JP2020021710A - Cathode active material for lithium ion battery - Google Patents

Abstract

To provide, when spinel-type lithium cobaltate is applied as a cathode active material for a lithium ion batteries, the initial coulomb efficiency may be reduced.SOLUTION: A spinel-type lithium cobaltate is doped with aluminum. Specifically, a cathode active material for a lithium ion battery has a spinel-type crystal phase containing lithium, cobalt, aluminum, and oxygen, and has a composition represented by LiCoAlO(0.85≤x<1, 0<y≤0.15, 0.85<x+y≤1.15).SELECTED DRAWING: Figure 6

Description

  The present application discloses a positive electrode active material and the like used for a lithium ion battery.

  As disclosed in Patent Documents 1 to 3, lithium cobaltate having a layered rock salt type crystal phase, lithium manganate having a spinel type crystal phase, and the like are widely used as positive electrode active materials used in lithium ion batteries. . On the other hand, in recent years, lithium cobalt oxide having a spinel-type crystal phase as disclosed in Non-Patent Document 1 has been developed, and is expected as a new positive electrode active material for a lithium ion battery.

JP 2011-001256 A JP-A-2002-289175 JP-A-2006-143539

Eungje Lee et al., ACS Appl. Mater. Interfaces 2016, 8, 27720-27729

  According to the findings of the present inventor, lithium cobalt oxide having a spinel-type crystal phase disclosed in Non-Patent Document 1 has a small change in lattice constant associated with insertion and desorption of lithium ions. It is considered that when applied as a positive electrode active material, the volume change of the positive electrode during charge and discharge can be reduced. However, when a lithium-ion battery is configured using lithium cobaltate having a spinel-type crystal phase as a positive electrode active material, the initial coulomb efficiency of the battery may be reduced.

This application is as a means for solving the above problems, has a spinel type crystal phase containing lithium and cobalt and aluminum and _{oxygen, LiCo x Al y O 2 ±} δ (0.85 ≦ x <1, A positive electrode active material for a lithium ion battery having a composition represented by 0 <y ≦ 0.15, 0.85 <x + y ≦ 1.15) is disclosed.

  According to a new finding of the present inventor, when a specific amount of aluminum is doped in spinel-type lithium cobalt oxide as in the positive electrode active material of the present disclosure, when applied to a lithium ion battery, First coulomb efficiency is greatly increased.

FIG. 2 is a schematic diagram for explaining a configuration of a lithium ion battery 10. FIG. 1 is a schematic diagram for explaining a configuration of a lithium ion battery system 100. FIG. 4 is a diagram for explaining an example of a control flow in the lithium ion battery system 100. It is a figure which shows the X-ray diffraction peak of the positive electrode active material which concerns on Examples 1-5 and Comparative Examples 1-5. FIG. 3 is a diagram showing SEM images of the positive electrode active materials according to Example 1 and Comparative Example 1. FIG. 4 is a diagram showing a first charge / discharge curve (4.45 V-2.5 V) of a lithium ion battery using the positive electrode active material according to Example 1 and Comparative Example 1.

1. The positive electrode active material of the positive electrode active material present disclosure, a cathode active material for use in lithium ion batteries, have a spinel type crystal phase containing lithium and cobalt and aluminum and _{oxygen, LiCo x Al y O 2 ±} δ (0.85 ≦ x <1, 0 <y ≦ 0.15, 0.85 <x + y ≦ 1.15).

1.1. Crystal Phase The positive electrode active material of the present disclosure has a spinel-type crystal phase containing lithium, cobalt, aluminum, and oxygen. “Having a spinel crystal phase” means that at least a diffraction peak derived from the spinel crystal phase is confirmed in X-ray diffraction. For example, in the positive electrode active material of the present disclosure, in X-ray diffraction measurement using CuKα as a source, 2θ = 19.8 ± 0.4 °, 37.3 ± 0.4 °, 39.0 ± 0.4 ° , 45.3 ± 0.4 °, 49.7 ± 0.4 °, 60.1 ± 0.4 °, 66.1 ± 0.4 ° and 69.5 ± 0.4 ° It is preferable that a diffraction peak derived from the crystal phase is confirmed. It is considered that the spinel-type lithium cobalt oxide and the positive electrode active material of the present disclosure have different crystal lattice constants in the spinel-type crystal phase. That is, after confirming the composition of the positive electrode active material by X-ray diffraction or elemental analysis, by confirming the crystal lattice constant of the spinel-type crystal phase by X-ray diffraction, it is possible to obtain “lithium, cobalt, aluminum, oxygen, It is considered that the presence or absence of the “spinel-type crystal phase containing

  In the positive electrode active material of the present disclosure, the spinel-type crystal phase includes lithium, cobalt, aluminum, and oxygen. In other words, the positive electrode active material of the present disclosure can be said to be a material in which some elements of spinel-type lithium cobalt oxide are replaced with aluminum. It is considered that this stabilizes the spinel crystal phase.

  The positive electrode active material of the present disclosure has the specific spinel-type crystal phase described above. On the other hand, the positive electrode active material of the present disclosure may include other crystal phases in addition to the spinel crystal phase as long as the above-described problem can be solved. For example, when synthesizing a composite oxide containing lithium and cobalt, a thermally stable layered rock salt type crystal phase may be formed together with a spinel type crystal phase. The effect of can be exhibited. In this regard, the positive electrode active material of the present disclosure may include a layered rock salt type crystal phase in addition to the spinel type crystal phase. Preferably, in the positive electrode active material of the present disclosure, only a diffraction peak derived from a spinel-type crystal phase is confirmed in the X-ray diffraction measurement.

1.2. Composition The positive electrode active material of the present disclosure has a composition represented by LiCo _x Al _y O _{2 ± δ} (0.85 ≦ x <1, 0 <y ≦ 0.15, 0.85 <x + y ≦ 1.15). Have. According to the findings of the present inventors, the initial coulomb efficiency of the battery is significantly increased when the substitution amount (doping amount) of aluminum in the spinel-type lithium cobalt oxide is in the specific range represented by the above composition formula.

  From the viewpoint of further increasing Coulomb efficiency, x in the above composition formula is more preferably 0.85 ≦ x ≦ 0.975, further preferably 0.85 ≦ x ≦ 0.95, and particularly preferably. 0.85 ≦ x ≦ 0.93. y is more preferably 0.025 ≦ y ≦ 0.15, further preferably 0.05 ≦ y ≦ 0.15, and particularly preferably 0.07 ≦ y ≦ 0.15.

  In the positive electrode active material of the present disclosure, the total molar ratio of Co and Al to Li is preferably 1 (x + y = 1). However, even if Li is somewhat excessive, or Li is slightly insufficient. However, the spinel-type crystal phase can be generated and maintained, and the desired effect can be exhibited. In this regard, the molar ratio of Co and Al to Li should be more than 0.85 and 1.15 or less (0.85 <x + y ≦ 1.15) as shown in the above composition formula. The lower limit is preferably 0.9 or more, more preferably 0.95 or more, and the upper limit is preferably 1.1 or less, more preferably 1.05 or less.

  In the positive electrode active material of the present disclosure, the molar ratio of O to Li (O / Li) is preferably 2 in view of the stoichiometric ratio of spinel-type lithium cobalt oxide. The spinel crystal phase can be generated and maintained even when oxygen is excessive or partially deficient than the ratio, and a desired effect can be exhibited. In this regard, the molar ratio of O to Li (O / Li) is preferably, for example, 1.8 or more and 2.2 or less. Alternatively, in the above composition formula, δ is preferably 0.2 or less.

1.3. Shape The shape and size of the positive electrode active material of the present disclosure are not particularly limited, as long as they are applicable to the positive electrode of a lithium ion battery. It is preferably in the form of particles.

1.4. Effect The positive electrode active material of the present disclosure is obtained by doping a specific amount of aluminum in a spinel-type lithium cobalt oxide, so that the initial coulomb efficiency of the battery when applied to a lithium ion battery, as compared to a case where aluminum is not included. Greatly increase. It is considered that the spinel crystal phase was stabilized by aluminum.

2. Method for Producing Positive Electrode Active Material The positive electrode active material of the present disclosure is, for example, a lithium source, a cobalt source, and a first step of obtaining a mixture by mixing an aluminum source, and heating the mixture to form a spinel-type crystal phase. And a second step of obtaining a composite oxide having the same.

2.1. First Step In the first step, a lithium source, a cobalt source, and an aluminum source are mixed to obtain a mixture. Examples of the lithium source include a lithium compound and lithium metal. Examples of the lithium compound include lithium carbonate, lithium oxide, lithium hydroxide, and lithium acetate. In the case of the solid phase method, lithium carbonate is preferred. In the case of the liquid phase method (evaporation to dryness method), lithium acetate is preferred. Examples of the cobalt source include a cobalt compound and metallic cobalt. Examples of the cobalt compound include cobalt carbonate, cobalt oxide, cobalt hydroxide, and cobalt acetate. In the case of the solid phase method, cobalt oxide is preferred, and Co ₃ O ₄ is more preferred. In the case of the liquid phase method (evaporation to dryness method), cobalt acetate is preferred. Aluminum sources include aluminum compounds and metallic aluminum. Examples of the aluminum compound include aluminum carbonate, aluminum oxide, aluminum hydroxide, and aluminum acetate. In the case of the solid phase method, aluminum oxide is preferred. In the case of the liquid phase method (evaporation to dryness method), aluminum acetate is preferred. In addition, the above various compounds may be hydrates.

  The molar ratio of lithium, cobalt, and aluminum in the mixture may be any ratio that satisfies the above-described composition in the positive electrode active material of the present disclosure.

  The method of mixing the lithium source and the cobalt source is not particularly limited, and various methods such as dry mixing without using a solvent and wet mixing using a solvent can be adopted. In the first step, the raw materials may be dissolved to form a mixture (mixed solution) composed of a solution, or the powders may be mixed to form a powder mixture. Mixing may be performed manually using a mortar or the like, or may be performed mechanically using a ball mill or the like.

  In particular, in the first step, a raw material is dissolved in a solvent to obtain a mixed solution by a liquid phase method (evaporation to dryness method), and then the mixed solution is evaporated to dryness to obtain a solid precursor. Is preferred. Examples of the solvent used in this case include a protic polar solvent such as water and alcohol. The precursor obtained after evaporation to dryness has a state in which lithium, cobalt and aluminum are uniformly mixed at the atomic level, and has a large specific surface area in the form of fine particles. By heating and baking such a precursor in the second step described later, a spinel-type crystal phase can be generated in a short time.

2.2. Second Step In the second step, the mixture obtained in the first step is heated to obtain a composite oxide having a spinel-type crystal phase. Usually, in the composite oxide of lithium and cobalt, the layered rock salt-type crystal phase is more stable to heat than the spinel-type crystal phase. A layered rock salt type crystal phase is generated rather than a phase. That is, when a desired spinel-type crystal phase is obtained from the above mixture, it is preferable that the heating temperature in the second step be low and the heating time be long. In particular, according to the knowledge of the inventor, a desired spinel-type crystal phase is easily obtained by setting the heating temperature in the second step to 250 ° C. or more and 600 ° C. or less. The lower limit of the heating temperature is more preferably 280 ° C, further preferably 300 ° C or higher, and the upper limit is more preferably 550 ° C or lower, further preferably 510 ° C or lower. The heating time in the second step may be adjusted depending on the heating temperature. For example, in the case of the solid phase method, the crystallinity of the spinel type crystal phase can be increased by heating for one week or more. On the other hand, in the case of the liquid phase method (evaporation to dryness method), the crystallinity of the spinel-type crystal phase can be increased even if the heating time is 120 hours or less. The heating atmosphere in the second step may be any atmosphere that can generate a composite oxide. For example, an air atmosphere, an oxygen atmosphere, or the like can be used.

3. Lithium ion battery The technology of the present disclosure also has aspects as a lithium ion battery. FIG. 1 shows an example of the configuration of the lithium ion battery of the present disclosure. The lithium ion battery 10 shown in FIG. 1 includes a positive electrode 1, a negative electrode 2, an electrolyte 3 disposed between the positive electrode 1 and the negative electrode 2, and the positive electrode 1 includes the positive electrode active material of the present disclosure. And

3.1. Positive electrode 1
The positive electrode 1 may have the same configuration as the conventional one, except that the positive electrode 1 includes the positive electrode active material of the present disclosure. For example, the positive electrode 1 includes a positive electrode current collector 1a and a positive electrode active material layer 1b including the positive electrode active material of the present disclosure. The positive electrode current collector 1a may be made of, for example, various metals. The positive electrode active material layer 1b may optionally contain a binder or a conductive additive in addition to the positive electrode active material. The positive electrode active material layer 1b may contain a positive electrode active material other than the positive electrode active material according to the present disclosure, in addition to the positive electrode active material according to the present disclosure, as long as the above-described problem can be solved. For example, a lithium metal composite oxide having a layered rock salt type crystal phase, a lithium metal phosphate compound having an olivine type crystal phase, and the like can be given. The positive electrode active material of the present disclosure is particularly advantageous in a solid battery in which the rate of expansion and contraction of the active material due to charge and discharge is small, and interfacial contact between particles is important. In other words, the lithium ion battery of the present disclosure is preferably an all solid state battery. When employing an all-solid-state battery as the lithium-ion battery, it is preferable that the positive electrode active material layer 1b 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. As the sulfide solid electrolyte, for example, a solid electrolyte containing Li, P, and S as constituent elements can be used. _{Specifically, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Si 2 S-P 2 S 5, LiI-LiBr-Li 2 S-P _{2 S 5, LiI-Li 2} S-P 2 S 5, LiI-Li 2 O-Li 2 S-P 2 S 5, LiI-Li 2 S-P 2 O 5, LiI-Li 3 PO 4 -P 2 _{S 5, Li 2 S-P} 2 S 5 -GeS 2 , and the like. Among them, a sulfide solid electrolyte containing Li ₂ SP ₂ S ₅ is more preferable. Only one solid electrolyte may be used alone, or two or more solid electrolytes may be used in combination. When the sulfide solid electrolyte is contained in the positive electrode 1, the surface of the positive electrode active material is coated with a lithium niobate layer or the like 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. A layer may be provided. Since the configuration other than the positive electrode active material is obvious from common technical knowledge, further description is omitted.

3.2. Negative electrode 2
As the negative electrode 2, a known negative electrode of a lithium ion battery can be adopted. For example, the negative electrode 2 includes a negative electrode current collector 2a and a negative electrode active material layer 2b containing a negative electrode active material. The negative electrode current collector 2a may be made of, for example, various metals. As the negative electrode active material, a material whose lithium ion charge / discharge potential is lower than that of the positive electrode active material of the present disclosure may be used. The negative electrode active material layer 2b may optionally contain a binder or a conductive assistant in addition to the negative electrode active material. When a solid-state battery is used as the lithium-ion battery, the negative electrode active material layer 2b preferably contains the above-described solid electrolyte. Since the configuration of the negative electrode is obvious from common technical knowledge, further description will be omitted.

3.3. Electrolyte layer 3
The electrolyte layer 3 is for conducting lithium ions between the positive electrode 1 and the negative electrode 2 described above. In the electrolyte layer 3, any of an electrolytic solution and a solid electrolyte may be adopted. When an electrolytic solution is employed, a separator may be disposed between the positive electrode and the negative electrode, and the separator may be impregnated with the electrolytic solution. On the other hand, when a solid electrolyte is employed, a solid electrolyte layer may be provided between the positive electrode and the negative electrode. The solid electrolyte layer contains the solid electrolyte described above and optionally a binder. As described above, the positive electrode active material of the present disclosure is particularly advantageous in a solid-state battery in which the rate of expansion and contraction of the active material due to charge and discharge is small, and interfacial contact between particles is important. In this regard, the electrolyte layer 3 is preferably a solid electrolyte layer containing an inorganic solid electrolyte such as an oxide solid electrolyte or a sulfide solid electrolyte, and more preferably a layer containing a sulfide solid electrolyte. Since the configuration of the electrolyte layer 3 is obvious from common technical knowledge, further description is omitted.

3.4. Other Configurations The lithium ion battery 10 may include the positive electrode 1, the negative electrode 2, and the electrolyte layer 3 described above, and may further include a terminal, a battery case, and the like as necessary. Since these configurations are obvious from the common technical knowledge, further description is omitted.

3.5. Effects In the lithium ion battery of the present disclosure, the positive electrode active material of the present disclosure is employed in the positive electrode, the initial coulomb efficiency is high, and the volume change of the positive electrode during charge and discharge is small. The lithium ion battery of the present disclosure is suitably used not only as a primary battery but also as a secondary battery.

4. Lithium-ion battery system The positive electrode active material of the present disclosure is more excellent in stability of the spinel-type crystal phase than the conventional positive electrode active material, and can function as, for example, a high-voltage active material. In this regard, when charging / discharging a lithium ion battery including the positive electrode active material of the present disclosure, the charge / discharge control unit controls the charging / discharging of the lithium ion battery to increase the discharge start voltage or the charge cutoff voltage to a high voltage. It is preferable that

FIG. 2 schematically shows a configuration example of the lithium-ion battery system 100. FIG. 3 shows an example of a control flow in the lithium ion battery system 100. As shown in FIGS. 2 and 3, the lithium-ion battery system 100 includes a lithium-ion battery 10 including the above-described positive electrode active material of the present disclosure and a charge / discharge control unit 20 that controls charging and discharging of the lithium-ion battery 10. provided, the charge and discharge control unit 20, a start potential or charge cutoff potential of the discharge of the positive electrode of the lithium ion battery 10 4.0V (vs.Li ⁺ / Li) or more, preferably 4.2V (vs.Li ⁺ / Li) or more, more preferably 4.3 V (vs. Li ⁺ / Li) or more.

  The charge / discharge control unit 20 only needs to be able to control the charge and discharge of the lithium ion battery 10 as described above. For example, when charging the lithium ion battery 10 using a power supply, the potential of the positive electrode of the lithium ion battery 1 is sequentially measured, and when the measured potential of the positive electrode is less than a predetermined voltage, the charging is continued, If the potential is equal to or higher than a predetermined voltage, the supply of electricity from the power supply may be stopped to stop charging.

  The same applies to the discharge starting potential. That is, when performing the first discharge after charging the lithium ion battery 10, the potential of the positive electrode is measured before performing the first discharge, and when the measured potential of the positive electrode is less than the predetermined voltage, The lithium ion battery 10 may be charged without discharging the battery 10, and the first discharge may be performed when the potential of the positive electrode becomes equal to or higher than a predetermined voltage due to the charging of the lithium ion battery 10.

When charging and discharging of the lithium ion battery 10 is controlled by the charge / discharge control unit 20, the upper limit of the discharge start potential or the charge cutoff potential of the lithium ion battery 10 is not particularly limited, but the potential is set too high. The effect is small even at a high potential. Rather, there is a concern that the battery material may deteriorate or decompose. In this regard, the charge / discharge control unit 20 preferably sets the discharge start potential or charge cutoff potential of the positive electrode of the lithium ion battery 10 to 5.3 V (vs. Li ⁺ / Li) or less. More preferably, the voltage is set to 5.1 V (vs. Li ⁺ / Li) or less, and still more preferably 5.0 V (vs. Li ⁺ / Li) or less.

1. Synthesis of positive electrode active material (spinel-type composite oxide) (Example 1)
Lithium acetate as a lithium source, cobalt acetate as a cobalt source, and aluminum acetate as an aluminum source were dissolved in ion-exchanged water as a protic polar solvent to obtain a mixed solution. The obtained mixed solution was heated to 250 ° C. on a hot plate while being stirred with a stirrer, and evaporated to dryness to obtain a solid precursor. The obtained precursor was calcined at 400 ° C. for 2 hours in an air atmosphere to obtain a positive electrode active material (LiCo _0.9 Al _0.1 O _{2 ± δ} ) according to Example 1.

(Example 2)
A positive electrode active material (LiCo _0.9 Cr _0.1 O _{2 ± δ} ) according to Example 2 was obtained in the same manner as in Example 1 except that the firing temperature of the precursor was 450 ° C.

(Example 3)
A positive electrode active material (LiCo _0.9 Cr _0.1 O _{2 ± δ} ) according to Example 3 was obtained in the same manner as in Example 1 except that the firing temperature of the precursor was set to 500 ° C.

(Example 4)
A positive electrode active material (LiCo _0.85 Al _0.15 O) according to Example 4 was prepared in the same manner as in Example 1 except that the raw material composition ratio was changed to Li: Co: Al = 1: 0.85: 0.15. _{2 ± δ} ) was obtained.

(Example 5)
Except that the raw material composition ratio was Li: Co: Al = 1: 0.95: 0.05, a cathode active material (LiCo _0.95 Al _0.05 O _{2 ± δ} ) was obtained.

(Comparative Example 1)
A positive electrode active material (LiCoO _{2 ± δ} ) according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the raw material composition ratio was changed to Li: Co: Al = 1: 1: 0.

(Comparative Example 2)
A positive electrode according to Comparative Example 2 in the same manner as in Example 1 except that nickel acetate was used as a nickel source instead of the aluminum source, and that the raw material composition was Li: Co: Ni = 1: 0.9: 0.1. An active material (LiCo _0.9 Ni _0.1 O _{2 ± δ} ) was obtained.

(Comparative Example 3)
Positive electrode according to Comparative Example 3 in the same manner as in Example 1 except that chromium acetate was used as a chromium source instead of the aluminum source, and that the raw material composition was Li: Co: Cr = 1: 0.9: 0.1. An active material (LiCo _0.9 Cr _0.1 O _{2 ± δ} ) was obtained.

2. Confirmation of Crystal Phase X-ray diffraction measurement was performed on the positive electrode active materials according to Examples 1 to 5 and Comparative Examples 1 to 4 using CuKα as a radiation source, and diffraction peaks were confirmed. FIG. 4 shows the results of X-ray diffraction measurement. As is clear from the results shown in FIG. 4, diffraction peaks derived from the spinel-type crystal phase were confirmed in all of Examples 1 to 5 and Comparative Examples 1 to 4.

3. SEM observation The form of the positive electrode active materials according to Example 1 and Comparative Example 1 was observed by SEM. FIG. 5 shows the results. As shown in FIG. 5, it is considered that Example 1 has larger particles and higher crystallinity than Comparative Example 1.

4. Preparation of Electrode The obtained positive electrode active material, conductive auxiliary agent, and binder were weighed in a mass ratio of positive electrode active material: conductive auxiliary agent: binder = 85: 10: 5, and wet-mixed with NMP. A slurry was obtained. The obtained slurry was applied on an aluminum foil and dried at 120 ° C. overnight to obtain a positive electrode.

5. Preparation of Lithium Ion Battery Using the above-mentioned positive electrode, negative electrode (lithium foil), and F-substituted carbonate-based electrolyte as the electrolyte, a separator is placed between the positive and negative electrodes, and sealed in a coin-type battery together with the electrolyte. A lithium ion battery (CR2032 coin cell) for evaluation was obtained.

6. Charge / Discharge Test A charge / discharge test was performed on the produced lithium ion battery under the following conditions, and the Coulomb efficiency in the first charge / discharge cycle after charging at 4.45 V was confirmed.
CC charge: current 0.1C, termination condition 4.45V
CC discharge: current 0.1C, termination condition 2.5V

  The results are shown in Table 1 below. FIG. 6 shows charge / discharge curves for Example 1 and Comparative Example 1 for reference.

  As is clear from the results shown in Table 1, Examples 1 to 5 have significantly increased initial coulomb efficiency than Comparative Examples 1 to 3. As shown in FIGS. 4 and 5, it is considered that the crystallinity of the spinel-type crystal phase was increased and the spinel-type crystal phase was stabilized by aluminum doping. As shown in FIG. 6, the average voltage of Example 1 was higher than that of Comparative Example 1 by about 0.13 V. It is considered that aluminum doping increased the crystallinity of the spinel-type crystal phase and increased the electron conductivity.

  From the above results, it can be seen that, when a certain amount of aluminum is substituted for a part of the spinel-type lithium cobaltate with a specific amount of aluminum, superior performance can be exhibited as the positive electrode active material of the lithium-ion battery rather than the spinel-type lithium cobaltate. Do you get it.

  In addition, although the said Example showed Examples 1-5 whose aluminum substitution amount is 0.05-0.15, the positive electrode active material of this indication is not limited to this form. As described above, the technology of the present disclosure has found the effectiveness of substituting some elements of spinel-type lithium cobalt oxide with aluminum, and even when the aluminum substitution amount is less than 0.05. It is considered that a desired effect can be exhibited as compared with the case where the aluminum substitution amount is 0.

  In the above example, the molar ratio between lithium and the other metal was adjusted to be 1. However, the molar ratio of the other metal to lithium was limited to this as long as a spinel-type crystal phase was obtained. is not. According to the knowledge of the present inventors, a sufficient effect can be exhibited when the molar ratio of the other metal to Li is more than 0.85 and 1.15 or less.

  The lithium ion battery using the positive electrode active material according to the present invention can be widely used, for example, from a small power supply for a portable device to a large power supply for a vehicle.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Electrolyte layer 10 Lithium ion battery

Claims (1)

Having a spinel-type crystal phase containing lithium, cobalt, aluminum, and oxygen,
LiCo _x Al _y O having a composition represented by _{2 ± δ (0.85 ≦ x <} 1,0 <y ≦ 0.15,0.85 <x + y ≦ 1.15),
Cathode active material for lithium ion batteries.