JP4636642B2 - Spinel type lithium manganese composite oxide and method for producing the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a spinel-type lithium-manganese composite oxide, and in particular, is used as a positive electrode material or a lithium adsorbent precursor for a 3V class lithium secondary battery in which the structure of the spinel-type composite oxide is Li ₄ Mn ₅ O _12. A spinel type lithium manganese oxide and its manufacturing method are proposed.
[0002]
[Prior art]
In recent years, against the backdrop of miniaturization and high performance of electronic devices, the production volume of lithium ion secondary batteries has increased rapidly due to the rapid spread of mobile phones in particular. The main reason for the rapid spread of lithium ion secondary batteries is that the electromotive force is about three times higher than that of secondary batteries such as nickel metal hydride batteries, which contributes to weight reduction of mobile phones and the like.
[0003]
Recently, spinel-type lithium manganese composite oxides have been developed as a positive electrode material for such lithium ion secondary batteries in consideration of resources, safety, and the like.
As such composite oxides, spinel type composite oxides such as LiMn ₂ O ₄ , Li ₂ Mn ₄ O ₉ and Li ₄ Mn ₅ O ₁₂ and non-spinel type LiMnO ₂ composite oxides are known. Among these lithium manganese spinel complex oxides, spinel complex oxides having a structural formula of LiMn ₂ O ₄ are used in lithium secondary batteries as 4V class positive electrode materials.
[0004]
On the other hand, the spinel-type composite oxide having a constitutive formula of Li ₄ Mn ₅ O ₁₂ theoretically shows a discharge capacity of about 163 mAh / g, and despite the fact that the discharge capacity is larger than that of LiMn ₂ O ₄ , the lithium It has never been used as a positive electrode material for a secondary battery. This is because it easily changes to another composite oxide depending on the firing conditions.
[0005]
That is, when Li ₄ Mn ₅ O ₁₂ composite oxide is baked at a temperature of 450 ° C. or higher, oxygen defects are generated and change to another composite oxide structure, and when baked at a temperature of 500 ° C. or higher, Li ₄ Mn ₅ It decomposes into a compound of O _12- δ or LiMn ₂ O ₄ and Li ₂ MnO ₃ . However, if it is fired at a low temperature of about 300 ° C., it is difficult to produce a spinel composite oxide having a Li ₄ Mn ₅ O ₁₂ structure.
[0006]
As described above, the Li ₄ Mn ₅ O ₁₂ composite oxide is different from the structure (form) of the composite oxide to be produced even if the firing temperature is slightly different, or is another composite oxide having many oxygen defects. Therefore, sufficient discharge capacity and discharge characteristics cannot be obtained. In short, the complete spinel type complex oxide of Li ₄ Mn ₅ O ₁₂ structure was difficult to produce under the state of the art, so that it could not be used as a positive electrode material for secondary batteries. It is thought that.
[0007]
[Problems to be solved by the invention]
Conventionally, as a positive electrode material for a 3V class secondary battery, a manganese dioxide fired material obtained by firing MnO ₂ at a low temperature, a mixture of Li ₂ MnO ₃ and manganese dioxide, or the like has been used. However, these positive electrode materials have a problem that the charge / discharge capacity after two cycles is rapidly decreased, the discharge capacity is as low as 100 mAh / g, and the potential difference between the initial discharge capacity and the final discharge capacity is large. In particular, it was necessary to improve the discharge characteristics.
Conventionally, various techniques have been proposed to improve the above-described problems. For example, the invention described in Japanese Patent Application Laid-Open No. 4-253161 is an example thereof, and after MnO ₂ and a lithium salt are reacted in an alkali, heat treatment is performed in a temperature range of 150 ° C. to 300 ° C. under reduced pressure. Thus, lithium manganese oxide is obtained.
Although this known technique has improved the discharge capacity characteristics, it is still insufficient.
[0008]
As another proposal, when recovering lithium, which is a scarce resource, from seawater, etc., as a substance for recovering the lithium, after mixing and burning lithium in the above MnO ₂ , only lithium is removed and micropores are removed. There is a method using a manganese oxide in which is formed. However, the lithium adsorbent composed of such a manganese oxide has a problem that the adsorbed amount is not so high as about 10 mg / g (lithium adsorbed amount per 1 g of adsorbent) and the stability against acid is low.
[0009]
An object of the present invention is to provide a lithium secondary battery positive electrode material having a potential of 3V class by using a high charge / discharge capacity of a spinel type composite oxide having a Li ₄ Mn ₅ O ₁₂ structure. The purpose is to increase the capacity and to improve the potential flatness of the 3V class secondary battery.
Another object of the present invention is to provide a lithium adsorbent having improved lithium adsorption performance and excellent structural stability by using a spinel-type composite oxide having a Li ₄ Mn ₅ O ₁₂ structure as a precursor for lithium adsorption. There is to do.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the inventors have conceived the present invention by focusing on synthesizing a Li ₄ Mn ₅ O ₁₂ composite oxide having a spinel structure by a liquid phase synthesis method (self-combustion method). According to the present invention, a spinel type lithium manganese composite oxide having a composition formula: Li ₄ Mn ₅ O ₁₂ having a lattice constant of 8.160 to 8.130 Å can be produced. Such a composite oxide can be used as a precursor for a lithium adsorbent in addition to being used as a positive electrode material for a 3V class lithium secondary battery .
[0011]
The method for producing a composite oxide according to the present invention comprises a mixed aqueous solution obtained by mixing Li nitrate and Mn nitrate so as to generate Li ₄ Mn ₅ O ₁₂ in a stoichiometric manner. without nonionic water-soluble polymer was added and mixed as a cation carrier, then the composition formula lattice constant by heating removing moisture is 8.160~8.130Å: Li ₄ spinel-type lithium manganese complex oxide of Mn ₅ O ₁₂ It synthesizes things.
[0012]
In the above invention, it is preferable that the water is removed by heating in a temperature range of 100 to 200 ° C., and after the heat removal of the water, the temperature is further 400 ° C. or higher and lower than the decomposition temperature of the Li ₄ Mn ₅ O ₁₂ composite oxide. It is preferable to perform the heat treatment again in the temperature range.
[0013]
In the above production method, as the nonionic water-soluble polymer, it is desirable to use a polymer compound having an OH group which is an organic substance that is easily nitrated.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The feature of the present invention is to propose a technique for industrially producing a Li ₄ Mn ₅ O ₁₂ based composite oxide having a lattice constant of 8.160 Å or less, preferably 8.150 to 8.130 Å, more preferably 8.150 to 8.140 Å. It is in. Such a complex oxide exhibits an initial discharge capacity characteristic of 150 mAh / g or more as a 3V class positive electrode material, and is excellent in potential flatness and cycle characteristics.
Moreover, such a Li ₄ Mn ₅ O ₁₂ system complex oxide as the lithium adsorbent in seawater (pH 7-8), is used as a precursor of the lithium adsorbent capable of obtaining an adsorption amount of more than 30 mg / g be able to.
In addition, the spinel type complex oxide of the present invention can be used by being mixed with a positive electrode material for a 4V class lithium battery as well as a 3V class positive electrode material.
[0016]
With respect to the composite oxide according to the present invention, in particular, when the X-ray lattice constant is 8.160 Å or less, the valence number of manganese in the composite oxide is approximately tetravalent. If the valence number of manganese is tetravalent, a composite oxide having an initial discharge capacity characteristic of 150 mAh / g or more, excellent potential flatness and good cycle characteristics can be obtained. However, if the lattice constant exceeds 8.160Å, trivalent manganese increases, and if it is less than 8.130Å, a composite oxide such as Li ₂ MnO ₃ is formed. Cannot be obtained.
[0017]
The lithium manganese composite oxide exhibiting the above-described characteristics is manufactured by applying a liquid phase synthesis method (self-reaction method). The feature of this method is that lithium and manganese nitrates and nonionic water-soluble polymers are added as a cation carrier, mixed, and then heated to remove moisture at a relatively low temperature to cause self-reaction. This is to synthesize a composite oxide.
[0018]
In this method, if the heating temperature is less than 80 ° C., decomposition and combustion of the nitro compound do not occur and a composite oxide cannot be synthesized. On the other hand, since the upper limit of the temperature may be any temperature at which moisture evaporates and the nitro compound decomposes, it is desirable that the upper limit of the temperature be in the range of 450 ° C. or less depending on the type of water-soluble polymer used. More preferably, the temperature range of 100-200 degreeC is good. This is because when heat baking is performed at a high temperature exceeding 450 ° C., oxygen defects occur and the battery performance deteriorates. If it is fired at a temperature exceeding 500 ° C., it is decomposed into Li ₄ Mn ₅ O ₁₂ or a composite oxide of LiMnO ₂ and LiMn ₂ O ₄ .
[0019]
By heating in the above temperature range, two or more kinds of cations in the mixed aqueous solution are fixed in a state of being uniformly mixed with the cation carrier as the moisture evaporates. On the other hand, nitrate ions react with heat with a cation carrier to produce a nitro compound. As a result, when the heating is continued, the nitro compound is burnt and decomposed, and cations react with each other by the thermal energy to synthesize a composite oxide.
[0020]
The composite oxide powder thus obtained is a fine powder having a large specific surface area. However, the oxide powder immediately after synthesis contains C and N as impurities, and it may be desirable to remove these impurities.
[0021]
Next, it is effective that the composite oxide according to the present invention is subjected to reheating treatment (firing) in a high temperature region in addition to the above-described composite oxide synthesis process. Such reheat treatment is desirably performed in a temperature range of 400 ° C. or higher and lower than the decomposition temperature of the composite oxide.
[0022]
The reason why the reheating temperature is limited is that distortion is left in the crystal arrangement only by heating at a relatively low temperature (100 ° C. to 200 ° C.). Therefore, in order to eliminate such crystal distortion and defects and to obtain a composite oxide that is almost completely crystallized, the above-described reheating treatment at a high temperature is required.
[0023]
In the production method according to the present invention, the reason why nitrates of Li and Mn are used is that nitrate ions can react with a nonionic polymer that is a cation carrier to generate a nitro compound, and at low temperatures. This is because it easily decomposes, so that the remaining product can be easily removed as compared with other anions (sulfate ion, chlorine ion, etc.).
As an example of the Li nitrate, LiNO ₃ is preferable, and as the Mn nitrate, Mn (NO ₃ ) ₂ .6H ₂ O is preferable.
[0024]
In addition, in the production method according to the present invention, the reason for using a cation carrier is that if the cation carrier is not added, nitrates of each element are separated and precipitated due to the difference in solubility due to moisture evaporation in the mixed aqueous solution by heating. Because it will end up.
This cation carrier is a substance having a function of supporting and fixing a cation, and may be any nonionic water-soluble polymer that does not contain metal ions. For example, starch such as wheat starch, mannan (konjac, etc.), Seaweeds such as agar (agar), plant mucilages such as troroaoy and gum arabic, mucilage due to microorganisms such as dextran, natural polymers such as glue and gelatin, proteins such as viscose and methylcellulose (MC) There are cellulosic products, semi-synthetic products represented by starch systems such as soluble starch and dialdehyde starch, and synthetic products represented by polyvinyl alcohol (PVA). Especially, it is preferable to use 1 or more types chosen from PVA, MC, agar, etc. which have an OH group with the organic substance which is easy to nitrate.
[0025]
In the production method according to the present invention, the reason for using a nonionic water-soluble polymer that does not contain metal ions is that if metal ions such as potassium and sodium remain, they are incorporated into the crystal structure of the desired composite oxide. Or a new compound is produced.
[0026]
The lithium manganese composite oxide according to the present invention thus produced is considered to be synthesized based on the following reaction mechanism.
{Circle around (1)} First, the cations in the mixed nitrate aqueous solution of lithium and manganese are gradually supported and fixed on the cation support as the moisture evaporates due to heating, and are in a uniform state that is easy to react.
(2) On the other hand, nitrate ions in the mixed nitrate aqueous solution react with the cation carrier by heating to produce a nitro compound.
(3) The nitro compound carrying the cation decomposes and burns upon further heating and generates heat. The heat energy at this time causes cations to react with each other to synthesize a spinel-type lithium manganese composite oxide.
[0027]
【Example】
(Example 1)
The composite oxide according to this example is produced by applying a liquid phase synthesis method to Li ₄ Mn ₅ O ₁₂ used as an electrode material for a 3V class lithium battery.
In this method, LiNO ₃ : 0.133 mol and Mn (NO ₃ ) ₂ .6H ₂ O: 0.167 mol were first dissolved in 10 ml of pure water to obtain a mixed aqueous solution. After adding 33 g of a 20% PVA solution as a cation support to the mixed aqueous solution, the mixture was transferred to a dryer and dried by heating at 150 ° C. for 2 hours to obtain a black powder. When the powder was identified by X-ray diffraction, it was confirmed that it was a Li ₄ Mn ₅ O ₁₂ single phase.
Furthermore, after the above heat drying, baking was performed at a temperature of 450 ° C. for 5 hours, and the powder was identified by X-ray diffraction. As a result, the X-ray lattice constant was 8.145 Å, and the desired Li ₄ Mn ₅ O ₁₂ was obtained. (See FIG. 1).
[0028]
(Comparative Example 1)
For comparison, Li ₂ CO ₃ powder (0.0665 mol, particle size 2 μm) and MnO ₂ powder (0.167 mol, particle size) are made to have the same target composition as in Example 1 by the conventional powder sintering method (solid phase method). The mixture was stirred and mixed with a stirrer for 1 hour, and then fired in a firing furnace at 450 ° C. for 5 hours to obtain a lithium / manganese / nickel composite oxide.
When the obtained powder was identified by X-ray diffraction, it was a spinel structure of lithium manganese, but the target single phase of Li ₄ Mn ₅ O ₁₂ was not obtained, and the X-ray lattice constant was 8.170 Å. It was found that the spinel composite oxide had low crystallinity.
[0029]
(Example 2)
A secondary battery characteristic test was conducted using the powder obtained in Example 1 and the powder obtained in Comparative Example 1 as a positive electrode material.
The battery characteristics were evaluated using a tripolar system using the positive electrode material of Example 1 and Comparative Example 1 as the positive electrode, metallic lithium as the negative electrode and the reference electrode, and ethylene carbonate and dimethyl carbonate containing 1M lithium perchlorate as the electrolyte. Performed in a glass cell. The measurement voltage range was 2.0 to 3.5 V, and the charge / discharge rate was 0.1 C.
[0030]
In order to evaluate the manufactured battery, a charge / discharge cycle test was performed. FIG. 2 shows the result of the positive electrode material manufactured under the method suitable for the present invention, and FIG. 3 shows the result of the composite oxide of the comparative example. As can be seen from FIG. 2, the discharge capacity of the composite oxide according to the present invention, of the initial charge-discharge capacity in the range of about 150 mAh / g, the discharge capacity of the composite oxide according to the comparative example, shown in FIG. 3 Thus, the initial charge / discharge capacity is about 40 mAh / g, and it can be seen that the spinel single-phase defects (existence of other complex oxides) and the presence of crystal defects affect the discharge capacity. Further, spinel composite oxide of the present invention from FIG. 2, the discharge capacity of the second represents the first time and the same performance, the discharge capacity by repeated charging and discharging was confirmed that no decrease.
[0031]
(Example 3)
The composite oxide of the present invention according to this example is Li ₄ Mn ₅ O ₁₂ used as a Li ₄ Mn ₅ O ₁₂ lithium adsorbing material.
First, LiNO ₃ : 0.133 mol and Mn (NO ₃ ) ₂ · 6H ₂ O: 0.167 mol were dissolved in 10 ml of pure water to obtain a mixed aqueous solution. After adding 33 g of a 20% solution of PVA as a cation carrier to this mixed aqueous solution, it was transferred to a dryer and dried by heating at 150 ° C. for 2 hours. As a result, a black powder was obtained. When this was identified by X-ray diffraction, it was confirmed that it was a Li ₄ Mn ₅ O ₁₂ single phase.
The heating and drying after the further and re-heated and fired for 5 hours at a temperature 450 ° C., as a result of reheating baked powder was identified by X-ray diffraction, X-ray lattice constant indicates 8.145 Å, higher crystallinity Li ₄ It was confirmed that Mn ₅ O ₁₂ (the lithium adsorbent precursor of the present invention) was obtained.
5 g of this calcined raw material (precursor for lithium adsorbent) is immersed in 100 ml of 1 mol / l HCl to perform ion exchange between lithium and hydrogen, and then dried in a dryer at 60 ° C. for 12 hours to adsorb lithium. An agent was obtained.
0.03 g of the obtained lithium adsorbent was immersed in 50 ml of a lithium solution adjusted to a lithium concentration of 70 ppm and pH 8.1 and held for 24 hours to adsorb lithium. When the adsorbed lithium ions were measured, it was found that the adsorbed amount was 30 mg-Li / g-adsorbent.
[0032]
For comparison, the lithium manganese composite oxide produced by the method of Example 2 was treated in the same manner to adsorb lithium, and the amount of adsorbed and recovered lithium was measured to be 10 mg / g.
[0033]
【The invention's effect】
As described above, the spinel-type Li ₄ Mn ₅ O ₁₂ composite oxide according to the present invention has a high discharge capacity of 150 mAh / g or more, and is excellent in potential flatness and cycle characteristics. As a positive electrode material for use, and even in the pH range of seawater, the Li adsorption amount is as large as 30 mg / g adsorbent, and can be sufficiently used as a precursor for Li adsorbent.
Moreover, according to the manufacturing method concerning this invention, the said spinel type lithium manganese complex oxide with few crystal defects can be easily manufactured by the self-reactivity which is excellent in uniform reactivity and can be synthesized at low temperature.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a dry powder obtained by an example of the present invention.
FIG. 2 is a graph showing the results of charge / discharge capacity of the secondary battery test of the present invention.
FIG. 3 is a graph showing a result of charge / discharge capacity of a secondary battery test of a comparative example.

Claims (3)

Lithium nitrate and Mn nitrate are mixed stoichiometrically to produce Li ₄ Mn ₅ O _12, and a nonionic water-soluble polymer containing no metal ions is used as a cation support. A method for producing a spinel-type lithium-manganese composite oxide having a composition formula: Li ₄ Mn ₅ O ₁₂ having a lattice constant of 8.160 to 8.130 Å, characterized by adding and mixing, and then removing water by heating. After removing water by heating, further 400 ℃ or more Li ₄ Mn ₅ O ₁₂ 2. The method for producing a spinel type lithium manganese composite oxide according to claim 1, wherein re-heat treatment is performed in a temperature range lower than the decomposition temperature of the composite oxide. The method for producing a spinel-type lithium manganese composite oxide according to claim 1 or 2, wherein the water is removed by heating in a temperature range of 100 to 200 ° C.

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