Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Patent
1996-09-24
1998-09-15
Langel, Wayne
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
423593, C01G 4512
Patent
active
058075321
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of producing spinel type LiMn.sub.2 O.sub.4, and more particularly to a method of producing spinel type LiMn.sub.2 O.sub.4 usable for use in a cathode material for secondary lithium battery, a matrix for lithium adsorbent or the like.
BACKGROUND ART
As a starting material for LiMn.sub.2 O.sub.4, there is used a manganese compound being rich in source and cheap in the cost. Therefore, LiMn.sub.2 O.sub.4 is lately watched as an alternative material of LiCoO.sub.2 being a cathode material for high-voltage and high-energy density type secondary lithium battery.
In general, it is known that a specific surface area of the cathode material for the secondary lithium battery is an important factor determining a discharge capacity of the secondary lithium battery. That is, as the specific surface area of the cathode material becomes large, the reaction area of the battery becomes larger, so that it is said that the movement of ion is smooth and hence the decrease of capacity to the charge and discharge under heavy load is less.
Now, when LiMn.sub.2 O.sub.4 of amorphous strain spinel structure synthesized by firing at a low temperature is used as a cathode material for the secondary lithium battery, the discharge capacity is small though the specific surface area is large.
Therefore, it is desirable to use LiMn.sub.2 O.sub.4 having a large specific surface area and a crystalline spinel structure as the cathode material for high-voltage and high-energy density type secondary lithium battery.
Heretofore, crystalline spinel type LiMn.sub.2 O.sub.4 has been synthesized by dry-mixing lithium salt and manganese salt, for example, lithium carbonate and manganese oxide (Mn.sub.2 O.sub.3) or lithium carbonate and manganese carbonate at an atomic ratio of 1:2 and then firing the resulting mixed powder in an oxidizing atmosphere.
In the conventional process of producing LiMn.sub.2 O.sub.4, however, there are the following drawbacks:
1. Mn.sub.2 O.sub.3 is produced as an intermediate. This Mn.sub.2 O.sub.3 reacts with lithium carbonate to synthesize LiMn.sub.2 O.sub.4 of spinel structure. Therefore, the sintering of Mn.sub.2 O.sub.3 proceeds before the synthesis of LiMn.sub.2 O.sub.4 and hence the specific surface area of LiMn.sub.2 O.sub.4 lowers.
2. The starting powder is usually large in the particle size. Therefore, BET specific surface area of LiMn.sub.2 O.sub.4 after the firing is as very small as not more than 1 m.sup.2 /g.
3. The above dry-mixing is solid-solid mixing, so that microscopically uniform mixing is impossible at atomic or molecular level. Therefore, LiMn.sub.2 O.sub.4 obtained by firing through solid phase reaction becomes unstable in the crystal structure and is apt to cause defects.
Therefore, it is actual that materials having sufficient charge and discharge cycle property are not obtained by the above conventional method.
On the other hand, there is proposed a technique that the sintering promotion of Mn.sub.2 O.sub.3 (intermediate) resulting in the lowering of specific surface area is controlled by two-stage heat treatment of synthesizing LiMn.sub.2 O.sub.4 of amorphous strain spinel structure through low-temperature firing (not higher than 450.degree. C.) and then subjecting to reheating (600.degree.-700.degree. C.) to attempt the improvement in the specific surface area of
According to such a conventional technique, the specific surface area of LiMn.sub.2 O.sub.4 is improved. However, the method of producing LiMn.sub.2 O.sub.4 according to the conventional technique is a dry treatment, so that it has drawbacks that the crystal structure of LiMn.sub.2 O.sub.4 becomes unstable and the defects are liable to be caused. Therefore, it can not be expected that materials having sufficient charge and discharge cycle property are obtained by this method.
It is an object of the present invention to solve the above drawbacks and to establish a technique of stably producing a crystalline spinel type LiMn.sub.2 O.sub.4 having a large specific surface area by mic
REFERENCES:
patent: 2562705 (1951-07-01), Ellestad et al.
patent: 4567031 (1986-01-01), Riley
patent: 5370948 (1994-12-01), Hasegawa et al.
patent: 5567401 (1996-10-01), Doddapaneni et al.
English langauge abstract of JP No. 2-9722.
English langauge abstract of JP No. 6-275276.
Satoh Keiji
Sotomura Takeshi
Takahashi Koh
Japan Metals and Chemicals Co., Ltd.
Langel Wayne
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