charging and discharging with a very high current density is required. In secondary batteries used for such applications, it is desirable to increase the surface area of the positive electrode and make the positive electrode active material layer as thin as possible.

  Therefore, if a fiber electrode having electron conductivity is used as a current collector and a fiber electrode having an active material layer formed on the surface is used as a positive electrode as an electron transfer path, the surface area is larger than that of a conventional electrode. Thus, the current collecting property of the active material layer is also improved.

  The fiber electrode is produced by coating the surface of a thin fibrous material with a thin and uniform active material layer. The diameter of a single fiber electrode is about 100 μm at most, and it is possible to produce a considerably thin electrode compared to a conventional plate electrode, so that the charge / discharge rate of a secondary battery can be dramatically improved. It becomes possible. When a plurality of fiber electrodes having a diameter of several μm are laid in parallel to form a sheet-like electrode, it is possible to increase the density of the secondary battery compared to the case where an active material layer is formed on the surface of the metal foil. The battery capacity per unit volume of the secondary battery can be increased.

  Therefore, as disclosed in Patent Document 1, a fiber electrode having an electron conductive fibrous material as a current collector and a thin battery active material layer on its surface is used as an electron movement path. As a result, each of the powder particles can be brought close to the collected state, and an electrode having a larger surface area than the conventional one can be produced.

However, considering the mass production of fiber electrodes, it is not efficient to fabricate the electrodes one by one from a fiber with a diameter of about several μm. Therefore, depending on the size and application of the battery to be produced, In order to produce it, it is necessary to simultaneously convert hundreds to tens of thousands of fibers into electrodes. In Patent Document 2, a film made of a metal oxide or a transition metal oxide is formed in an annular shape on a carbon fiber, and then hydrothermally treated at 100 to 250 ° C. in a closed system using a solution containing lithium ions. Thus, a manufacturing method of a fiber positive electrode for a lithium secondary battery in which a positive electrode active material film of a Li-Mn composite oxide is formed is disclosed. In Patent Document 2, carbon fiber is used as a working electrode, platinum foil is used as a counter electrode, manganese nitrate aqueous solution is used as an electrolytic deposition bath, Mn ₃ O ₄ is electrolytically deposited on the surface of carbon fiber, and water is added using a lithium hydroxide aqueous solution. A fiber positive electrode for a lithium secondary battery whose surface is covered with a positive electrode active material film of a Li-Mn composite oxide such as LiMnO ₂ or LiMn ₂ O ₄ by heat treatment has been produced.

  On the other hand, a method for producing manganese oxide by electrolytic deposition is also known. Patent Document 3 discloses a method for producing electrolytic manganese dioxide by immersing carbon fiber in a manganese sulfate aqueous solution (electrolytic solution) and performing electrolysis.

JP 2003-317794 A International Publication No. 2010/089991 Pamphlet JP-A-2-213487

  As a method for forming a positive electrode active material film on the surface of carbon fiber, a method using an electrolytic deposition method disclosed in Patent Document 2 and a hydrothermal treatment using a lithium ion-containing aqueous solution includes a positive electrode active material and a binder. Compared with the method of applying the mixed slurry to the carbon fiber, it has an advantage that a thin and uniform positive electrode active material layer can be formed, and an improvement in high rate characteristics can be expected.

However, in the method of manufacturing a secondary battery for fiber cathode disclosed in Patent Document 2, although it is possible to form a film of LiMnO ₂ or LiMn ₂ O ₄ as a positive electrode active material on the carbon fiber surface, Li ₂ A film of MnO ₃ could not be formed, and there was room for improvement in the method of forming the positive electrode active material film.

Further, as a result of testing by the present inventors, Mn ₃ O ₄ sold as a reagent is hydrothermally treated with a lithium ion-containing aqueous solution to change Mn ₃ O ₄ to LiMnO ₂ that is a positive electrode active material. In this case, it was confirmed that Mn (OH) ₂ that does not contribute to the charge / discharge reaction remains.

Furthermore, as a result of the present inventors, it was tested, the MnO ₂ sold as a reagent, the by hydrothermal treatment using a lithium ion-containing aqueous solution, is possible to change the MnO ₂ in LiMnO ₂ as a positive electrode active material It was also confirmed that it was not possible.

The present invention, utilizing the electrolytic deposition, and an object thereof is to provide a lithium secondary battery fiber cathode manufacturing how to make Li ₂ MnO ₃ as a positive electrode active material.

The present invention aims to utilize the electrolytic deposition, the provision of Li ₂ MnO ₃ and LiMnO ₂ production how fiber cathode for a lithium secondary battery positive electrode active material.

The present inventors, as a result of intensive studies, using a manganese nitrate solution as electrolytic deposition bath, after the Mn ₃ O ₄ was electrolytically deposited on the carbon fiber surfaces, in the hydrothermal treatment step, the Mn ₃ O ₄ On the other hand, by using an electrolytic deposition bath containing a large excess of LiOH 40 times or more in moles, it becomes possible to efficiently dope lithium into Mn oxide, and Mn ₃ O ₄ can be converted to Li ₂ MnO _3. As a result, the present invention has been completed.

Specifically, the present invention
An electrolytic deposition process in which Mn (NO ₃ ) ₂ aqueous solution is used as an electrolytic deposition bath, carbon fiber is used as a working electrode, and Mn ₃ O ₄ is electrolytically deposited on the carbon fiber surface;
Hydrothermal treatment of the carbon fiber electrodeposited with Mn ₃ O ₄ in a LiOH aqueous solution to which an oxidizing agent is added, and a hydrothermal treatment step of changing Mn ₃ O ₄ to Li ₂ MnO ₃ ,
Have
The present invention relates to a method for producing a fiber positive electrode for a lithium secondary battery, wherein the amount of LiOH relative to the amount of Mn ₃ O ₄ in the hydrothermal treatment step is 40 times or more by mole.

An Mn (NO ₃ ) ₂ aqueous solution is used as the electrolytic deposition bath, and electrolytic deposition is performed using the carbon fiber as a working electrode, whereby Mn ₃ O ₄ is electrolytically deposited on the surface of the carbon fiber. In Patent Document 2, the amount of LiOH relative to the amount of Mn ₃ O ₄ in the hydrothermal treatment step is 3.5 times or less in terms of moles. In the present invention, hydrothermal treatment is performed using a large excess of LiOH that is 40 times or more. Thus, it is possible to transform Mn ₃ O ₄ into Li ₂ MnO ₃ .

  The counter electrode used at the time of electrolytic deposition is not particularly limited as long as the material has a function as a counter electrode. Specific examples of suitable counter electrodes are carbon materials such as carbon paper (carbon paper), carbon fibers (for example, filamentous, woven or non-woven fabric), carbon mat, and carbon plate.

By adding an oxidizing agent to the Mn (NO ₃ ) ₂ aqueous solution that is an electrolytic deposition bath, it becomes possible to oxidize all of Mn ₃ O ₄ to Li ₂ MnO ₃ , so that Li ₂ in the positive electrode active material film The MnO ₃ content can be increased.

The oxidizing agent is preferably H ₂ O ₂ . The number of moles relative to the amount of Mn ₃ O ₄ is preferably equal to or greater than the equivalent amount.

The present invention also provides
An electrolytic deposition process in which MnSO ₄ aqueous solution is used as an electrolytic deposition bath, carbon fiber is used as a working electrode, and MnO ₂ is electrolytically deposited on the carbon fiber surface;
Hydrothermal treatment of the carbon fiber electrodeposited with MnO ₂ in a LiOH aqueous solution, and hydrothermal treatment step of changing MnO ₂ into Li ₂ MnO ₃ and LiMnO ₂ ,
Have
The present invention relates to a method for producing a fiber positive electrode for a lithium secondary battery, wherein an amount of LiOH with respect to the amount of MnO ₂ in the hydrothermal treatment step is 40 times or more by mole.

According to the present invention, it is possible to stably manufacture a fiber positive electrode for a lithium secondary battery using Li ₂ MnO ₃ as a positive electrode active material.

  In addition, since a fiber cathode in which an active material layer is directly formed on a carbon fiber current collector can be manufactured, there is no need for a process of manufacturing an active material and converting it into an electrode as in the prior art. That is, the fiber cathode can be manufactured simultaneously with the manufacture of the active material.

  Therefore, in the fiber positive electrode obtained by the present invention, it is basically unnecessary to add a conductive additive or a binder to the active material film, and the slurrying and rolling steps of the active material are not required in the manufacturing process.

  Therefore, according to the present invention, mass production of the fiber positive electrode for a lithium secondary battery can be easily performed at low cost. In addition, the fiber positive electrode for a lithium secondary battery of the present invention does not require lithium doping in advance because the positive electrode active material contains lithium element. That is, the manufacturing process and the safety of the battery can be improved.

  In addition, since the carbon fiber current collector is a thin cylindrical conductive fiber, the active material film forms a closed ring when the active material film is formed on the carbon fiber. For this reason, the volume change accompanying charging / discharging is suppressed, and even when the expansion and contraction are repeated, the active material layer is less likely to be peeled off and dropped compared to the plate electrode. Furthermore, by bundling the carbon fibers, the carbon fibers are pressure-bonded to each other, which is more effective in preventing the active material film from falling off, and becomes a fiber positive electrode having a long life and excellent electrode characteristics.

The conceptual diagram explaining an electrolytic deposition process is shown. It is a graph showing the X-ray-diffraction result regarding Example 1, (a) is a fiber positive electrode precursor, (b) shows the XRD pattern of a fiber positive electrode. It is an electron micrograph of the fiber positive electrode regarding Example 1, (a) shows a fiber positive electrode precursor, (b) shows a fiber positive electrode. The charging / discharging curve of the lithium secondary battery of Example 1 in the constant current voltage 4.3V-3.2V is shown. It is a graph showing the X-ray-diffraction result regarding Example 2, (a) is a fiber positive electrode precursor, (b) shows the XRD pattern of a fiber positive electrode. Is a graph showing the X-ray diffraction results indicate a (a) Mn ₃ is a reagent O _4, (b) the XRD pattern of the powder thus obtained Mn ₃ O ₄ is a reagent after the hydrothermal treatment. It is a graph showing the X-ray-diffraction result regarding Example 3, (a) is a fiber positive electrode precursor, (b) shows the XRD pattern of a fiber positive electrode. The electron micrograph of the fiber positive electrode of Example 3 is shown. The charging / discharging curve of the lithium secondary battery of Example 3 in the constant current voltage 5.0V-2.0V is shown. Is a graph showing the X-ray diffraction results indicate a (a) Mn ₃ is a reagent O _4, (b) the XRD pattern of the powder thus obtained Mn ₃ O ₄ is a reagent after the hydrothermal treatment. The XRD pattern of the fiber positive electrode of Examples 3-6 is shown. The electron micrograph of the fiber positive electrode of Example 4 is shown. It is a graph showing the X-ray-diffraction result regarding Example 7, (a) shows a fiber positive electrode precursor, (b) shows the XRD pattern of a fiber positive electrode. It is a graph showing the X-ray diffraction results, (a) shows the MnO ₂ is a reagent, shows the (b) the XRD pattern of the powder obtained MnO ₂ is a reagent after the hydrothermal treatment. The electron micrograph of the fiber positive electrode precursor of Example 2 and Example 7, and a fiber positive electrode is shown.

Embodiments of the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the following description. Examples 1 and 4-6 are not included in the present invention.

[Example 1 / Fiber positive electrode for a lithium secondary battery in which a LiMn ₂ O ₄ film is formed as a positive electrode active material]
(Electrolytic deposition process)
A current collector was a carbon fiber bundle obtained by opening 12,000 commercially available carbon fibers (carbon fibers obtained by carbonizing polyacrylonitrile fiber from Toho Tenax Co., Ltd. at 2500 ° C.). The length of the carbon fiber constituting the current collector was 4 cm. The average fiber system of carbon fibers was 5 μm.

FIG. 1 is a conceptual diagram illustrating an electrolytic deposition process. As the electrolytic deposition bath, 60 mL of Mn (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4, 20 ° C.) was used, the above carbon fiber bundle was used for the working electrode 3, and carbon paper (Toray) was used for the counter electrodes 4a and 4b. Electrodeposition treatment using EC-CC1-060). The electrolytic deposition conditions were a current value of 0.1 A and an electrolytic deposition time of 20 minutes. As an electrolytic deposition apparatus, an electrochemical measurement system HZ-5000 (manufactured by Hokuto Denko Corporation) was used.

The carbon fiber after the electrolytic deposition treatment was washed with water and dried at 110 ° C. for 24 hours or more in an air atmosphere to obtain a fiber positive electrode precursor in which a Mn ₃ O ₄ film was formed on the carbon fiber surface. This fiber positive electrode precursor does not function as a positive electrode for a lithium secondary battery. Also in Examples 2 to 7 described later, the fiber positive electrode precursor does not function as a positive electrode for a lithium secondary battery.

(Hydrothermal process)
Next, 1 equivalent of Mn ₃ O ₄ formed on the surface of the carbon fiber was immersed in 30 equivalents of LiOH aqueous solution (LiOH concentration 3 mol / L) in the fiber cathode precursor and heated at 110 ° C. for 20 hours. Hydrothermal treatment was performed using an autoclave under the conditions. Thereafter, the carbon fiber was washed with water and dried under reduced pressure at 150 ° C. for 24 hours or more to obtain a fiber positive electrode (fiber positive electrode for a lithium secondary battery) having a LiMn ₂ O ₄ film formed as a positive electrode active material on the carbon fiber surface. .

<Analysis of crystal structure by X-ray diffraction>
The fiber positive electrode precursor and fiber positive electrode produced in Example 1 were subjected to X-ray diffraction. X-ray diffraction was performed using Cu-Kα rays (40 kV, 40 mA) in a 2θ measurement range of 10 ° to 90 °. The upper (a) of FIG. 2 shows the XRD diffraction pattern of the fiber positive electrode precursor of Example 1, and the lower (b) of FIG.

By performing hydrothermal treatment in an aqueous solution containing lithium ions, the diffraction peak of the fiber positive electrode of Example 1 shows a diffraction peak different from that of the fiber positive electrode precursor. When searching using JCPDS (Joint Committee on Powder Diffraction Standards), the diffraction pattern of (a) matches the pattern attributed to Mn ₃ O ₄ , so that the fiber cathode precursor has Mn _{3 on the} carbon fiber surface. It was confirmed that an O ₄ film was formed. On the other hand, both peaks of LiMn ₂ O ₄ and Mn ₃ O ₄ were observed in the diffraction pattern of (b). That is, it was confirmed that the film formed on the surface of the fiber positive electrode was LiMn ₂ O ₄ slightly mixed with Mn ₃ O ₄ .

3 is an electron micrograph of the fiber positive electrode precursor and the fiber positive electrode of Example 1, (a) shows the fiber positive electrode precursor, and (b) shows an electron micrograph of the fiber positive electrode. In the fiber positive electrode precursor of FIG. 3 (a), it was confirmed that flaky Mn ₃ O ₄ was formed on the carbon fiber surface by electrolytic deposition. In addition, it was confirmed that the fiber positive electrode in FIG. 3 (b) formed a porous aggregate in which flake-shaped particles were aggregated.

<Production of lithium secondary battery>
The fiber positive electrode of Example 1 (the length of the part where the active material film was formed was about 20 mm) was fixed to an Al lead wire with a width of about 20 mm. This positive electrode was sandwiched between two separators (thickness 0.44 mm, dimensions 40 mm × 50 mm glass filter), and the outside was sandwiched between lithium metal plates (thickness 0.5 mm, dimensions 25 mm × 30 mm). Thereafter, a bipolar aluminum laminate type using an electrolytic solution in which LiPF ₆ is dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 1. A lithium secondary battery was produced.

FIG. 4 shows a charge / discharge curve of the lithium secondary battery at a cutoff voltage of 4.3 to 3.2 V. A discharge capacity of 80 mAh g ⁻¹ was exhibited at 0.1 C discharge, and a utilization rate of 53% was obtained at 10 C discharge.

[Example 2 / Fiber cathode-1 for a lithium secondary battery in which a film composed of Li ₂ MnO ₃ and LiMnO ₂ is formed as a cathode active material]
The same fiber cathode precursor as in Example 1 was immersed in a fiber cathode precursor in 100 equivalents of LiOH aqueous solution (LiOH concentration 3 mol / L), with 1 equivalent of Mn ₃ O ₄ formed on the carbon fiber surface. Then, hydrothermal treatment was performed using an autoclave at 110 ° C. for 20 hours. Thereafter, the carbon fiber was washed with water and dried under reduced pressure at 150 ° C. for 24 hours or more to form a film composed of LiMnO ₂ and Li ₂ MnO ₃ as the positive electrode active material on the surface of the carbon fiber (for lithium secondary battery) Fiber positive electrode) was obtained. The fiber positive electrode of Example 2 was also subjected to X-ray diffraction under the same conditions as in Example 1.

FIG. 5 is a graph showing the X-ray diffraction results of Example 2, wherein (a) shows the same fiber cathode precursor as in Example 1, and (b) shows the XRD pattern of the fiber cathode. In the pattern of FIG. 5 (b), both peaks of Li ₂ MnO ₃ and LiMnO ₂ were observed, but no peak consistent with Mn ₃ O ₄ was observed. That is, it was confirmed that the film formed on the surface of the fiber positive electrode was Li ₂ MnO ₃ mixed with LiMnO ₂ .

Here, commercially available Mn ₃ O ₄ (manufactured by Kishida Chemical Co., Ltd., manganese trioxide (purity 98.0%)) was hydrothermally treated under the same conditions as in the hydrothermal treatment step of Example 2. After the hydrothermal treatment, the obtained powder was washed with water, and X-ray diffraction was performed on the powder dried at 110 ° C. for 24 hours or more in an air atmosphere under the same conditions as described above. FIG. 6 is a graph showing X-ray diffraction, in which (a) shows the XRD pattern of the powder obtained after hydrothermal treatment of the reagent Mn ₃ O ₄ and (b) the reagent Mn ₃ O ₄ .

In the pattern of FIG. 6 (b), a LiMnO ₂ peak was observed, but unlike the pattern of FIG. 5 (b), a Li ₂ MnO ₃ peak was not observed. Further, unlike the pattern of FIG. 5 (b), a peak of Mn (OH) ₂ was observed in the pattern of FIG. 6 (b). That is, it was confirmed that the reagent Mn ₃ O ₄ was not transformed into Li ₂ MnO ₃ even by hydrothermal treatment, and became LiMnO ₂ mixed with Mn (OH) ₂ .

[Example 3 / Fiber cathode for a lithium secondary battery in which a Li ₂ MnO ₃ film is formed as a cathode active material]
The same fiber positive electrode precursor as in Example 1 was prepared by adding 1 equivalent of Mn ₃ O ₄ formed on the surface of the carbon fiber in a 100 equivalent LiOH aqueous solution containing 1 equivalent of H ₂ O ₂ (LiOH concentration 3 mol / L). And hydrothermally treated under the same conditions as in Example 1. Thereafter, the carbon fiber was washed with water and dried under reduced pressure at 110 ° C. for 24 hours or more to obtain a fiber cathode in which a Li ₂ MnO ₃ film was formed on the carbon fiber surface as a cathode active material. The fiber positive electrode of Example 3 was also subjected to X-ray diffraction under the same conditions as in Example 1.

FIG. 7 is a graph showing the results of X-ray diffraction, where (a) shows the same fiber cathode precursor as in Example 1, and (b) shows the XRD pattern of the fiber cathode in Example 3. In the pattern of FIG. 7B, a Li ₂ MnO ₃ peak was observed, but unlike the pattern of FIG. 5B, no LiMnO ₂ peak was observed. That is, it was confirmed that the film formed on the surface of the fiber positive electrode of Example 3 was Li ₂ MnO ₃ .

  FIG. 8 shows an electron micrograph of the fiber positive electrode of Example 3. As shown in FIG. 8, in the fiber positive electrode of Example 3, spherical particles of about 400 nm were aggregated, and it was confirmed that the shape was greatly different from the fiber positive electrode of Example 1 shown in FIG. .

Using the fiber positive electrode of Example 3, a bipolar aluminum laminate type lithium secondary battery was produced in the same manner as in Example 1. FIG. 9 shows a charge / discharge curve (charge / discharge current 0.1 C) of the lithium secondary battery at a cutoff voltage of 5.0 to 2.0 V. The initial charge capacity of the fiber cathode of Example 3 is 235mAh g ^-1, the initial discharge capacity shows a 150 mAh g ^-1, initial irreversible capacity is shown by separation of Li ₂ O.

Mn ₃ O ₄ of the same reagent as above was hydrothermally treated under the same conditions as in Example 3. After the hydrothermal treatment, the obtained powder was washed with water, and X-ray diffraction was performed under the same conditions as in Example 1 for the powder dried in an air atmosphere at 110 ° C. for 24 hours or more. FIG. 10 is a graph showing X-ray diffraction results, where (a) shows the XRD pattern of the powder obtained after hydrothermal treatment of the reagent Mn ₃ O ₄ and (b) the reagent Mn ₃ O _4. .

The pattern of FIG. 10 (b) is almost the same as the pattern of FIG. 6 (b) in which the LiOH aqueous solution does not contain H ₂ O ₂ , and the Mn (OH) ₂ peak is recognized in addition to the LiMnO ₂ peak. It was. That is, it was impossible for Mn ₃ O _{4 as} a reagent to obtain Li ₂ MnO _{3 or} not to contain Mn (OH) ₂ even when H ₂ O ₂ was used in combination with hydrothermal treatment.

Example 4 / positive active material as _{Li [Ni X Li 1 / 3-2X} / 3 Mn 2/3-X / 3] O 2 fibers for lithium secondary battery coating is formed positive electrode -1]
As an electrolytic deposition bath, 45 mL of Mn (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C.) and 5 mL of Ni (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C.) A fiber positive electrode was obtained in the same manner as in Example 3 except that the mixed aqueous solution was used.

[Example 5 / Fiber cathode-2 for a lithium secondary battery in which a Li [Ni _X Li _{1 / 3-2X / 3} Mn _{2 / 3-X / 3} ] O ₂ coating is formed as a cathode active material]
As electrolytic deposition bath, 35 mL of Mn (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C) and 15 mL of Ni (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C) A fiber positive electrode was obtained in the same manner as in Example 3 except that the mixed aqueous solution was used.

[Example 6 / Fiber cathode-3 for a lithium secondary battery in which a Li [Ni _X Li _{1 / 3-2X / 3} Mn _{2 / 3-X / 3} ] O ₂ coating is formed as a cathode active material]
As electrolytic deposition bath, 25 mL of Mn (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C) and 25 mL of Ni (NO ₃ ) ₂ aqueous solution (0.3 mol / L, pH 4.0, 20 ° C) A fiber positive electrode was obtained in the same manner as in Example 3 except that the mixed aqueous solution was used.

About the fiber positive electrode of Examples 4-6, it carried out similarly to the fiber positive electrode of Example 3, and performed the X-ray diffraction. FIG. 11 shows the XRD patterns of the fiber positive electrodes of Examples 3 to 6. In the fiber cathodes of Examples 4 to 6 using an electrolytic deposition bath containing Ni (NO ₃ ) ₂ , the superlattice diffraction peak in which Li is regularly arranged in the fiber metal phase disappears, and Li and A peak of Li [Ni _X Li _{1 / 3-2X / 3} Mn _{2 / 3-X / 3} ] O ₂ which is a complex oxide of Mn and a peak of Ni (OH) ₂ were observed. In addition, since the proportion of the Ni (NO ₃ ) ₂ aqueous solution in the electrolytic deposition bath is smaller in Example 4 than in Examples 5 and 6, the Ni (OH) ₂ peak intensity is higher than that in Examples 5 and 6. It was confirmed that it was smaller than the peak intensity of (OH) ₂ .

  FIG. 12 shows an electron micrograph of the fiber positive electrode of Example 4. The fiber cathode shown in FIG. 12 has agglomerates of flaky particles having a thickness of about 200 nm, and the form differs greatly from the fiber cathode of Example 1 in FIG. 3 and Example 3 shown in FIG. Was confirmed.

[Example 7 / fiber cathode-2 for a lithium secondary battery in which a film composed of Li ₂ MnO ₃ and LiMnO ₂ is formed as a cathode active material]
(Electrolytic deposition process)
A mixed aqueous solution (pH 1.0) of 56 mL of MnSO ₄ aqueous solution (0.5 mol / L) and 28 mL of dilute sulfuric acid (0.5 mol / L) was used as the electrolytic deposition bath, with the working electrode 3 as the positive electrode and the counter electrodes 4a and 4b as the negative electrodes. A fiber positive electrode precursor was obtained in the same manner as in Example 2 except that the electrolytic deposition conditions were an electrolytic deposition time of 60 minutes and an electrolytic deposition temperature of 90 ° C. at a current value of 0.02 A.

(Hydrothermal process)
Next, this fiber positive electrode precursor was immersed in 100 equivalents of LiOH aqueous solution (LiOH concentration 3 mol / L) with 1 equivalent of MnO ₂ formed on the surface of the carbon fiber. And hydrothermally treated using an autoclave. Thereafter, the carbon fiber was washed with water and dried under reduced pressure at 150 ° C. for 24 hours or more to obtain a fiber positive electrode.

<Analysis of crystal structure by X-ray diffraction>
The fiber positive electrode precursor and fiber positive electrode produced in Example 7 were subjected to X-ray diffraction in the same manner as in Example 2. FIG. 13 is a graph showing the X-ray diffraction results of Example 7, wherein the upper (a) shows the fiber positive electrode precursor and the lower (b) shows the XRD pattern of the fiber positive electrode.

In the pattern of FIG. 13 (a), peaks of ε-MnO ₂ and γ-MnO ₂ were confirmed. On the other hand, both Li ₂ MnO ₃ and LiMnO ₂ peaks were observed in the pattern of FIG. 13 (b). That is, it was confirmed that the film formed on the surface of the fiber positive electrode was Li ₂ MnO ₃ slightly mixed with LiMnO ₂ .

Here, commercially available MnO ₂ (manufactured by Kishida Chemical Co., manganese dioxide (purity 99.9% or more)) was hydrothermally treated under the same conditions as in the hydrothermal treatment step of Example 7. After the hydrothermal treatment, the obtained powder was washed with water, and X-ray diffraction was performed on the powder dried at 110 ° C. for 24 hours or more in an air atmosphere under the same conditions as described above. FIG. 14 is a graph showing X-ray diffraction, in which (a) shows the XRD pattern of the powder obtained after hydrothermal treatment of the reagent MnO ₂ and (b) the reagent MnO ₂ .

The XRD pattern in FIG. 14 (b) is almost the same as the XRD pattern in FIG. 14 (a), and no peaks other than β-MnO ₂ were confirmed. That is, it was confirmed that MnO _{2 as} a reagent was not transformed into a positive electrode active material of a Li-Mn composite oxide even when H ₂ O ₂ was used in combination with hydrothermal treatment.

FIG. 15 shows electron micrographs of the fiber cathode precursor and the fiber cathode of Example 2 and Example 7. The fiber positive electrode precursor of Example 7 was confirmed to be denser in crystals than the fiber positive electrode precursor of Example 2. It was also confirmed that the LiMnO ₂ and Li ₂ MnO ₃ layers (films) obtained by the hydrothermal treatment became dense. As described above, the shape of the positive electrode active material of the Li-Mn composite oxide formed on the carbon fiber surface largely depends on the shape of the electrolytic deposit (Mn oxide) deposited on the carbon fiber surface in the electrolytic deposition process. Confirmed to do. By using an aqueous MnSO ₄ solution for the electrolytic deposition bath, it was possible to form a high-density Mn oxide film on the carbon fiber surface.

Lithium secondary battery fiber cathode manufacturing how the present invention is very useful in battery field.

1: Electrolytic deposition tank 2: Electrolytic deposition bath (electrolytic deposition solution)
3: Working electrode (bundle of carbon fibers)
4a, 4b: Counter electrode (carbon paper)

Claims (3)

An electrolytic deposition process in which Mn (NO ₃ ) ₂ aqueous solution is used as an electrolytic deposition bath, carbon fiber is used as a working electrode, and Mn ₃ O ₄ is electrolytically deposited on the carbon fiber surface;
Hydrothermal treatment of the carbon fiber electrodeposited with Mn ₃ O ₄ in a LiOH aqueous solution to which an oxidizing agent is added, and a hydrothermal treatment step of changing Mn ₃ O ₄ to Li ₂ MnO ₃ ,
Have
LiOH amount for Mn ₃ O ₄ content in the hydrothermal treatment step is not less than 40 times in moles, the production method of the fiber cathode for a lithium secondary battery. It said oxidizing agent is H ₂ O _2, a manufacturing method of a lithium secondary battery fiber cathode according to claim 1. An electrolytic deposition process in which MnSO ₄ aqueous solution is used as an electrolytic deposition bath, carbon fiber is used as a working electrode, and MnO ₂ is electrolytically deposited on the carbon fiber surface;
Hydrothermal treatment of the carbon fiber electrodeposited with MnO ₂ in a LiOH aqueous solution, and hydrothermal treatment step of changing MnO ₂ into Li ₂ MnO ₃ and LiMnO ₂ ,
Have
LiOH amount for MnO ₂ amount in the hydrothermal treatment step is not less than 40 times in moles, the production method of the fiber cathode for a lithium secondary battery.