JP2002260654A - Spinel-type positive electrode material for lithium secondary battery, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spinel-type positive electrode material for a lithium secondary battery having superior high temperature characteristics. SOLUTION: In this manufacturing method of the spinel-type positive material for the lithium secondary battery, a mixture, formed by mixing a lithium compound and a manganese compound, is annealed at 300-400 deg.C after it is heat- treated in the range of 900-1,200 deg.C it is then cooled down to an ordinary temperature, and a cooling speed to cool it from 500 deg.C to 300 deg.C is set at 5 deg.C/hr or less. The spinel-type positive electrode material obtained by the method has a pH of 6-9, and is used for the lithium secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a spinel type positive electrode material for a lithium secondary battery, and the obtained positive electrode material
Further, the present invention relates to a lithium secondary battery using the same, and more particularly, to a method for producing a spinel-type positive electrode material for a lithium secondary battery having excellent high-temperature characteristics, the obtained positive electrode material, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, portable personal computers and telephones have become portable.
With the rapid progress of cordless technology, the demand for secondary batteries as power sources for driving them is increasing. Among them, lithium secondary batteries are particularly expected because of their small size and high energy density. As the positive electrode material of the lithium secondary battery, there are lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4) and the like. Since these composite oxides have a voltage of 4 V or more with respect to lithium, a battery having a high energy density is obtained.

However, supply of lithium cobaltate may be short in the future due to the high cost of cobalt and the small reserves. On the other hand, recently, attention has been paid to spinel-based lithium manganate as a cathode material that is inexpensive, has abundant reserves, and can store and release lithium at the same high voltage as lithium cobalt oxide. ing. However, the spinel-based lithium manganate obtained by a normal calcination method has a high pH of 9 or more, and has problems of battery gas generation and poor high-temperature characteristics. In order to improve this, mixing and firing have been repeated. However, this method has a problem that the manufacturing cost is increased.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a positive electrode material for a lithium secondary battery having excellent high-temperature characteristics, an inexpensive manufacturing method, and a lithium secondary battery using the same.

[0005]

Means for Solving the Problems The present inventors diligently studied the influence of the manufacturing method on the pH reduction of the positive electrode material for a lithium secondary battery, and found that the temperature condition at 300 to 400 ° C. The present invention has been found to have a close relationship with the pH reduction of the positive electrode material for use in the present invention, and has reached the present invention. Therefore, the present invention provides a spinel-type positive electrode for a lithium secondary battery, comprising mixing a lithium compound and a manganese compound, performing heat treatment in a temperature range of 900 to 1200 ° C., and annealing at 300 to 400 ° C. It is a method of manufacturing a material. In addition, a lithium compound and a manganese compound are mixed, and the mixture is heated at a temperature of 900 to 1200 ° C., and the obtained spinel-type cathode material for a lithium secondary battery is cooled to room temperature. In the method for producing a material, a cooling rate of 500 to 300 ° C. is set to 5 ° C./h.
This is a method for producing a spinel-type positive electrode material for a lithium secondary battery, characterized by being at most r. Further, the present invention is a spinel-type positive electrode material for a lithium secondary battery having a pH in the range of 6 to 9, which is obtained by the above manufacturing method. Further, there is provided a lithium secondary battery using the spinel-type positive electrode material for a lithium secondary battery described above.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, lithium carbonate (L
i2CO3), lithium nitrate (Li2NO3), lithium hydroxide (LiOH) and the like. Manganese raw materials include manganese dioxide (MnO2).

[0007] In order to obtain a larger reaction area, these raw materials are preferably ground before or after mixing the raw materials. The weighed and mixed raw materials may be used as they are or may be granulated and used. The granulation method may be wet or dry.

[0008] These raw materials are put into a firing furnace, and 900
Baking is performed in a temperature range of 1 to 1200 ° C. Examples of the firing furnace used here include a rotary kiln and a stationary furnace. The firing time is 1 hour or more, preferably 5 to 20 hours, to obtain a uniform reaction. The lithium manganate synthesized here is used as a positive electrode material for lithium secondary batteries of not only 4 V class but also 5 V class.

Here, with respect to the lithium secondary battery, the positive electrode material, a conductive material such as carbon black, and a binder such as Teflon (trade name: polytetrafluoroethylene) are mixed to form a positive electrode mixture, For the negative electrode, a material capable of desorbing and occluding lithium such as lithium alloy or carbon is used. As the non-aqueous electrolyte, a lithium salt such as lithium hexafluorophosphate (LiPF6) is used such as ethylene carbonate-dimethyl carbonate. Those dissolved in a mixed solvent or those obtained by converting them into a gel electrolyte are used.

[0010]

EXAMPLE 1 Lithium carbonate 24.1 based on 100 manganese dioxide
After mixing with a ball mill, the mixture was fired at 900 ° C. for 20 hours. Thereafter, the temperature was lowered to 500 ° C. at a rate of 30 ° C./hr, then allowed to cool to 350 ° C. in the air, and annealed at 350 ° C. for 7 hours.

The spinel-type cathode material 10 thus obtained
g in 50 cc of water for 10 minutes.
When H was measured, it was pH = 7.5. Further, the obtained spinel-type positive electrode material was mixed with acetylene black and Teflon binder to prepare a positive electrode mixture. 40 mg of this positive electrode mixture was weighed, formed into a disk having a diameter of 12 mm, dried at 200 ° C. under vacuum, and a model cell of a lithium secondary battery was prepared using a metal lithium counter electrode. After charging this to 4.3 V, the discharge capacity (initial capacity) up to 3.0 V was measured and found to be 105.2 mAh.
/ G. The battery was charged at 60 ° C for 3 hours.
When stored for days, the capacity retention after storage was 79%, which was superior to Comparative Example 1.

Example 2 100 parts of manganese dioxide and 24.1 parts of lithium carbonate
After mixing in a ball mill, the mixture was fired at 900 ° C. for 20 hours. Thereafter, the temperature is lowered to 500 ° C. at 30 ° C./hr,
The cooling rate was 3 ° C / hr between 500 and 300 ° C.

The spinel-type cathode material 10 thus obtained
g in 50 cc of water for 10 minutes.
When H was measured, it was pH = 7.3. Further, the spinel-type positive electrode material obtained here was mixed with acetylene black and Teflon binder to prepare a positive electrode mixture. 40 mg of this positive electrode mixture was weighed, formed into a disk having a diameter of 12 mm, dried at 200 ° C. under vacuum, and a model cell of a lithium secondary battery was prepared using a metal lithium counter electrode. After charging this to 4.3 V, the discharge capacity (initial capacity) up to 3.0 V was measured and found to be 105.1 mAh.
/ G. The battery was charged at 60 ° C for 3 hours.
After storage for days, the capacity retention after storage was 80%, which was superior to Comparative Example 1.

Example 3 Lithium carbonate was added to 100 parts of manganese dioxide.
After adding 1 and mixing with a ball mill, the mixture was fired at 900 ° C. for 20 hours. Thereafter, the temperature was lowered to 500 ° C. at a rate of 30 ° C./hr, and then allowed to cool to room temperature in the air. The spinel-type positive electrode material thus obtained was pulverized and mixed, and annealed again at 300 ° C. for 5 hours.

The spinel-type cathode material 10 thus obtained
g in 50 cc of water for 10 minutes.
When H was measured, it was pH = 6.7. Further, the obtained spinel-type positive electrode material was mixed with acetylene black and Teflon binder to prepare a positive electrode mixture. 40 mg of this positive electrode mixture was weighed, formed into a disk having a diameter of 12 mm, dried at 200 ° C. under vacuum, and a model cell of a lithium secondary battery was prepared using a metal lithium counter electrode. After charging the battery to 4.3 V, the discharge capacity (initial capacity) up to 3.0 V was measured to be 105.0 mAh.
/ G. The battery was charged at 60 ° C for 3 hours.
After storage for days, the capacity retention after storage was 82%, which was superior to Comparative Example 1.

Comparative Example 1 Lithium carbonate was added to 100 parts of manganese dioxide.
After adding 1 and mixing with a ball mill, the mixture was fired at 900 ° C. for 20 hours. Thereafter, the temperature was lowered to 500 ° C. at a rate of 30 ° C./hr, and then allowed to cool to room temperature in the air. 10 g of the spinel-type cathode material thus obtained was stirred in 50 cc of water for 10 minutes, filtered, and the pH was measured.
9.2. The battery characteristics were evaluated in the same manner as in Example 1, and the discharge capacity was 105.7 mAh / g. The capacity retention after storage was 75%.

[0017]

According to the present invention, a spinel-type positive electrode material for a lithium secondary battery having excellent high-temperature characteristics can be obtained at low cost.

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Claims (4)

[Claims] 1. A spinel-type positive electrode material for a lithium secondary battery, comprising mixing a lithium compound and a manganese compound, performing heat treatment in a temperature range of 900 to 1200 ° C., and annealing at 300 to 400 ° C. Manufacturing method. 2. A lithium secondary battery, wherein a lithium compound and a manganese compound are mixed and heat-treated in a temperature range of 900 to 1200 ° C., and the obtained spinel cathode material for a lithium secondary battery is cooled to room temperature. In the method for producing a spinel-type positive electrode material, a cooling rate of 500 to 300 ° C is set to 5 ° C /
hr or less, a method for producing a spinel-type positive electrode material for a lithium secondary battery. 3. The pH obtained by the production method according to claim 1 or 2,
Is a spinel-type positive electrode material for a lithium secondary battery in the range of 6 to 9. 4. A lithium secondary battery comprising the spinel-type positive electrode material for a lithium secondary battery according to claim 1.