JP2009091192A - Lithium-cobalt oxide and its preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide highly homogeneous lithium-cobalt oxide by a heat-treatment carried out at a relatively low temperature for a short time, and its preparation method. <P>SOLUTION: A lithium-cobalt oxide powder is prepared by thermally decomposing a lithium-cobalt organic acid salt comprising a trivalent cobalt ion using a preparation method of the lithium-cobalt oxide powder comprising: (1) a step of mixing lithium hydroxide with a cobalt organic acid salt dissolved in an oxidizing medium and; (2) a step of thermally decomposing a precipitated lithium-cobalt organic acid salt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lithium cobalt oxide and a method for producing the same, and particularly relates to a material suitable as a positive electrode active material for a lithium secondary battery.

In recent years, with the spread of small and lightweight mobile information terminals such as cordless and portable AV devices and notebook personal computers, there is a demand for small, lightweight, and high energy density batteries as power sources for driving them. It is getting stronger. In particular, since the lithium secondary battery is a battery having a high energy density, it is expected as a next-generation main battery and has a large potential market scale. Lithium cobalt oxide (LiCoO ₂ ) is mainly used as a positive electrode active material for lithium secondary batteries currently on the market. Lithium cobalt oxide has advantages such as high potential, excellent electrical conductivity, and relatively stable insertion and removal of lithium ions.

  Conventionally, lithium cobalt oxide is obtained by a dry solid phase method in which an oxide raw material powder containing cobalt and a lithium compound powder are mixed and fired. However, in this method, the reactivity of the cobalt oxide powder at the time of solid phase thermal reaction is low, and it is necessary to calcinate for a long time at a high temperature, so that the particles become coarse and then a pulverization treatment is necessary. Furthermore, because the reaction is between solid phases, the raw materials cannot be mixed uniformly at the molecular level, the reaction tends to be non-uniform, and the composition is partially non-uniform during production, resulting in stable quality lithium cobalt. There was a problem that it was difficult to obtain an oxide.

  Furthermore, cobalt oxide and lithium salt are mixed, and the gas atmosphere during firing is controlled in an oxygen atmosphere. However, it is difficult to obtain a uniform composition only by controlling the firing process, and the product It is difficult to fully draw out its original characteristics.

  As a method for solving the above problems, a method of controlling the valence of a transition metal (Co, Ni, etc.) before heat treatment has been attempted. For example, a method in which cobalt oxyhydroxide particles and a lithium salt raw material are mixed and heat-treated (Patent Document 1), a method in which cobalt oxyhydroxide and a lithium compound are reacted using an alcohol as a solvent (Patent Document 2), from a cobalt raw material Disclosed is a method (Patent Document 3) in which divalent cobalt hydroxide produced while adjusting pH is heat-treated at 60 to 200 ° C. with sodium hydroxide and oxygen supply (Patent Document 3). .

All of these methods are methods for increasing the reactivity of the cobalt compound and the lithium compound, but the cobalt compound is dried and mixed with the lithium compound. Once the solvent is removed, the aggregation of the cobalt compound particles is avoided. It is difficult to achieve a uniform mixed state at the atomic level even when mixed with a lithium compound.
JP-A-10-279315 JP 10-310430 A JP 2005-162574 A

  In view of the above, the present invention provides a lithium cobalt oxide having high homogeneity, particularly useful as a positive electrode active material of a lithium secondary battery, and a method for producing the same, by heat treatment at a relatively low temperature for a short time. It is in.

  The present invention for solving the above problems is a method for producing lithium cobalt oxide, which is obtained by thermally decomposing an organic acid salt containing at least trivalent cobalt ions and lithium.

  Further, the present invention includes (1) a step of mixing lithium hydroxide with a cobalt organic acid salt dissolved in an oxidizing medium, and (2) a step of thermally decomposing a deposited precursor. It is a manufacturing method of an oxide.

  Further, the present invention is characterized in that in the above-described method for producing lithium cobalt oxide, the blending molar ratio of lithium to cobalt (Li / Co) is in the range of 1.00 to 1.20.

  The present invention is the above-described method for producing lithium cobalt oxide, wherein the oxidizing agent of the oxidizing medium is at least one of hydrogen peroxide or dissolved oxygen.

  Further, the present invention is characterized in that, in the above-described method for producing lithium cobalt oxide, the cobalt organic acid salt is acetate.

  The lithium cobalt oxide obtained from the present invention is useful as a positive electrode active material for a lithium secondary battery. Moreover, according to this manufacturing method, it is possible to provide a lithium cobalt oxide powder that has high homogeneity and does not require a pulverization treatment, by heat treatment at a relatively low temperature for a short time.

  Embodiments of the present invention are as follows. That is, the lithium cobalt oxide of the present invention can be obtained by thermally decomposing an organic acid salt containing at least trivalent cobalt ions and lithium.

  The organic acid salt containing trivalent cobalt ions and lithium of the present invention is a suitable precursor mixture in which a higher-order cobalt source and a lithium source are present in the vicinity of both at the atomic level. It becomes possible to produce lithium cobalt oxide at a relatively low temperature and in a short time.

  Furthermore, the lithium cobalt oxide of the present invention is manufactured by (1) a step of mixing lithium hydroxide with a cobalt organic acid salt dissolved in an oxidizing medium, and (2) a method of thermally decomposing the deposited precursor. Is obtained.

  In the manufacturing method, the valence of cobalt can be promoted from divalent to trivalent by adding an oxidizing agent to an aqueous solution in which the raw material of the cobalt organic acid salt is dissolved, and allowing the aqueous solution to react in an oxidized state. In order to add and react lithium hydroxide or an aqueous solution in which lithium hydroxide is dissolved in the solution, a precursor mixture of the above-described organic acid salt containing trivalent cobalt ions and lithium can be prepared.

Further, when the precursor mixture particles prepared by the above production method are measured by X-ray diffraction, a diffraction peak is obtained although it cannot be identified. Therefore, the precursor particles may be a crystal or a mixture of crystals. I can confirm. A crystalline lithium cobalt oxide can be produced by subjecting this precursor to a relatively low-temperature baking treatment at 500 to 700 ° C. The obtained lithium cobalt oxide has primary particles that are not fused, and has a uniform particle size. For example, when used as a positive electrode active material for a lithium ion secondary battery, a pulverization treatment is performed. There is no need.

  Another method of adding an oxidizing agent, for example, when adding to an aqueous solution in which lithium hydroxide is dissolved before adding the cobalt organic salt, or adding to an aqueous solution in which lithium hydroxide and cobalt organic salt are dissolved , A reaction between a divalent cobalt organic salt and lithium hydroxide occurs rapidly, and a compound having a large proportion of divalent cobalt, particularly divalent cobalt hydroxide, is produced. When this precursor compound is heat-treated, the heat treatment time becomes longer and the particle size varies as compared with the production method of the present invention.

  Precipitation of the lithium cobalt precursor compound prepared in the present invention is carried out by uniformly mixing a cobalt organic acid salt aqueous solution and a lithium hydroxide powder or a lithium hydroxide aqueous solution, but in order to ensure a uniform reaction, stirring is performed. It is desirable to do it. The method for stirring is not particularly limited, and may be a known method for stirring a normal solution. The reaction temperature is usually preferably room temperature. Room temperature is approximately 10 to 35 ° C. The reaction time is 30 minutes to 10 hours, preferably 1 hour to 5 hours.

  The lithium compound used as the lithium supply source uses lithium hydroxide, which may be a hydrate or an anhydride.

  The mixing ratio of the lithium compound and the cobalt compound is preferably in the range of 1.00 to 1.20 in terms of the molar ratio of Li / Co. More preferably, it is 1.00-1.10. If it is smaller than 1.00, cobalt oxide that does not act as a positive electrode active material other than lithium cobalt oxide remains, and it is difficult to remove this oxide. In this case, the performance of the battery characteristics is degraded. On the other hand, when it becomes larger than 1.20, a lump in which particles generated after heat treatment are strongly aggregated is formed, and when the positive electrode is formed by removing excess lithium by pulverization, the performance of battery characteristics is similarly lowered. You can only get things.

  In the present invention, an oxidizing agent is added to impart oxidizability to the solution. In the production method, cobalt is made into a desired valence, and the lithium cobalt oxide is produced without heating and baking at a high temperature. It is desirable to use an oxidizing agent that can be used, but specifically, hydrogen peroxide or oxygen is preferable because there are no impurities mixed in after the reaction. Hydrogen peroxide and oxygen gas may be used alone or in combination.

In the case of using hydrogen peroxide solution, those having a concentration of 5% to 50% of H ₂ O ₂ are commercially available, and may be appropriate ones such as these. Since it is a thing, you may use this.

  The amount of the oxidizing agent used can be set as appropriate, but when hydrogen peroxide is used, the molar amount may be larger than that of the cobalt source. When oxygen is used, it may be handled by so-called bubbling, which is caused to flow into the cobalt organic acid salt aqueous solution at a predetermined flow rate.

  The cobalt organic acid salt that is the source of cobalt uses acetate. Unlike the case of sulfates and chlorides, for example, even in heat treatment at 500 ° C. or lower, the acetic acid content is effective because it decomposes and no impurities remain. The cobalt acetate may be a hydrate or an anhydride.

  Precipitation of a precursor compound of lithium cobalt is generated by mixing and reacting an aqueous cobalt acetate solution to which an oxidizing agent has been added and lithium hydroxide or an aqueous lithium hydroxide solution. Crystallized particles can be obtained by heating the precursor particles recovered by solid-liquid separation in the air or in an oxygen-containing atmosphere.

  The heating temperature of the precursor compound of lithium cobalt is 400 ° C. to 800 ° C., preferably 500 ° C. to 700 ° C., and the heating time is 30 minutes to 10 hours.

  The lithium cobalt oxide of this invention obtained by the said heat processing can be used conveniently as a positive electrode material of a lithium ion secondary battery. Other than the powder of the present invention used as the positive electrode active material, a lithium ion secondary battery can be produced by employing known constituent materials of a lithium ion secondary battery.

  In general, when lithium cobalt oxide is used as an active material of a lithium ion secondary battery, in order to improve battery characteristics, in some cases, other metals are partially doped. If an acid salt, particularly a metal acetate is used as a raw material, it can be mixed with a cobalt organic acid salt and dissolved in water. If this mixed aqueous solution and lithium hydroxide or lithium hydroxide aqueous solution are mixed and reacted, and the resulting precursor powder is heat-treated, a lithium cobalt oxide doped with a metal other than lithium and cobalt can be obtained. As a raw material to be doped, for example, magnesium acetate, calcium acetate, manganese acetate, nickel acetate, zinc acetate, strontium acetate, barium acetate, lanthanum acetate and hydrates thereof can be used.

(Example 1)
Under stirring, an aqueous solution containing 10 g of cobalt acetate tetrahydrate is gradually added with 10 times the molar amount of hydrogen peroxide solution of cobalt to obtain a solution that changes from reddish purple to yellowish brown containing trivalent cobalt. It was. To this solution, an aqueous solution in which lithium hydroxide monohydrate (Li / Co = 1.05 molar ratio) was dissolved was added and reacted to obtain a precipitate. At this time, the solution turned green. The solvent was evaporated from the precipitate to obtain a precursor powder. The X-ray diffraction pattern of this precursor powder is shown in FIG. Since a sharp diffraction peak was obtained, this precursor powder is an organic acid salt containing cobalt and lithium. In addition, this powder was quantified by ICP emission analysis per unit weight, and after cobalt was reduced using sodium oxalate, oxidation and reduction titration of sulfuric acid KMnO ₄ with excess sodium oxalate was performed to oxidize cobalt. The number was calculated as 2.8. Normally, divalent and trivalent compounds are known for cobalt, and it is clear that cobalt in the organic acid salt containing cobalt and lithium contains trivalent. This powder was fired at 550 ° C. for 1 hour to obtain an active material. When the obtained powder was measured by X-ray diffraction, a diffraction pattern as shown in FIG. 2 was obtained, and it was confirmed that this powder was lithium cobaltate. FIG. 3 shows a scanning electron micrograph of the particle surface. From FIG. 3, it was confirmed that the obtained particles were composed of primary particles having a relatively uniform diameter of about 0.1 to 0.3 μm and that their surfaces were gently necked.

(Example 2)
Lithium cobaltate was obtained in the same manner as in Example 1 except that the Li / Co ratio was changed to 1.10 molar ratio. When the cobalt oxidation number of the precursor powder was calculated in the same manner as in Example 1, it was 2.9.

(Comparative Example 1)
A precipitate was obtained by reacting in the same manner as in Example 1 except that the oxidizing agent was not used. At this time, the solution was reddish purple. The solvent was evaporated from the precipitate to obtain a precursor powder. About this precursor powder, the cobalt oxidation number was analyzed similarly to Example 1, and the value of 2.0 was obtained. This powder was fired at 550 ° C. for 1 hour to obtain an active material. The obtained powder was analyzed by X-ray diffraction and confirmed to be a mixture of lithium cobaltate and tricobalt tetroxide. A scanning electron micrograph of the particle surface is shown in FIG. It was confirmed to be composed of massive primary particles having a diameter of about 0.3 to 1 μm, and the primary particles were fused together to form secondary particles.

(Comparative Example 2)
10 g of cobalt (II) acetylacetonate was dissolved in ethanol, and a solution obtained by dissolving lithium acetate dihydrate (Li / Co = 1.05 molar ratio) in ethanol was added dropwise to this solution with stirring. From this mixed solution, the solvent was removed using an evaporator to obtain a precursor powder. About this precursor powder, the cobalt oxidation number was analyzed similarly to Example 1, and the value of 2.9 was obtained. This powder was fired at 550 ° C. for 1 hour to obtain an active material. When the obtained powder was measured by X-ray diffraction, it was confirmed that this powder was lithium cobaltate. When this powder was observed by SEM, a secondary aggregate in which primary particles were firmly fused was formed. When this powder is used as the positive electrode active material, a pulverization process is required, and when the pulverization process is performed, only powders with varying particle sizes can be obtained.

  Next, using the positive electrode active material obtained as described above, 100 parts by weight of the active material, 3 parts by weight of acetylene black as a conductive material, and 5 parts by weight of polyvinylidene fluoride as a binder are mixed to form a positive electrode mixture. A battery cell was manufactured using metallic lithium for the negative electrode. Using this cell, the charge / discharge characteristics were examined when the battery voltage was 2.0 to 4.0 V. The results are shown in Table 1.

  From these results, it was found that the lithium cobalt oxide obtained in Examples 1 and 2 showed a larger value than that of the comparative example and had excellent battery characteristics. Since the precursor powder according to the present invention contains trivalent cobalt ions, it is not necessary to increase the valence of cobalt at the time of heat treatment, and lithium cobalt oxide can be obtained quickly, and in the precursor lithium cobalt organic acid salt Since cobalt and lithium are uniformly arranged, it is considered that the uniformity of the reaction has increased. Therefore, according to the present invention, it is considered that the primary particles are not fused, and lithium cobalt oxide having a uniform particle size is obtained, and the battery characteristics are improved as compared with the comparative example.

The figure which shows the X-ray-diffraction peak pattern of the precursor compound powder obtained in Example 1 The figure which shows the X-ray-diffraction peak pattern of the powder after baking at 550 degreeC obtained in Example 1 Scanning electron micrograph of the powder after baking at 550 ° C. obtained in Example 1 Scanning electron micrograph of the powder after firing at 550 ° C. obtained in Comparative Example 1

Claims (6)

  A method for producing lithium cobalt oxide, comprising a step of thermally decomposing an organic acid salt containing at least trivalent cobalt ions and lithium into lithium cobalt oxide.   Mixing lithium hydroxide with cobalt organic acid salt dissolved in an oxidizing medium to obtain a precursor containing at least trivalent cobalt ions, and thermally decomposing the precursor to form lithium cobalt oxide A method for producing lithium cobalt oxide.   3. The method for producing lithium cobalt oxide according to claim 1, wherein a blending molar ratio of lithium to cobalt in the lithium cobalt oxide is in a range of 1.00 to 1.20.   3. The method for producing a lithium cobalt oxide according to claim 2, wherein the oxidizing agent in the oxidizing medium is at least one of hydrogen peroxide or dissolved oxygen.   The method for producing a lithium cobalt oxide according to claim 2, wherein the cobalt organic acid salt is an acetate salt.   The lithium cobalt oxide manufactured by the manufacturing method of the lithium cobalt oxide in any one of Claims 1 thru | or 5.