JP2004175609A - Lithium cobaltate used for positive electrode of lithium ion battery, its manufacturing process and lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion battery which shows a high charging voltage and an excellent cycle characteristic and realizes high capacity and long service life. <P>SOLUTION: Modified lithium cobaltate contains MO<SB>x</SB>(wherein M is zirconium, titanium, boron, aluminum or gallium; and x is 2 when M is zirconium or titanium, and x is 3/2 when M is boron, aluminum or gallium) deposited onto the surface of a lithium cobaltate particle. The lithium ion battery uses this as a positive electrode active material. The modified lithium cobaltate is obtained through a manufacturing process employing an extremely simple treatment wherein the lithium cobaltate particle is soaked into an aqueous solution and subsequently baked. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium cobalt oxide (LiCoO ₂ ) having a layered rock salt type (α-NaFeO ₂ type) structure, and a lithium ion battery having a positive electrode containing the lithium cobalt oxide. The present invention further relates to a method for producing the above-mentioned lithium cobaltate.
[0002]
[Prior art]
At present, with the miniaturization and cordlessness of portable electronic and electrical devices such as mobile phones and notebook computers, lithium-ion batteries have already been used as a driving power supply for their outstanding high voltage and high energy density due to their outstanding high voltage and high energy density. It has been put to practical use and has spread widely. On the other hand, also in the field of automobiles, early commercialization of electric vehicles is desired due to environmental problems such as air pollution and increase of carbon dioxide, and the use of lithium ion batteries as power sources for electric vehicles has been studied. I have.
[0003]
Transition metal oxides having a hexagonal layered crystal structure are known to be capable of introducing metal ions of a suitable size into the lattice sites and / or interstitial spaces of the crystal. In particular, the lithium intercalation compound can introduce lithium ions under a specific potential difference between crystal lattice sites and / or interstitial spaces and take them out again. Therefore, the lithium composite oxide is used as a positive electrode active material of a lithium ion battery. It's being used.
[0004]
In addition, lithium cobalt oxide, lithium manganate (LiMnO ₂ ), lithium nickel oxide (LiNiO ₂ ), and the like are generally known as a positive electrode material useful for a high-energy type lithium ion battery having a voltage of 4 V class. However, among them, lithium cobalt oxide is advantageous in that it has high voltage and high capacity.
[0005]
However, even when lithium cobalt oxide is used as a positive electrode active material of a lithium ion battery, when charge and discharge are repeated at a charging voltage of 4.2 V or more using a carbonaceous material as a negative electrode active material, the capacity is significantly reduced, or However, the internal pressure of the battery rises due to the decomposition of the electrolyte, which leads to liquid leakage or the opening of the safety valve.To prevent this, an expensive and strict voltage control electronic circuit is required. There was a problem of becoming.
[0006]
In order to solve the above-mentioned problem, a modified lithium cobaltate in which cobalt atoms of lithium cobaltate are replaced by trace amounts of iron and manganese atoms is known (for example, see Patent Document 1). However, the manufacturing process is complicated, and the effect of improving the long-term charge / discharge cycle characteristics has not been clarified.
[0007]
Further, lithium cobalt oxide is usually produced by firing a mixture of cobalt acid (Co ₃ O ₄ ) and lithium carbonate (Li ₂ Co ₃ ) at 700 to 900 ° C. in the air. One attempt to reduce the high production cost of baking is to create materials at lower temperatures. However, for example, the operating voltage of a lithium ion battery when a sample synthesized at around 400 ° C. is used as a positive electrode material is about 3.5 V, and when a positive electrode material synthesized at 850 ° C. is used (3.8 to 4 V). ), The performance of the battery has been a problem when used as it is in a lithium ion battery.
[0008]
In order to solve the above-mentioned problems, a hydrothermal oxidation method for producing lithium cobaltate having a layered rock salt type structure at an extremely low temperature of 105 to 300 ° C. is known (for example, see Patent Document 2). ). However, the hydrothermal oxidation process is relatively complicated, and the improvement of the charge / discharge cycle characteristics thereby is not sufficient.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-37630 [Patent Document 2]
US Pat. No. 6,399,041
[Problems to be solved by the invention]
Under such circumstances, when used as a positive electrode of a lithium-ion battery, it has a layered rock-salt type structure that increases the charge voltage of the battery, has good charge / discharge cycle characteristics, and thus can be expected to have a long life. The development of modified lithium cobaltate is desired. Also, a method for producing the above-mentioned lithium cobalt oxide at low cost by a simpler treatment is desired.
[0011]
[Means for Solving the Problems]
Here, the present inventors use a modified lithium cobaltate containing lithium cobaltate particles and an oxide of an element other than cobalt formed on the surface of the particles as a positive electrode active material of a lithium ion battery, thereby obtaining a charge voltage. Was found to be able to be increased to 4.4 V and the discharge capacity could be maintained well, and the present invention was completed. Further, they have found that the modified lithium cobaltate of the present invention can be obtained by a very simple treatment of impregnating lithium cobaltate particles in an aqueous solution containing the ions of the element and then firing the same, thereby completing the present invention.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
[0013]
In the first aspect of the present invention, the lithium cobalt oxide particles and MO _x (M is zirconium, titanium, boron, aluminum or gallium attached on the surface of the particles, x is 2 when M is zirconium or titanium, X is 3/2 when M is boron, aluminum or gallium).
[0014]
By using the modified lithium cobaltate of the present invention as a positive electrode active material of a lithium ion battery, the charging voltage can be increased to 4.4 V, and the discharge capacity can be well maintained.
[0015]
In the conventional lithium cobalt oxide, when charge and discharge are repeated at a charge voltage of 4.2 V or more with respect to a lithium metal electrode using a carbonaceous material as a negative electrode active material, the charge / discharge cycle characteristics are remarkably deteriorated. The internal pressure of the battery increases with the decomposition of the battery, which leads to liquid leakage or breakage of the safety valve. To prevent this, an expensive and strict voltage control electronic circuit is required, and the battery can be reduced in size and weight. On the other hand, power supply costs are high.
[0016]
According to the modified lithium cobaltate of the present invention, a stable discharge capacity can be obtained even when charging is repeatedly performed at a voltage of 4.4 V with respect to a lithium metal electrode, and cannot be achieved with conventional lithium cobaltate. High capacity can be achieved. For example, the conventional lithium cobalt oxide has a discharge capacity of about 150 mAh / g at 4.3 V charge, whereas the lithium cobalt oxide of the present invention allows a charge of 4.4 V and a discharge capacity of 170 mAh / g or more. It becomes.
[0017]
In the present invention, “MO _x ” refers to an oxide of zirconium, titanium, boron, aluminum, or gallium, and more specifically, zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), or boron oxide (B ₂ O ₃ ), aluminum oxide (Al ₂ O ₃ ), or gallium oxide (Ga ₂ O ₃ ).
[0018]
Modified lithium cobaltate of the present invention includes a lithium cobaltate particles, on the surface of the particle, characterized in that the above-mentioned MO _x is attached.
[0019]
Lithium cobaltate particles of the present invention, and the MO _x adhered to the lithium cobalt oxide particles, their particle size is not particularly limited, and may but be of any size, lithium cobaltate particles Is preferably 0.01 to 50 μm, and particularly preferably 1 to 20 μm. As for the MO _x attached to the lithium cobalt oxide particles, preferably those having a particle diameter of 0.01 m to 50 m, that of 1~20μm is particularly preferred.
[0020]
In the present invention, MO _X is may be any weight ratio with respect to lithium cobalt oxide, the MO _x on the final modified lithium cobaltate is contained 0.5 to 15 wt% Is preferably contained in an amount of 1 to 5% by mass, particularly preferably about 1% by mass. Modified lithium cobaltate in MO _x of less than 0.5 wt% does not substantially change, whereas the modified lithium cobaltate is used in the positive electrode contains 15 wt% of MO _x, this This is because the performance of a lithium ion battery using such a modified lithium cobaltate as the positive electrode active material is adversely affected. Also, may be included lithium cobalt oxide particles during the modified lithium cobaltate unattached of the deposited lithium cobalt oxide particles and MO _x of MO _x of the present invention, also, the modified lithium cobaltate of the present invention The composition is not limited to these, and may include other unavoidable impurities.
[0021]
Further, the most preferred form of the present invention is to use ZrO ₂ or B ₂ O ₃ as MO _x . By using the modified lithium cobaltate as a positive electrode active material of a lithium ion battery, the charging voltage can be increased to 4.4 V, and the charge / discharge cycle characteristics can be improved.
[0022]
A second aspect of the present invention is a modification of the present invention comprising impregnating lithium cobaltate particles with an aqueous solution containing zirconium, titanium, boron, aluminum or gallium ions and calcining the resulting impregnated lithium cobaltate particles. This is a method for producing lithium cobaltate.
[0023]
According to the production method of the present invention, the modified lithium cobaltate of the present invention, which is useful as a positive electrode active material of a lithium ion battery, can be produced extremely easily.
[0024]
Conventionally, various approaches have been made to lithium cobalt oxide in order to provide a positive electrode active material having better performance such as charge-discharge cycle characteristics. For example, there are a method of obtaining a composite oxide by mixing with a transition metal other than cobalt and baking it, and a method of producing lithium cobalt oxide at a low temperature by a hydrothermal oxidation method. However, none of these methods has shown a remarkable improvement in performance such as the final charge voltage and charge / discharge cycle characteristics, and the methods themselves were generally complicated.
[0025]
According to the production method of the present invention, lithium cobaltate particles are impregnated with an aqueous solution containing ions of zirconium, titanium, boron, aluminum or gallium (hereinafter also referred to as “M ions”), and the resulting impregnated lithium cobaltate is produced. The modified lithium cobaltate of the present invention, which can be used as a positive electrode active material having excellent performance such as charge / discharge cycle characteristics, can be produced by a very simple method of firing particles. Said elements by firing occurs is oxidized MO _x is believed to be due to the formation on the surface of the lithium cobalt oxide particles.
[0026]
In the present invention, lithium cobaltate is not particularly limited, and can be produced by a generally known method or purchased and used commercially. Process for the preparation of lithium cobalt oxide is generally well known, for example, particles of lithium carbonate _(Li 2 CO ₃₎ and cobalt oxide _(Co 3 _{O 4)} were mixed, the resulting mixture at 600 to 900 ° C. 5 to 25 Lithium cobaltate is produced by calcining at 800 ° C. for 10 hours.
[0027]
As the form of the aqueous solution used for impregnation is not particularly limited as long as MO _x can adhere to the surface of the lithium cobalt oxide after firing, zirconium suitable form, titanium, boron, an aqueous solution containing aluminum or gallium Can be used. Examples of the form of these metals (including boron) include zirconium, titanium, boron, aluminum or gallium oxynitrate, nitrate, acetate, sulfate, carbonate, hydroxide, acid and the like. Since the most preferred form of the modified lithium cobaltate of the present invention uses ZrO ₂ or B ₂ O ₃ as MO _x , the M ions are more preferably zirconium ions or boron ions, and the aqueous solution containing M ions the example, ZrO _{(NO 3) 2 solution, ZrCO 4 · ZrO 2 · 8H} 2 O aqueous solution, Zr _{(SO 4)} is more preferably used such as _two aqueous solutions or _H 3 BO ₃ aqueous solution, among others ZrO _(NO 3) Most preferably, an aqueous solution of H ₂ or H ₃ BO ₃ is used. The concentration of the M ion aqueous solution is not particularly limited, but a saturated solution is preferable because the volume of the solution can be reduced in the impregnation step. In the present invention, as the forms in an aqueous solution of M ions, not only ions of M single element, the ions are bonded to other element state, for example in terms of the boron B (OH) ₄ ^-, etc., Including.
[0028]
In the production method of the present invention, when the lithium cobaltate is impregnated with the aqueous M ion solution, the mass ratio between the lithium cobalt oxide and the aqueous M ion solution is not particularly limited, and the modified lithium cobalt oxide to be produced is not limited to the above. The mass ratio may be set according to the composition. The impregnation time only needs to be a time during which the impregnation is sufficiently performed, and the impregnation temperature is not particularly limited.
[0029]
Further, the production method of the present invention includes firing the particles generated by the impregnation. In this step, the calcination temperature and the calcination time can be appropriately determined within a range appropriate for the calcination, but the calcination is preferably performed at 400 to 800 ° C. for 1 to 5 hours, particularly preferably at 600 ° C. for 3 hours. The firing may be performed under an oxygen stream or in the air. Further, the particles generated by the impregnation may be fired as they are, but it is preferable to dry the particles before firing in order to remove moisture in the mixture. Here, the drying can be performed by a generally known method, and for example, heating in an oven, hot-air drying, or the like can be used alone or in combination. The drying is preferably performed in an atmosphere such as oxygen or air.
[0030]
The modified lithium cobaltate thus obtained may be pulverized if necessary.
[0031]
When a lithium ion battery is manufactured using the modified lithium cobaltate manufactured by the above method as a positive electrode active material and lithium metal as a negative electrode, the charge and discharge voltage is 3.0 to 4.0 as described later. According to the production method of the present invention, a lithium ion battery having extremely excellent characteristics has an initial discharge capacity of 170 mAh / g or more at 4 V and a discharge capacity at the 100th cycle of charge and discharge of 80% or more of the initial value. Can be.
[0032]
A third aspect of the present invention is a lithium ion battery having a positive electrode including the modified lithium cobaltate of the present invention.
[0033]
By using the modified lithium cobaltate of the present invention for a positive electrode, a lithium ion battery having excellent characteristics can be obtained.
[0034]
As described above, the lithium ion battery of the present invention is characterized in that the modified lithium cobalt oxide of the present invention is used as a positive electrode active material, and other components (eg, a negative electrode active material, an electrolyte, etc.) Known ones can be used.
[0035]
The performance of lithium cobalt oxide as a positive electrode active material was evaluated by preparing a lithium ion battery using a generally known method, charging and discharging at a constant current in an appropriate potential range, and measuring its electric capacity. can do. In addition, it is possible to judge whether the cycle characteristics are good or not from a change in electric capacity due to repeated charging and discharging.
[0036]
In the lithium ion battery of the present invention, the preferred working voltage range for repeated charging and discharging is in the range of 3.0 to 4.4 V, but the conventional operating voltage is controlled at an upper limit voltage of 4.2 or 4.1 V per cell. It can also be charged and used with a charger.
[0037]
The lithium-ion battery of the present invention includes, for example, electronic devices such as a notebook computer, a mobile phone, a cordless phone handset, a video movie, an LCD TV, an electric shaver, a mobile radio, a headphone stereo, a backup power supply and a memory card, a pacemaker, and a hearing aid. Medical devices, and automobiles.
[0038]
【Example】
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
[0039]
Comparative Example 1: Unmodified LiCoO ₂
3.879 g of lithium carbonate (Li ₂ CO ₃ , manufactured by SQM Co., purity 99%) and 8.026 g of cobaltic acid (Co ₃ O ₄ , manufactured by THE HALL CHEMICAL CO., Purity 99%) were put in a mill ball. After mixing for 30 minutes, the mixture was placed in a crucible and fired in an oven at 800 ° C. for 10 hours. Next, the calcined product was pulverized by a generally known method to obtain lithium cobaltate (LiCoO ₂ ) particles having a particle diameter passing through a sieve of 400 mesh.
[0040]
Example _1: LiCoO ₂ -ZrO 2
90% of the particles of lithium cobaltate (LiCoO ₂ ) produced in Comparative Example 1 having a particle size distribution smaller than 17 μm were converted to ZrO (NO ₃ ) ₂ .xH ₂ O (molecular weight 231.23, manufactured by ALDRICH, Inc.). ) Was impregnated into 20 mL of an aqueous solution containing 0.1 g. The mixture was dried at 110 ° C. and then the dried mixture was calcined at 600 ° C. for 3 hours. The calcined product was pulverized by a generally known method to be used as a raw material for a positive electrode of a lithium ion battery.
[0041]
FIG. 1 shows a photograph of lithium cobaltate particles before modification taken by a scanning electron microscope. As can be seen from FIG. 1, the lithium cobaltate particles before modification have a substantially flat surface. Furthermore, as shown in FIG. 2, the lithium cobaltate particles before modification show peaks only in oxygen and cobalt in the energy dissipation spectrum.
[0042]
FIG. 3 shows a photograph of the modified lithium cobaltate particles taken with a scanning electron microscope. As can be seen from FIG. 3, a substance is attached to the surface of the modified lithium cobalt oxide particles. Further, as shown in FIG. 4, the modified lithium cobaltate particles show peaks in zirconium in addition to oxygen and cobalt peaks in the energy dissipation spectrum. From this, it is considered that ZrO ₂ is attached to the surface of the modified lithium cobaltate particles.
[0043]
Example _2: LiCoO 2 -B 2 O ₃
Modified using the same method as in Example 1 except that boric acid powder (H ₃ BO ₃ , molecular weight 61.83, manufactured by ALDRICH, Inc.) was used instead of ZrO (NO ₃ ) ₂ .xH ₂ O. Lithium cobaltate was prepared and pulverized.
[0044]
Test example 1:
The modified lithium cobaltate obtained in Examples 1 and 2, the unmodified lithium cobaltate obtained in Comparative Example 1, and a commercially available lithium cobaltate (manufactured by Nippon Chemical Industrial Co.) as a positive electrode, and metal lithium as a negative electrode Using a 1 M LiPF ₆ solution in a mixed solvent containing ethylene carbonate and dimethyl carbonate as electrolytes, three types of 2032 type button lithium ion batteries were produced.
[0045]
For these batteries, the charge / discharge characteristics at a charge / discharge rate of 0.2 C (current density 28 mA / g) were measured. A lithium ion battery having a positive electrode made of a commercially available lithium cobalt oxide has a 20% longer battery life when charged and discharged at 3 to 4.4 V than at 3 to 4.2 V. However, as shown by the curve (c) in FIG. 5, after about 70 cycles of charging / discharging, the discharge capacity of the lithium ion battery was reduced to less than 80% of the initial discharge capacity. Further, as shown by the curve (d) in FIG. 5, the lithium ion battery having the positive electrode made of the unmodified lithium cobalt oxide of Comparative Example 1 dropped to less than half of the initial discharge capacity in less than 30 cycles. Similar test conditions in (charged and discharged between the 3~4.4V), curves of Figure 5 the performance of a lithium-ion battery having a cathode comprising a modified lithium cobaltate -MO _x of the present invention (a) and (b) It was shown to. When M was boron, as shown by the curve (a), even after 100 cycles of charging / discharging, the discharge capacity maintained a level of 90% or more of the initial value. When M was zirconium, the level was maintained at 80% or more of the initial discharge capacity as shown by the curve (b).
[0046]
【The invention's effect】
By using the modified lithium cobaltate of the present invention as a positive electrode active material, a lithium ion battery exhibiting a high charging voltage of 4.4 V and excellent cycle characteristics, and achieving high capacity and long life can be obtained. Further, according to the production method of the present invention, the modified lithium cobalt oxide of the present invention suitable for a positive electrode material of a lithium ion battery can be obtained by an extremely simple treatment.
[Brief description of the drawings]
FIG. 1 is a view showing a photograph of lithium cobaltate particles taken with a scanning electron microscope.
FIG. 2 is a diagram showing an energy dissipation spectrum of lithium cobaltate particles.
FIG. 3 is a view showing a photograph of the modified lithium cobaltate particles produced in Example 1 taken by a scanning electron microscope.
FIG. 4 is a view showing an energy dissipation spectrum of the modified lithium cobaltate particles produced in Example 1.
FIG. 5 is a diagram in which the discharge capacity is plotted against the number of charge / discharge cycles. Here (a) shows a lithium ion battery using a modified lithium cobaltate -B ₂ O ₃ in the positive electrode, (b) shows a lithium ion battery using a modified lithium cobaltate -ZrO ₂ in the positive electrode, (c () Shows a lithium ion battery using a commercially available lithium cobalt oxide for the positive electrode, and (d) shows a lithium ion battery using the unmodified lithium cobalt oxide prepared in Comparative Example 1 for the positive electrode.

Claims (9)

Lithium cobaltate particles and MO _x (M is zirconium, titanium, boron, aluminum or gallium deposited on the surface of the particles, x is 2 when M is zirconium or titanium, M is boron, aluminum or gallium Wherein x is 3/2.). The MO _X comprises 0.5 to 15% by weight relative to the modified lithium cobaltate, modified lithium cobaltate of claim 1. The modified lithium cobaltate according to claim 1, wherein said MO _X is ZrO ₂ or B ₂ O ₃ . The method according to any one of claims 1 to 3, comprising impregnating the lithium cobaltate particles with an aqueous solution containing ions of zirconium, titanium, boron, aluminum or gallium, and calcining the resulting impregnated lithium cobaltate particles. A method for producing the modified lithium cobaltate described above. Impregnating the lithium cobalt oxide particles ZrO (NO _{3) 2} aqueous solution or an aqueous boric acid solution, a manufacturing method of claim 4. The production method according to claim 4, wherein the calcination is performed at 400 to 800 ° C. for 1 to 5 hours. The production method according to claim 6, wherein the calcination is performed at 600 ° C for 3 hours. The method according to claim 6, further comprising drying the particles generated by the impregnation before firing. A lithium ion battery having a positive electrode containing the modified lithium cobaltate according to claim 1.

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