JP7125227B2 - Method for producing lithium-containing cobalt oxide having spinel crystal phase - Google Patents

Description

The present application discloses a method for producing a lithium-containing cobalt oxide having a spinel-type crystal phase, and the like.

As disclosed in Patent Document 1 and Non-Patent Documents 1 to 5, lithium-containing metal oxides having a spinel crystal phase are known. In particular, a lithium-containing cobalt oxide having a spinel crystal phase as disclosed in Non-Patent Document 1 is expected as a new positive electrode active material for lithium ion batteries.

JP-A-6-203834

Eungje Lee et al., ACS Appl. Mater. Interfaces, 8, 27720-27729 (2016) S. Choi et al., Journal of The Electrochemical Society, 149(2), A162-A166 (2002) Hong-Yang Lu et al., Applied Surface Science, 177, 103-113 (2001) Wen-jie Peng et al., Journal of Power Sources, 153, 174-176 (2006) S. Choi et al., Journal of Solid State Chemistry, 164, 332-338 (2002)

As disclosed in Patent Document 1, Non-Patent Documents 3 and 4, etc., the composite oxide of lithium and a transition metal other than cobalt has a spinel-type crystal phase that is thermally stable. A lithium-containing transition metal oxide having a spinel crystal phase can be produced in a short period of time. On the other hand, as for the composite oxide of lithium and cobalt, since the layered rock salt type crystal phase is more thermally stable than the spinel type crystal phase, it is difficult to sinter at a high temperature to obtain the spinel type crystal phase. be. For example, in Non-Patent Document 1, in producing a lithium-containing cobalt oxide having a spinel-type crystal phase, firing is performed at 400° C. to 500° C. for 6 days by a solid-phase method. Thus, the lithium-containing cobalt oxide having a spinel-type crystal phase has the problem that it takes a long time to produce.

As one means for solving the above problems, the present application provides a step of dissolving a metal acetate in a protic polar solvent to obtain a mixed solution, a step of evaporating the mixed solution to dryness to obtain a precursor, and calcining the precursor.

“Having a spinel-type crystal phase” means that at least a diffraction peak derived from a spinel-type crystal phase is confirmed in X-ray diffraction.

According to the production method of the present disclosure, a homogeneous and particulate precursor is obtained by an evaporation to dryness method using a metal acetate and a solvent, and the precursor is calcined to obtain lithium having a spinel crystal phase. The containing cobalt oxide can be produced in a short time.

It is a figure for demonstrating an example of the flow of the manufacturing method of this indication. 1 is a diagram showing X-ray diffraction peaks of lithium cobaltate according to Example 1 and Comparative Example 1. FIG. 2 is a diagram showing charge/discharge curves (4.2V-2.5V) of lithium ion batteries using lithium cobaltate according to Example 1 and Comparative Example 1. FIG.

1. Method for Producing Lithium-Containing Cobalt Oxide Having Spinel Crystalline Phase FIG. 1 shows an example of the production method of the present disclosure. The production method S10 shown in FIG. 1 comprises a step S1 of dissolving a metal acetate in a protic polar solvent to obtain a mixed solution, a step S2 of evaporating the mixed solution to dryness to obtain a precursor, and calcining the precursor. and step S3. Through steps S1 to S3, a lithium-containing cobalt oxide having a spinel crystal phase can be produced in a short time.

1.1. process S1
In step S1, a metal acetate is dissolved in a protic polar solvent to obtain a mixed solution. Metal acetates contain at least a lithium source and a cobalt source. Specifically, it preferably contains lithium acetate and cobalt acetate. The metal acetate may contain metal acetates other than lithium acetate and cobalt acetate as long as the above problems can be solved. For example, when a transition metal other than cobalt is doped, an acetate of the transition metal other than cobalt may be included. The mixing ratio of each metal acetate may be appropriately adjusted according to the desired composition. For example, the finally obtained lithium-containing cobalt oxide is Li _x My Co _z O _2±δ ( _M is a transition metal other than Co, 0.8≦x≦1.2, 0≦y≦0 .15, 0.8≦z≦1.2, and 0.8≦y+z≦1.2). In the lithium-containing cobalt oxide, the molar ratio of the transition metal to Li is preferably 1 (that is, (y + z) / x = 1), but even if the amount of Li is slightly excessive relative to the transition metal, Alternatively, even if Li is somewhat deficient, it is possible to generate a spinel crystal phase. In this respect, for example, as shown in the above composition formula, 0.8≤x≤1.2, 0≤y≤0.15, 0.8≤z≤1.2, 0.8≤y+z≤1. 2 is preferred. In particular, it is more preferable that the molar ratio ((y+z)/x) of the transition metal to Li is 0.8 or more and 1.2 or less. The lower limit of the molar ratio ((y+z)/x) is preferably 0.9 or more, more preferably 0.95 or more, and the upper limit is more preferably 1.1 or less, still more preferably 1.05 or less. In the lithium-containing cobalt oxide, the molar ratio of O to Li (O/Li) is preferably 2. It is possible to form a spinel-type crystal phase even if the In this regard, it is preferable that the molar ratio of O to Li (O/Li) is, for example, 1.8 or more and 2.2 or less. Alternatively, in the above composition formula, δ is preferably 0.2 or less. The protic polar solvent may be any solvent capable of dissolving the above metal acetate. Examples include water and alcohol. Water is particularly preferred. The mixing ratio of the metal acetate and the protic polar solvent in the mixed solution is not particularly limited.

1.2. process S2
In step S2, the mixed solution obtained in step S1 is evaporated to dryness to obtain a precursor. Evaporation of the mixed solution to dryness may be carried out using a general heating means. The temperature for evaporation to dryness may be any temperature at which the solvent can be evaporated. Depending on the type of protic polar solvent, the temperature can be, for example, 80° C. or higher and 280° C. or lower. The time for evaporation to dryness is not particularly limited, and may be any time that can sufficiently remove the solvent. The atmosphere for evaporation to dryness is not particularly limited either. For example, it can be an air atmosphere. The pressure is also not particularly limited. A reduced pressure may be applied to shorten the time to evaporate to dryness. It can be said that the precursor obtained in step S2 is a homogeneous mixture of lithium, cobalt, etc. at the atomic level, unlike the powder mixture obtained by the solid-phase method. In addition, it can be said that it is in the form of finer particles and has a larger specific surface area than the powder mixture obtained by the solid-phase method.

1.3. Step S3
In step S3, the precursor obtained in step S2 is fired. Since the layered rock salt type crystal phase is generally more stable to heat than the spinel type crystal phase, if the firing temperature in step S3 is too high, the layered rock salt type crystal phase is generated rather than the spinel type crystal phase. put away. That is, in order to obtain the desired spinel crystal phase in the above precursor, it is preferable to set the firing temperature in step S3 to a low temperature. In particular, according to the findings of the present inventor, the spinel-type crystal phase is easily obtained by setting the firing temperature in step S3 to 200° C. or higher and 550° C. or lower. The lower limit of the calcination temperature is more preferably 250° C., more preferably 280° C. or higher, and the upper limit is more preferably 430° C. or lower, still more preferably 410° C. or lower. The firing time in step S3 may be adjusted according to the firing temperature. Since the manufacturing method S10 employs the evaporation-to-dryness method, the baking time can be shortened as compared with the conventional solid-phase method. For example, it is preferable to set the firing time to 120 hours or less. The firing atmosphere in step S3 may be any atmosphere capable of producing lithium-containing cobalt oxide. For example, an air atmosphere, an oxygen atmosphere, or the like can be used. The pressure in step S3 is not particularly limited.

As described above, according to the manufacturing method S10, a uniform and fine particle precursor is obtained by an evaporation to dryness method using a metal acetate and a solvent, and the precursor is calcined to form a spinel crystal phase. It is possible to produce lithium-containing cobalt oxide having a short time.

1.4. Others The lithium-containing cobalt oxide produced by the production method S10 has a spinel-type crystal phase with high crystallinity. For example, in X-ray diffraction measurement using CuKα as a radiation source, it is possible to set the half width of the diffraction peak corresponding to the (044) plane to 1 degree or less. By increasing the crystallinity of the spinel-type crystal phase, for example, when it is applied as a positive electrode active material for a lithium-ion battery, the resistance is reduced, and an improvement in the capacity of the battery can be expected.

In the lithium-containing cobalt oxide produced by production method S10, at least a diffraction peak derived from the spinel crystal phase is confirmed in X-ray diffraction. Here, the lithium-containing cobalt oxide produced by the production method S10 may contain a small amount of a different phase other than the spinel-type crystal phase within a range in which the desired performance can be exhibited. Depending on the synthesis conditions such as the firing temperature, for example, the spinel-type crystal phase and the layered rock salt-type crystal phase may be included. However, from the viewpoint of improving the capacity when used as a positive electrode active material for a battery, the lithium-containing cobalt oxide produced by the production method S10 has only a diffraction peak derived from the spinel crystal phase in X-ray diffraction. preferably.

2. Applications As described above, the lithium-containing cobalt oxide produced by the production method of the present disclosure can be suitably used as a positive electrode active material for lithium ion batteries. That is, the technology of the present disclosure also has an aspect as a lithium ion battery. A lithium-ion battery of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte, and the positive electrode includes the lithium-containing cobalt oxide of the present disclosure as a positive electrode active material.

2.1. Positive Electrode The positive electrode may have the same configuration as the conventional one, except that it includes the positive electrode active material of the present disclosure. For example, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer containing the positive electrode active material of the present disclosure above. The positive electrode current collector may be made of, for example, various metals. The positive electrode active material layer may optionally contain a binder and a conductive aid in addition to the positive electrode active material. The positive electrode active material of the present disclosure has a small expansion/shrinkage rate of the active material during charging and discharging, and is particularly advantageous in a solid battery in which interfacial contact between particles is important. In this regard, when a solid battery is employed as the lithium ion battery, it is preferable that the positive electrode active material layer contains a solid electrolyte. As the solid electrolyte, an inorganic solid electrolyte such as an oxide solid electrolyte or a sulfide solid electrolyte is preferable, and a sulfide solid electrolyte is more preferable. When a sulfide solid electrolyte is included in the positive electrode, a coating layer such as a lithium niobate layer is provided on the surface of the positive electrode active material from the viewpoint of suppressing the formation of a high resistance layer at the interface between the positive electrode active material and the sulfide solid electrolyte. may be provided. Since the configuration other than the positive electrode active material is self-evident from common technical knowledge, further explanation is omitted.

2.2. Negative Electrode As the negative electrode, a known negative electrode for lithium-ion batteries can be employed. For example, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material. The negative electrode current collector may be made of, for example, various metals. As the negative electrode active material, a material having a lithium ion charge/discharge potential that is more base than the positive electrode active material of the present disclosure may be adopted. The negative electrode active material layer may optionally contain a binder and a conductive aid in addition to the negative electrode active material. Moreover, when a solid battery is employed as the lithium ion battery, the negative electrode active material layer preferably contains the solid electrolyte described above. Since the structure of the negative electrode is self-evident from common technical knowledge, further explanation is omitted.

2.3. Electrolyte The electrolyte is for conducting lithium ions between the positive and negative electrodes described above. Either an electrolytic solution or a solid electrolyte may be used as the electrolyte. When an electrolytic solution is employed, a separator may be arranged between the positive electrode and the negative electrode and impregnated with the electrolytic solution. On the other hand, when using a solid electrolyte, a solid electrolyte layer may be arranged between the positive electrode and the negative electrode. The solid electrolyte layer contains the solid electrolyte described above and optionally a binder. Since the structure of the electrolyte is self-evident from common technical knowledge, further explanation is omitted.

2.4. Other Configurations A lithium-ion battery may include the positive electrode, the negative electrode, and the electrolyte described above, and may also include terminals, a battery case, and the like, if necessary. Since these configurations are self-evident from common technical knowledge, further explanation is omitted.

As described above, the lithium ion battery of the present disclosure employs the positive electrode active material of the present disclosure in the positive electrode, and the positive electrode active material has high crystallinity. Therefore, the resistance in the positive electrode can be reduced, and the capacity and the like can be improved. The lithium ion battery of the present disclosure is suitably used not only as a primary battery but also as a secondary battery.

1. Synthesis of Lithium-Containing Cobalt Oxide Having Spinel Crystalline Phase (Example 1)
As metal acetates, lithium acetate and cobalt acetate were weighed so that the molar ratio was 1:1, and dissolved in deionized water, which is a protic polar solvent, to obtain a mixed solution. While stirring the obtained mixed solution with a stirrer, it was heated to 250° C. on a hot plate and evaporated to dryness to obtain a precursor. A lithium-containing cobalt oxide was synthesized by baking the obtained precursor at 300° C. for 120 hours in an air atmosphere.

(Example 2)
A lithium-containing cobalt oxide was synthesized in the same manner as in Example 1, except that the firing temperature was 400° C. and the firing time was 2 hours.

(Comparative example 1)
Cobalt oxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) are mixed in a stoichiometric ratio, pelletized, fired at 300° C. for 120 hours in an air atmosphere, and then ball milled (BM). was performed at 590 rpm for 8 hours. A lithium-containing cobalt oxide was obtained by performing pelletization, firing and BM treatment five times.

2. Confirmation of Crystal Phase The lithium-containing cobalt oxides according to Examples 1 and 2 and Comparative Example 1 were subjected to X-ray diffraction measurement using CuKα as a radiation source, and diffraction peaks were confirmed. Diffraction peaks derived from the spinel-type crystal phase were confirmed for all of them.

3. Preparation of Evaluation Cell In order to evaluate the performance of the lithium-containing cobalt oxides according to Examples 1 and 2 and Comparative Example 1 as positive electrode active materials, evaluation cells were prepared. Specifically, they were weighed so that the mass ratio of lithium-containing cobalt oxide:conductive material:binder=85:10:5 was added and mixed into NMP to prepare a slurry. The obtained slurry was applied on an Al foil and dried overnight at 120° C. to obtain a positive electrode. Using the obtained positive electrode, separator, negative electrode (Li foil), and F-substituted carbonate-based electrolytic solution, a CR2032 coin cell was produced.

4. Charge/Discharge Test The prepared coin cell was charged and discharged under the following conditions, and the discharge capacity was confirmed.
CC charging: current 0.1C, termination condition 4.5V
CC discharge: current 0.1C, termination condition 2.5V

5. Evaluation Results Table 1 below shows the evaluation results of X-ray diffraction and charge/discharge tests. 2 shows the X-ray diffraction peaks of the lithium-containing cobalt oxides according to Example 1 and Comparative Example 1. As shown in FIG. Furthermore, FIG. 3 shows charge-discharge curves (4.2V-2.5V) of coin cells using the lithium-containing cobalt oxides according to Example 1 and Comparative Example 1. As shown in FIG.

As is clear from the results shown in Table 1 and FIG. 2, Examples 1 and 2 had sharper diffraction peaks than Comparative Example 1, indicating that the crystallinity of the spinel crystal phase was high. For example, the half width of the diffraction peak corresponding to the (044) plane near 65° was smaller in Examples 1 and 2 than in Comparative Example 1 by 0.26°. In Examples 1 and 2 using the evaporation-to-drying method, unlike Comparative Example 1 using the solid-phase method, lithium and cobalt are uniformly mixed at the atomic level in the precursor, and the precursor becomes fine particles. Therefore, it is considered that crystallization tends to proceed during firing.

As is clear from the results shown in Table 1 and FIG. 3, Examples 1 and 2 had lower overvoltages and larger capacities than Comparative Example 1. As described above, the crystallinity of Examples 1 and 2 is higher than that of Comparative Example 1, so it is considered that the resistance is reduced.

The lithium-containing composite oxide produced by the production method of the present disclosure can be suitably used as a positive electrode active material for lithium ion batteries. Lithium ion batteries using the positive electrode active material can be widely used, for example, from small power sources for portable devices to large power sources for vehicles.

Claims (1)

a step of dissolving a metal acetate only in a protic polar solvent capable of dissolving the metal acetate to obtain a mixed solution;
obtaining a precursor by evaporating the mixed solution to dryness;
calcining the precursor at a temperature of 200° C. or higher and 550° C. or lower ;
comprising
A method for producing a lithium-containing cobalt oxide having a spinel crystal phase.

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