JP3875053B2 - ELECTRODE MATERIAL, ITS MANUFACTURING METHOD, AND BATTERY USING THE SAME - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode material, a manufacturing method thereof, and a battery using the same.
[0002]
[Prior art]
The compounds generally called manganese dioxides include a wide range of oxides with an apparent valence of manganese ranging from trivalent to tetravalent, and are neutral such as various cations and water in addition to manganese and oxygen. Compounds having molecules in the structure are also included, and compounds having a very wide range of compositions and structures are known.
[0003]
Since manganese redox couples have a relatively high potential, these manganese dioxides have been studied and used as positive electrode materials for aqueous batteries, including dry batteries, and non-aqueous batteries, such as lithium ion batteries. Has been developed.
[0004]
In these manganese dioxides, many compounds are known in which the octahedron in which six oxygens are coordinated around manganese is used as a forming unit, and the octahedron has a structure in which faces, ridges, and vertices are connected together. Yes. Among them, there is a compound having a (2 × 2) tunnel structure, and as shown in FIG. 1, it has a tunnel surrounded by four sides in which two of the above-mentioned forming units are connected. FIG. 1 shows a case where the cation A ⁺ is contained in the tunnel.
[0005]
These compounds having a (2 × 2) tunnel structure are promising as an electrode material because the tunnel can be used as an ion transfer path, and actually used as an electrode material for a lithium battery or the like.
[0006]
[Problems to be solved by the invention]
However, since these compounds having a (2 × 2) tunnel structure have been conventionally produced using a hydrous compound obtained by a wet process using water, there is a drawback that the discharge capacity as an electrode is small. This is because the water molecules that entered the (2 × 2) tunnel during the manufacturing process are very stable, and even if this compound is dehydrated, it cannot be completely dehydrated. This is probably because protons adversely affect the electrode characteristics.
[0007]
The present invention solves the above-mentioned current problems, and is an manganese dioxide having a (2 × 2) tunnel structure as described above, which has a large discharge capacity, a manufacturing method thereof, and an electrode material thereof The object is to provide a battery using the battery.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention as described in claim 1,
An electrode material, which is a positive electrode material of a lithium battery, is represented by a composition formula Na _0.2 MnO ₂ , has a (2 × 2) tunnel structure, and does not contain protons and water in the tunnel Construct material.
[0009]
Further, the present invention provides the following, as described in claim 2.
A step of mixing sodium carbonate and manganese dioxide as starting materials , mixing the starting materials at a molar ratio of Na: Mn = 1: 5, and firing at 400 to 700 ° C. in an atmosphere with an oxygen partial pressure of 1 to 4 atm. The electrode material according to claim 1 is manufactured by a dry process that does not use water and has a manufacturing method of an electrode material.
[0010]
Further, the present invention provides a method as claimed in claim 3.
In an electrode material which is a positive electrode material of a lithium battery, the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 <z <0.4, y + z ≦ 0.4 and −0.2 ≦ δ ≦ 0) .2), and has a (2 × 2) tunnel structure, and constitutes an electrode material containing no proton and water in the tunnel .
[0011]
Further, the present invention provides the following, as described in claim 4.
A sodium compound and a manganese compound are used as starting materials and are produced by a dry process using no water, and are represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4 and −0.2 ≦ δ ≦ 0.2), (2 × 2) has a tunnel structure, a part of the sodium contained in the electrode material containing no protons and water into the tunnel, by ion-exchange treatment, by substituting lithium, the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 <z <0.4, y + z ≦ 0.4 and −0.2 ≦ δ ≦ 0.2), and has a (2 × 2) tunnel structure. And the electrode material which is a positive electrode material of the lithium battery which does not contain a proton and water in the said tunnel is obtained, and the manufacturing method of the electrode material characterized by the above-mentioned is comprised.
[0012]
Further, the present invention provides the following, as described in claim 5.
5. The method for producing an electrode material according to claim 4, wherein the ion exchange treatment is performed in a molten salt containing a lithium compound or in an organic solvent in which the lithium compound is dissolved. Constitute.
[0013]
Further, the present invention provides the following, as described in claim 6.
In the method for producing an electrode material according to claim 4, when the ion exchange treatment is performed in a molten salt, the ion exchange treatment is performed at a melting temperature of the molten salt of 400 ° C or higher, and when performed in an organic solvent, An electrode material manufacturing method is provided, which is performed while refluxing the solvent in the vicinity of the boiling point of the organic solvent .
[0014]
Further, the present invention provides the following, as described in claim 7.
In a lithium battery having a positive electrode, a negative electrode, and an electrolyte substance, the positive electrode is the electrode material according to claim 1 or 3, and the negative electrode uses lithium or a substance capable of reversibly inserting / extracting or occluding / releasing lithium. And the electrolyte substance is a non-aqueous electrolyte substance .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve this object, the electrode material according to the present invention has a composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) having a (2 × 2) tunnel structure. And a composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, having a (2 × 2) tunnel structure, It is characterized by being a compound represented by −0.2 ≦ δ ≦ 0.2).
[0016]
In addition, as a method for producing an electrode material according to the present invention, a sodium compound and a manganese compound are used as starting materials, and the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2) is performed by a dry process that does not use water. ≦ δ ≦ 0.2), a compound represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) By performing an ion exchange treatment, Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, −0.2 ≦ δ ≦ 0.2) It is characterized in that the ion exchange treatment is performed in the production of the compound represented, and in the molten salt containing the lithium-containing compound or in the organic solvent in which the lithium-containing compound is dissolved.
[0017]
The battery according to the present invention, the positive electrode has a negative electrode and an electrolyte material, wherein is characterized by containing an electrode material according to the present invention in the positive electrode, also, the negative electrode is Li Chiu arm or lithium Is formed using a substance that can be reversibly inserted / desorbed or occluded / released, and the electrolyte substance includes a substance capable of performing migration for causing lithium ions to electrochemically react with the positive electrode and the negative electrode. It is said.
[0018]
The present invention will be described in more detail.
[0019]
The inventor of the present application diligently searched for an electrode material having a (2 × 2) tunnel structure and having a large discharge capacity, and as a result, the discharge capacity of the battery is increased by using the above-described electrode material. In addition, the inventors have found that the above-described electrode material manufacturing method is effective in increasing the discharge capacity, and further confirmed that the discharge capacity of a battery using the electrode material is large, and completed the present invention based on this recognition. .
[0020]
A compound represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) having a (2 × 2) tunnel structure, which is an electrode material according to the present invention. The tunnel may contain a small amount of manganese, but in many cases it contains only sodium and is characterized by the absence of water or protons.
[0021]
Further, the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0,...) Having a (2 × 2) tunnel structure, which is an electrode material according to the present invention. 4, -0.2 ≦ δ ≦ 0.2) may contain a small amount of manganese, but in many cases contains only sodium and lithium, water and protons. The feature is that does not exist.
[0022]
When these compounds are used as electrode materials, it is considered that a large discharge capacity can be obtained because there are no water molecules or protons that adversely affect battery characteristics. In addition, since ions and molecules other than sodium and lithium do not exist between the tunnels, the molecular weight is relatively small and the energy density per weight is increased. Further, since the density (specific gravity) is higher than other manganese dioxides, there is an advantage that the energy density per volume is also large.
[0023]
When producing an electrode material which is a compound represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) according to the present invention, a sodium compound and Manganese compounds can be used as a starting material, and these can be produced by a dry process that does not use water, such as mixing and firing. If this compound is produced by such a dry process, it is possible to avoid the mixing of water into the (2 × 2) tunnel in the compound, and to avoid the mixing of water molecules and protons that adversely affect the battery characteristics. It has the advantage of being able to. For example, the above compound can be produced by mixing sodium carbonate and β-manganese dioxide (mineral name: pyrolsite) and reacting them in oxygen. Desirably, this compound is preferably produced at a temperature of 400 ° C. to 700 ° C. in an atmosphere where the oxygen partial pressure exceeds 1 atm.
[0024]
Also represented by the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, −0.2 ≦ δ ≦ 0.2) according to the present invention. The electrode material, which is a compound to be formed, is obtained by subjecting a compound represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) to an ion exchange treatment. Can be manufactured. That is, by the ion exchange treatment, sodium in the composition formula Na _x MnO _{2 + δ} is partially or entirely replaced with lithium, and the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z < 0.4, y + z ≦ 0.4, −0.2 ≦ δ ≦ 0.2).
[0025]
In this case, it is preferable to perform an ion exchange treatment in a molten salt containing a lithium-containing compound or in an organic solvent in which the lithium-containing compound is dissolved. Considering the characteristic that the electrode material easily absorbs water, it is desirable to perform ion exchange in these non-aqueous environments. As the molten salt, a molten salt containing at least one of lithium nitrate, lithium chloride, lithium bromide, and lithium iodide can be used. In addition, ion exchange can be performed in an organic solvent in which a lithium-containing compound such as lithium chloride or lithium bromide is dissolved. In ion exchange, since the ion exchange rate increases as the amount of ion species that can be exchanged increases, it is particularly preferable to use a molten salt obtained by directly melting a lithium compound. Further, since the exchange rate is higher as the temperature is higher, it is preferable to perform ion exchange at a high temperature in order to exchange sodium for as much lithium as possible in a short time. However, if the temperature is higher than necessary, the produced compound may be decomposed, so it is preferable to carry out at a temperature of 400 ° C. or lower. Needless to say, when a molten salt is used, the reaction temperature must be equal to or higher than the melting point of the molten salt. When ion exchange is performed in an organic solvent, it is preferable to perform ion exchange while refluxing the solvent near the boiling point of the organic solvent in order to increase the ion exchange rate.
[0026]
In the above composition formula, x, y, z, and δ are 0 <x ≦ 0.4, 0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, and −0.2 ≦, respectively. Although δ ≦ 0.2 is satisfied, these vary depending on the synthesis conditions. The compound represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) has a (2 × 2) tunnel structure in the vicinity of x = 0.2. Since a compound is easily obtained, x = 0.2 is preferable. Further, a compound represented by ion-exchanged Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, −0.2 ≦ δ ≦ 0.2). In this case, it is normal that sodium in the starting material is eliminated by an amount y containing lithium (xy = z). However, since the valence of manganese can change depending on the reaction conditions, the starting material The sum of the amount of sodium x, the amount of sodium y and the amount of lithium z of the product may not be equal. In addition, oxygen may enter and exit during ion exchange, and the δ value may change.
[0027]
When the electrode material according to the present invention is used in a battery in which lithium ions move, it is preferable to increase the y value and decrease the z value. This is because the presence of many lithium ions, which are ion species that move, in the (2 × 2) tunnel facilitates ion diffusion in the electrode material and provides a large capacity.
[0028]
In order to form a positive electrode including the electrode material according to the present invention, a mixture of the electrode material and a binder powder such as polytetrafluoroethylene is pressure-formed on a support such as stainless steel. Alternatively, in order to impart conductivity to the active material powder, a conductive powder such as acetylene black is mixed, and a binder powder such as polytetrafluoroethylene is added to the active powder as required. The positive electrode is formed by such means as placing the mixture in a metal container, pressure forming on a support such as stainless steel, or dispersing the mixture in a solvent such as an organic solvent to form a slurry and applying it onto a metal substrate.
[0029]
The battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte substance, and the positive electrode is configured using the electrode material according to the present invention. The Li Chiu arm or the negative electrode is constituted by using a material capable of reversibly insertion and extraction or absorbing and desorbing lithium, the electrolyte material, for ions of lithium to the positive electrode and the negative electrode and the electrochemical reaction The battery contains a substance that can move, and this battery functions as a battery by lithium ions moving back and forth between the positive electrode and the negative electrode.
[0030]
As described above, when a substance containing lithium is used as the negative electrode, a conventionally known material such as a lithium metal, a lithium-aluminum alloy, a lithium-carbon compound, or a lithium-containing nitride is used as such a substance. be able to.
[0031]
Examples of the electrolyte substance include methoxyethane, diethoxyethane, 2-methyltetrahydrofuran, ethylene carbonate, propylene carbonate, methyl formate, dimethyl sulfoxide, acetonitrile, butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, and ethyl. A non-aqueous electrolyte solvent in which a salt such as an alkali metal or alkaline earth metal is dissolved in an organic solvent such as methyl carbonate, a solid electrolyte, a polymer electrolyte, a polymer electrolyte in which the organic solvent is supported, or the like can be used.
[0032]
In addition, the battery can be used as a secondary battery by repeatedly discharging and charging the battery.
[0033]
Furthermore, conventionally known various materials can be used for other elements such as a structural material such as a separator and a battery case, and there is no particular limitation.
[0034]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0035]
[Example 1]
FIG. 2 is a cross-sectional view of a coin-type battery which is a specific example of a battery using manganese dioxide having a (2 × 2) tunnel structure manufactured by the manufacturing method according to the present invention as a positive electrode active material. 1 is a sealing plate, 2 is a gasket, 3 is a positive electrode case, 4 is a negative electrode, 5 is a separator, and 6 is a positive electrode mixture pellet.
[0036]
In this example, sample a produced as follows was used as the positive electrode active material. Sodium carbonate and β-manganese dioxide (mineral name: pyrolsite) are mixed at a molar ratio of Na: Mn = 1: 5 in an atmosphere having an oxygen partial pressure of 4 atm. A sample a having the composition Na _0.20 MnO ₂ was obtained by heat treatment.
[0037]
The sample a thus produced was analyzed using a powder X-ray diffraction measurement method. As shown in FIG. 3, the sample a was in good agreement with JCPDS (Joint Committee on Powder Diffraction Standards) data, and (2 × 2 It was found to have a tunnel structure. That is, the sample a is represented by a composition formula Na _x MnO _{2 + δ} (where 0 <x ≦ 0.4, −0.2 ≦ δ ≦ 0.2) and has a (2 × 2) tunnel structure. It is one of electrode materials characterized by being a compound. In this case, the structure of the sample a is shown in FIG. 1, and A ^{+ in} the figure corresponds to Na ⁺ .
[0038]
The above-described process for obtaining the sample a is a dry process that does not use water.
[0039]
Next, this sample a was subjected to an ion exchange treatment in a 3: 1 molar molten salt of lithium nitrate and lithium chloride. The amount of sample a in the molten salt was a molar ratio: Li in the molten salt: Na in the sample a = 20: 1, and the temperature of the molten salt was 350 ° C. This ion exchange treatment was performed three times, and the obtained solid was washed with methanol and dried to obtain a sample b. The chemical composition of the sample b was analyzed, and Li _0.10 Na _0.10 MnO ₂ was obtained as a composition formula.
[0040]
When the sample b thus produced was analyzed using a powder X-ray diffraction measurement method, as shown in FIG. 4, since the same pattern as that of the sample before ion exchange was maintained, (2 × 2 It was found to have a tunnel structure. That is, the sample b has the composition formula Li _y Na _z MnO _{2 + δ} (where 0 <y ≦ 0.4, 0 ≦ z <0.4, y + z ≦ 0.4, −0.2 ≦ δ ≦ 0.2). And (2 × 2) one of electrode materials characterized by being a compound having a tunnel structure. In this case, the structure of the sample b is shown in FIG. 1, and A ^{+ in} the figure corresponds to Li ⁺ or Na ⁺ .
[0041]
The powder of sample a or sample b was mixed with a conductive agent (acetylene black) and a binder (polytetrafluoroethylene), and then roll-formed to form positive electrode mixture pellets 6 (thickness 0.5 mm, diameter 15 mm) did.
[0042]
Next, a metal lithium negative electrode 4 placed under pressure on a stainless sealing plate 1 is inserted into the recess of the polypropylene gasket 2, and a polypropylene microporous separator 5 and a positive electrode composite are placed on the negative electrode 4. The electrolyte pellet 6 is arranged in this order, and an electrolyte solution that is an electrolyte substance that enables lithium ions to move electrochemically with the positive electrode and the negative electrode is used as an equal volume mixed solvent of ethylene carbonate and dimethyl carbonate. A suitable amount of 1N solution in which LiPF ₆ was dissolved was injected and impregnated, and then covered with a stainless steel positive electrode case 3, and then a coin-type battery having a thickness of 2 mm and a diameter of 23 mm (in FIG. Inverted) was prepared.
[0043]
A battery using the sample a or the sample b thus produced as a positive electrode active material was charged to 4.5 V at a current density of 0.1 mA / cm ² and then discharged to 2.0 V. Then, it was possible to obtain a capacity of 160 mAh / g for sample a and 180 mAh / g for sample b. Therefore, it can be seen that a battery having a large discharge capacity can be realized by using an electrode material having a (2 × 2) tunnel structure manufactured by the manufacturing method according to the present invention.
[0044]
[Comparative Example 1]
In this comparative example, a lithium battery was produced in the same manner as in Example 1 except that the sample c produced as follows was used according to a conventional wet method.
[0045]
First, manganese nitrate and sodium permanganate are mixed at a molar ratio of 1: 1 in dilute sulfuric acid, reacted at 100 ° C. for 5 hours, and the powder produced in the solution is separated from the solution by filtration and dried at 100 ° C. Sample c was obtained.
[0046]
When the sample c thus produced was analyzed using a powder X-ray diffraction measurement method, a pattern similar to the sample a was obtained, and it was found that the sample c had a (2 × 2) tunnel structure.
[0047]
2 Sample c thus produced by the cell to the cathode active material prepared in the same manner as in Example 1, the battery after the charging to 4.5V at a current density of 0.1 mA / cm ^2. Even when discharged to 0 V, only a capacity of 120 mAh / g was obtained. As compared with this battery, it can be seen that the battery including the sample manufactured in Example 1 of the present invention as the positive electrode active material has a larger discharge capacity.
[0048]
The reason why the capacity of the battery in this comparative example is smaller than the capacity of the battery of Example 1 is considered to be due to the adverse effect of water molecules present in the (2 × 2) tunnel structure of sample c on the electrode characteristics. .
[0049]
As described above, the manufacturing method of a manganese dioxide electrode material having a (2 × 2) tunnel structure according to the present invention, and the manganese dioxide electrode material having a (2 × 2) tunnel structure manufactured by the method are provided. According to the battery included as the positive electrode, a battery having a large discharge capacity can be realized, and the present invention has a point that it can be used in various fields including a power source of various electronic devices.
[0050]
【The invention's effect】
By carrying out the present invention, it is possible to provide an electrode material having a large discharge capacity, which is a manganese dioxide having a (2 × 2) tunnel structure, a manufacturing method thereof, and a battery using the electrode material.
[Brief description of the drawings]
FIG. 1 is a structural schematic diagram of an electrode material according to the present invention.
FIG. 2 is a cross-sectional view showing a configuration example of a coin-type battery in Example 1 of the present invention.
FIG. 3 is a diagram showing a comparison of the X-ray diffraction pattern of sample a in Example 1 of the present invention identified by powder X-ray diffraction measurement and the peak data of manganese dioxide having a (2 × 2) tunnel structure by JCPDS. It is.
FIG. 4 is a diagram showing an X-ray diffraction pattern of sample b in Example 1 of the present invention identified by powder X-ray diffraction measurement, compared with sample a before ion exchange.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Sealing plate, 2 ... Gasket, 3 ... Positive electrode case, 4 ... Negative electrode, 5 ... Separator, 6 ... Positive electrode mixture pellet.

Claims (7)

An electrode material, which is a positive electrode material of a lithium battery, is represented by a composition formula Na _0.2 MnO ₂ , has a (2 × 2) tunnel structure, and does not contain protons and water in the tunnel material. A step of mixing sodium carbonate and manganese dioxide as starting materials , mixing the starting materials in a molar ratio of Na: Mn = 1: 5, and firing at 400 to 700 ° C. in an atmosphere with an oxygen partial pressure of 1 to 4 atm. having, by a dry process without using water, a manufacturing method of an electrode material, characterized by manufacturing an electrode material according to claim 1. In an electrode material which is a positive electrode material of a lithium battery, the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 <z <0.4, y + z ≦ 0.4 and −0.2 ≦ δ ≦ 0) .2), an electrode material having a (2 × 2) tunnel structure and containing no proton and water in the tunnel . A sodium compound and a manganese compound are used as starting materials and are produced by a dry process using no water, and are represented by the composition formula Na _x MnO _{2 + δ} (0 <x ≦ 0.4 and −0.2 ≦ δ ≦ 0.2), (2 × 2) has a tunnel structure, a part of the sodium contained in the electrode material containing no protons and water in the tunnel, by ion-exchange treatment, by substituting lithium, the composition formula Li _y Na _z MnO _{2 + δ} (0 <y ≦ 0.4, 0 <z <0.4, y + z ≦ 0.4 and −0.2 ≦ δ ≦ 0.2), and has a (2 × 2) tunnel structure. And the electrode material which is a positive electrode material of the lithium battery which does not contain a proton and water in the said tunnel is obtained, The manufacturing method of the electrode material characterized by the above-mentioned . 5. The method for producing an electrode material according to claim 4, wherein the ion exchange treatment is performed in a molten salt containing a lithium compound or an organic solvent in which the lithium compound is dissolved. In the method for producing an electrode material according to claim 4, when the ion exchange treatment is performed in a molten salt, the ion exchange treatment is performed at a melting temperature of the molten salt of 400 ° C or higher, and when performed in an organic solvent, A method for producing an electrode material, which is carried out while refluxing the solvent near the boiling point of the organic solvent . In a lithium battery having a positive electrode, a negative electrode, and an electrolyte substance, the positive electrode is the electrode material according to claim 1 or 3, and the negative electrode uses lithium or a substance capable of reversibly inserting / extracting or occluding / releasing lithium. And the electrolyte substance is a non-aqueous electrolyte substance .

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