Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-02-20
2004-11-02
Le, Hoa Van (Department: 1752)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S218100, C429S223000, C429S224000, C429S231100, C429S231300
Reexamination Certificate
active
06811923
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a positive electrode active material for secondary batteries and a manufacturing method thereof and a nonaqueous electrolytic solution secondary battery, and reproduced electronic functional material and a reproduction method of electronic functional material.
RELATED ART
Recently, portable electronic devices, such as note type personal computers, personal digital assistants (PDAs), cellular phones, video cameras and so on, are rapidly spreading. As they spread, for secondary batteries for use in the portable electronic devices, there are strong demands for smaller size, higher capacity, higher cycle life and so on.
As a secondary battery capable of satisfying such demands, there is known a Li ion secondary battery that utilizes a nonaqueous electrolytic solution including, for instance, a Li salt. In the Li-ion secondary battery, a Li containing transition metal composite oxide, such as LiCoO
2
, LiNiO
2
, or LiMn
2
O
4
, is used as the positive electrode active material. For a negative electrode, carbonaceous material is utilized, and a nonaqueous electrolytic solution, in which a lithium salt, such as LiPF
6
or LiBF
4
, is dissolved in a nonaqueous solvent, is utilized.
The Li ion secondary battery has advantages, in comparison with a secondary battery that uses lithium metal, in that safety thereof is remarkably excellent; a voltage a unit cell is high; and a high energy density may be obtained. From these circumstances, the lithium ion secondary batteries are in heavy usage as a power source of the portable electronic device.
The positive electrode active material, such as LiCoO
2
or LiNiO
2
, is normally obtained by sintering a mixture of cobalt oxide or nickel oxide and lithium carbonate in air at a temperature of substantially 900° C. to convert into a composite oxide. The composite oxide obtained through the sintering is milled to a particle diameter of substantially from several micrometers to several tens micrometers, followed by suspending, together with a conductive material and a binder, in an appropriate solvent, thereby slurry is prepared. The slurry is coated on a current collector (metal foil), followed by drying, thereby forming in plate. Thus, a positive electrode is prepared.
However, the lithium ion secondary battery, which uses the existing positive electrode as mentioned above, has a problem in that a voltage drop tends to occur at initial charge, thereby causing a decrease in manufacturing yield and a deterioration of battery performance. Furthermore, as to the decrease in the manufacturing yield, clogging when the positive electrode slurry is coated on the collector and destruction of the collector (metal foil) are also decrease-causing factors.
We studied the aforementioned phenomena and found that powdery metal impurities and agglomerated particles mingled in many cases in the positive electrode active material, which was prepared according to the existing manufacturing method, and these caused problems. Since particles of the metal impurity and the agglomerated particles are only slightly mingled, it is considered that these were overlooked in the existing manufacturing process. Furthermore, sieving is generally used in removing the powdery impurities, but cannot effectively remove particles of the metal impurity and the agglomerated particles, which are small in the difference of particle size from that of particles of original active material.
From these circumstances, in the positive electrode active material for secondary batteries, it is strongly demanded to remove battery performance- and manufacturing yield-deteriorating factors. Furthermore, the impurity particles and agglomerated particles cause problems not only in the ordinary positive electrode active material for secondary batteries, but also in the positive electrode active material, which is physically recovered from waste electrodes and reproduced.
That is, in relation to recent problems of resource starvation and environmental contamination, demands for reproduction of electric appliances are stronger than ever. In electronic functional materials for use in various kinds of electric appliances, in general, expensive metal materials are used. Accordingly, so far, necessity of recovery has been discussed, and recovery and reuse have been actually tried.
In a manufacturing process of secondary batteries, such as lithium ion batteries, due to condition adjustment and cutting into a specified size, there occurs a large amount of waste electrodes, to which the positive electrode active material sticks. From such waste electrodes, Co is recovered and refined by melting; it is once returned to raw material Co
3
O
4
or the like; thereafter, the positive electrode active material is reproduced by synthesizing again LiCoO
2
or the like.
The aforementioned method is called a chemical reproduction because the recovered waste material is chemically returned to raw material before synthesis. In this method, since the electronic functional material being reused has to be re-synthesized from raw material, there is a problem in that reproducing costs are high. Meanwhile, it has been studied to reproduce the electronic functional material without performing separation of the raw material and re-synthesis.
As to the waste electrodes of the secondary batteries, a method for directly recovering the active material, such as LiCoO
2
or the like, is proposed (Japanese Laid-Open Patent Application No. 10-8150 JP-A). Specifically, an Al foil (waste electrode), on which the positive electrode material is coated, is heat-treated at a temperature where Al is not melted and LiCoO
2
is not decomposed. Thereby, the positive electrode material is separated from the Al foil, and the conductive material and binder are decomposed and removed. Thereby, the positive electrode active material, such as LiCoO
2
or the like, may be directly recovered.
In order to discriminate such recovery, reproduction method from the chemical reproduction, which chemically converts to the raw material before the synthesis and recovers, this method is called here a physical reproduction method. The physical reproduction method has advantages over the chemical reproduction method in that processing costs for reproducing the electronic functional material are lower; it is very advantageous from a practical point of view.
As a general physical reproduction process, first, powdery, slurry-like, coating-like electronic functional materials, which are target objects, are recovered from various kinds of electronic components and waste materials of the electronic appliances. When the electronic functional material being reproduced is coating-like, it is peeled from a substrate or the like. Then, large foreign material, such as the substrate, from which the electronic functional material has been peeled off, is separated and removed, further followed by removing the foreign material or impurities, which are capable of removing by washing. As needs arise, heat-treatment, acid- or alkali-treatment is applied to remove removable foreign material and impurities. Furthermore, by applying sieving or drying, without performing the synthesis, reproduced powdery electronic functional material is obtained.
In the physical reproduction, it is necessary that characteristics of the electronic functional material is not deteriorated, even after the various kinds of treatment processes are applied. However, there are problems in that due to mingling of the foreign material, which is actually difficult to separate, fine powder caused by brittleness due to heat in the peeling- or heat-treatment process, mingling of large agglomerations due to residuals of the binder component, characteristics of the reproduced electronic functional material deteriorate. In the physical reproduction of the positive electrode active material for secondary batteries, there is a large possibility of mingling of the impurities, which are difficult to separate by means of the sieving or the like, and furthermore there are a lot of
Iyasu Kotaro
Mitsui Hisayasu
Sakai Ryo
Shirakawa Yasuhiro
Suzuki Nobukazu
Kabushiki Kaisha Toshiba
Le Hoa Van
Shanks Mark R.
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