KR20030073168A - Positive active material for lithium secondary battery and lithium secondary battery comprising the same - Google Patents

Abstract

PURPOSE: Provided are a cathode active material for lithium secondary battery, which has an excellent life property, and which is safe when overcharged, and a lithium secondary battery comprising the same. CONSTITUTION: The cathode active material comprises a cobalt-based or nickel-based lithium intercalation compound selected from the group consisting of the following(1)-(9); and a lithium-containing manganese-based compound surface-treated with hydroxyl group(OH). LixCo1-yM'yA2(1); LixCo1-yM'yO2-zXz(2); LixNi1-yM'yA2(3); LixNi1-yM'yO2-zXz(4); LixNi1-yCoyO2-zXz(5); LixNi1-y-zCoyM'zAα(6); LixNi1-y-zCoyM'zO2-αXα(7); LixNi1-y-zMnyM'zAα(8); LixNi1-y-zMnyM'zO2-αXα (9). In the formulas, 0.95<=x<=1.1, 0<=y<=0.5, 0<=z<=0.5, 0<=α<=2, M' is at least one element selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or rare earth elements, A is an element selected from the group consisting of O, F, S and P, and X is an element selected from the group consisting of F, S, and P.

Description

Anode active material for a lithium secondary battery and a lithium secondary battery including the same {POSITIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

[Industrial use]

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a positive electrode active material for a lithium secondary battery having excellent safety and life characteristics even when overcharged and a lithium secondary battery including the same.

[Prior art]

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing. Lithium secondary batteries, which are commercially available and used, are the elements of the heart of the digital age, which are rapidly being applied to portable phones, notebook computers, camcorders, etc., which have an average discharge potential of 3.7V, that is, 3C as 3C.

In addition to improving battery capacity and performance characteristics, studies are being actively conducted to improve safety such as overcharging characteristics. When the battery is overcharged, depending on the state of charge, lithium is excessively precipitated at the positive electrode, lithium is excessively inserted at the negative electrode, and the positive electrode and negative electrode are thermally unstable, causing rapid exothermic reactions such as decomposition of the organic solvent in the electrolyte and thermal runaway phenomenon. Occurs, a serious problem occurs in the safety of the battery.

In order to improve the overcharge characteristics of the lithium secondary battery, US Patent No. 5,827,332 discloses a method of improving the overcharge characteristics of a lithium secondary battery by treating the surface with an alkali metal chalcogenide compound.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a cathode active material for a lithium secondary battery which is safe even when overcharged and excellent in life characteristics.

Another object of the present invention is to provide a lithium secondary battery including the positive electrode active material for the lithium secondary battery.

1 is a cross-sectional view of a rectangular lithium secondary battery.

2A to 2C are graphs showing overcharge characteristics of the batteries of Example 1, Comparative Example 1, and Comparative Example 2. FIG.

In order to achieve the above object, the present invention is a cobalt-based or nickel-based lithium intercalation compound selected from the group consisting of the following formula (1) to (9); And it provides a cathode active material for a lithium secondary battery comprising a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH).

Li _x Co _1-y M ' _y A ₂ (1)

Li _x Co _1-y M ' _y O _2-z X _z (2)

Li _x Ni _1-y M ' _y A ₂ (3)

Li _x Ni _1-y M ' _y O _2-z X _z (4)

Li _x Ni _1-y Co _y O _2-z X _z (5)

Li _x Ni _1-yz Co _y M ' _z A _α (6)

Li _x Ni _1-yz Co _y M ' _z O _2-α X _α (7)

Li _x Ni _1-yz Mn _y M ' _z A _α (8)

Li _x Ni _1-yz Mn _y M ' _z O _2-α X _α (9)

Wherein 0.95 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M ′ is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or At least one element selected from the group consisting of rare earth elements, A is an element selected from the group consisting of O, F, S and P and X is an element selected from the group consisting of F, S and P.)

The present invention also provides a lithium secondary battery comprising the positive electrode active material for the lithium secondary battery.

Hereinafter, the present invention will be described in more detail.

The structure of the general non-aqueous lithium secondary battery 1 is as shown in FIG. The battery uses a lithiated intercalation compound as a positive electrode (2) and a negative electrode (4), inserts a separator (6) between the positive electrode (2) and the negative electrode (4) and wound the electrode assembly (8). After forming it is put into the case 10 is manufactured. The top of the battery is sealed with a cap plate 12 and a gasket 14. The battery cap plate 12 may be provided with a safety vent 16 to prevent overpressure of the battery. The positive electrode tab 18 and the negative electrode tab 20 are respectively installed in the positive electrode 2 and the negative electrode 4, and insulators 20 and 22 are inserted to prevent internal short circuit of the battery. In addition, the electrolyte solution 26 is injected before sealing the battery. The injected electrolyte solution 26 is impregnated into the separator 6.

The lithium secondary battery may have a thermal runaway phenomenon in which the temperature of the battery rapidly rises due to overcharge or short circuit due to a design defect of the battery itself due to misuse or failure of a charger. In particular, during overcharging, excess lithium is released from the anode and precipitates on the surface of the cathode, resulting in two electrodes thermally very unstable, resulting in thermal decomposition of the electrolyte, reaction between the electrolyte and lithium, oxidation of the electrolyte at the anode, and thermal decomposition of the cathode active material. The exothermic reaction proceeds abruptly by the reaction of oxygen and electrolyte generated by the so-called so-called thermal runaway phenomenon in which the temperature of the battery rises rapidly, leading to the ignition and smoke of the battery exceeding the maximum allowable temperature of the battery.

The present invention is a cobalt-based or nickel-based lithium intercalation compound selected from the group consisting of the following formulas (1) to (9); And using a positive electrode active material for a lithium secondary battery containing a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH) provides a lithium secondary battery safe even when overcharged.

Li _x Co _1-y M ' _y A ₂ (1)

Li _x Co _1-y M ' _y O _2-z X _z (2)

Li _x Ni _1-y M ' _y A ₂ (3)

Li _x Ni _1-y M ' _y O _2-z X _z (4)

Li _x Ni _1-y Co _y O _2-z X _z (5)

Li _x Ni _1-yz Co _y M ' _z A _α (6)

Li _x Ni _1-yz Co _y M ' _z O _2-α X _α (7)

Li _x Ni _1-yz Mn _y M ' _z A _α (8)

Li _x Ni _1-yz Mn _y M ' _z O _2-α X _α (9)

Wherein 0.95 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M ′ is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or At least one element selected from the group consisting of rare earth elements, A is an element selected from the group consisting of O, F, S and P and X is an element selected from the group consisting of F, S and P.)

As the lithium-containing manganese-based compound, LiMn ₂ O ₄ is preferable.

Lithium-containing manganese-based compounds have a spinel structure, and thus have excellent thermal safety compared to other cathode active materials for lithium secondary batteries. Therefore, a lithium-containing manganese compound surface-treated with a hydroxyl group (OH) may be added to the cobalt-based or nickel-based lithium intercalation compounds of Formulas (1) to (9) to manufacture a battery that is safe even when overcharged.

When the lithium-containing manganese-based compound is mixed with the lithium intercalation compound without surface treatment with a hydroxyl group (OH), the manganese-based material decomposes into MnO ₂ during overcharging and acts as a catalyst during overcharging to decompose the positive electrode active material. This accelerates the reaction with the electrolyte and causes the battery to ignite and explode.

However, as in the present invention, when the lithium-containing manganese-based compound is surface treated with a hydroxyl group (OH), the hydroxyl group and manganese are adsorbed and combined with each other during overcharging so that there is no place where decomposition reaction of the electrolyte occurs, and the hydroxylation is caused by heat during overcharging. The separator is shut down by a small amount of heat generated during the dissociation of ions, thereby making it possible to manufacture a battery that is safe even when overcharged.

In order to prepare a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH), a mixed aqueous solution of a compound capable of providing a hydroxyl group such as a lithium-containing manganese-based compound and LiOH is prepared.

Ethanol is added to disperse the active material in the aqueous solution to prepare a final solution. A lithium-containing manganese compound is added to the final solution and the final solution is stirred at 1000 rpm for about 1 hour. After stirring, the stirred final solution was placed in a drying oven, dried at 250 ° C. for 10 hours, and then ground to prepare a lithium-containing manganese-based compound that was surface-treated with hydroxyl (OH).

The weight ratio of hydroxyl group (OH) in the lithium-containing manganese-based compound surface-treated with the hydroxyl group (OH) is preferably 0.1 to 10% by weight.

When the weight ratio of the hydroxyl group (OH) is less than 0.1% by weight, the effect of modifying the surface of the lithium-containing manganese-based compound with the hydroxyl group is insignificant, and when it exceeds 10% by weight, lithium ions cannot be smoothly moved during the charge and discharge process. There is a problem that the discharge capacity and the service life characteristics are lowered.

The positive electrode active material for a lithium secondary battery of the present invention is a weight ratio of a cobalt-based or nickel-based lithium intercalation compound selected from the group consisting of the above formulas (1) to (9) and a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH). It is preferable that it is 0.05: 0.95 to 0.5: 0.5.

If the weight ratio of the lithium-containing manganese-based compound surface-treated with hydroxyl (OH) is less than 0.5, the effect of improving the overcharge characteristic is insignificant.

The present invention also provides a lithium secondary battery comprising the electrolyte solution. The lithium secondary battery of the present invention includes a positive electrode active material, a negative electrode active material, a separator and an electrolyte.

Lithium metal or a commonly used carbonaceous material may be used as the negative electrode active material, and representative examples thereof may include crystalline graphite having good dislocation flatness and relatively good reversibility in charge and discharge processes.

As separators, all separators used in lithium secondary batteries can be used, and the separators can be shut down due to heat generated during the dissociation of hydroxyl groups (OH) that are surface-treated on lithium-containing manganese compounds during overcharge. A material, for example a separator made of polyethylene, can be preferably used.

In addition, the electrolyte generally uses a lithium salt dissolved in a non-aqueous organic solvent.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone can be used. The carbonate may be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and the ester may be n-methyl acetate, n-ethyl acetate, n-propyl acetate, or the like. Carbonate solvent in the non-aqueous organic solvent. In this case, it is preferable to use a mixture of cyclic carbonate and chain carbonate.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (CxF _{2x + 1} SO ₂ ) (CyF _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, and LiI can be used by mixing one or two or more selected from the group consisting of Do.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

(Example 1)

An aqueous solution of 10% LiOH was prepared so as to be 5% by weight relative to LiMn ₂ O ₄ . In order to disperse the active material in this aqueous solution, 50 ml of ethanol was added to 1 kg of the active material to prepare a final solution. LiMn ₂ O ₄ was added to the final solution, and the final solution was stirred at 1000 rpm for 1 hour. After stirring, the stirred final solution was placed in a drying oven, dried at 250 ° C. for 10 hours, and then ground to prepare a LiMn ₂ O ₄ compound surface-treated with a hydroxyl group (OH).

Slurry was prepared by adding 2% by weight of carbon black and 2% by weight of polyvinylidene fluoride (PVDF) to a powder in which the prepared LiMn ₂ O ₄ compound and LiCoO ₂ were mixed at a weight ratio of 3: 7. The slurry was applied on aluminum foil, dried and rolled with a roll press to prepare a positive electrode plate. 2 wt% of graphite and polyvinylidene fluoride (PVDF), which are negative electrode active materials, were mixed and dissolved in NMP to prepare a slurry. The slurry was applied to a copper current collector, dried, and rolled in a roll press to prepare a negative electrode plate. A porous separator composed of three layers of polyethylene (PE) / polypropylene (PP) / polyethylene (PE) is inserted between the positive electrode plate and the negative electrode plate, and the positive electrode plate, the negative electrode plate, and the separator are inserted into an aluminum can and the top of the can. After the welding, a 1.15 M LiPF ₆ EC: EMC: PC: FB electrolyte was injected into the can and 3.0 g was sealed to prepare a battery.

(Example 2)

A battery was manufactured in the same manner as in Example 1, except that a powder in which the LiMn ₂ O ₄ compound surface-treated with a hydroxyl group (OH) and LiCoO ₂ was mixed at a weight ratio of 5: 5.

(Comparative Example 1)

A battery was manufactured in the same manner as in Example 1, except that LiMn ₂ O ₄ , which was not surface-treated with hydroxyl group (OH), was used instead of the LiMn ₂ O ₄ compound surface-treated with hydroxyl group (OH).

(Comparative Example 2)

A battery was manufactured in the same manner as in Example 1, except that 2 wt% of carbon black and 2 wt% of polyvinylidene fluoride (PVDF) were added to LiCoO ₂ to prepare a slurry.

The battery of Example 1, Comparative Example 1 and Comparative Example 2 was overcharged at a voltage of 12V at 1C to measure the change in voltage and temperature of the battery over time, and the results are shown in FIGS. 2A to 2C. As shown in Figure 2a, the battery of Example 1 was found to rise in temperature after 20 minutes after overcharge. In addition, the temperature of the battery gradually increased and the voltage remained stable without dropping at 12V. On the contrary, in Comparative Examples 1 and 2, the temperature of the battery rapidly increased and the voltage rose to 12V and then dropped to 0V.

A lithium intercalation compound selected from the group consisting of the above formulas (1) to 9 of the present invention; And a lithium secondary battery comprising a positive electrode active material containing a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH) is safe even when overcharged and has excellent life characteristics.

Claims (4)

Cobalt-based or nickel-based lithium intercalation compounds selected from the group consisting of the following formulas (1) to (9); And a lithium-containing manganese-based compound surface-treated with a hydroxyl group (OH). Li _x Co _1-y M ' _y A ₂ (1) Li _x Co _1-y M ' _y O _2-z X _z (2) Li _x Ni _1-y M ' _y A ₂ (3) Li _x Ni _1-y M ' _y O _2-z X _z (4) Li _x Ni _1-y Co _y O _2-z X _z (5) Li _x Ni _1-yz Co _y M ' _z A _α (6) Li _x Ni _1-yz Co _y M ' _z O _2-α X _α (7) Li _x Ni _1-yz Mn _y M ' _z A _α (8) Li _x Ni _1-yz Mn _y M ' _z O _2-α X _α (9) Wherein 0.95 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M ′ is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V or At least one element selected from the group consisting of rare earth elements, A is an element selected from the group consisting of O, F, S and P and X is an element selected from the group consisting of F, S and P.) The cathode active material according to claim 1, wherein the weight ratio of hydroxyl group (OH) in the lithium-containing manganese compound surface-treated with the hydroxyl group (OH) is 0.1 to 10% by weight. The weight ratio of the lithium intercalation compound selected from the group consisting of the formulas (1) to (9) and the lithium-containing manganese compound surface-treated with a hydroxyl group (OH) is 0.05: 0.95 to 0.5: 0.5. Positive electrode active material. A lithium secondary battery comprising the cathode active material of any one of claims 1 to 3.