Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1997-08-13
2001-02-13
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S223000, C429S231950
Reexamination Certificate
active
06187282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to a method of manufacturing a lithium complex oxide, especially a lithium cobalt complex oxide or a lithium nickel complex oxide, both of which are useful as, for example, a cathode active material of a secondary lithium battery.
2. Related Art of the Invention
As methods of manufacturing a lithium cobalt complex oxide or a lithium nickel complex oxide which are used as an cathode active material of a secondary lithium battery, the following methods have been proposed so far.
Lithium Cobalt Complex Oxide:
(a) A powder method in which, say, powders of lithium carbonate and cobalt oxide are mixed, and then fired at about 850° C.
(b) A spray-pyrolysis method in which lithium nitrate and cobalt nitrate are dissolved in water, and the solution is ultrasonically atomized for pyrolysis.
Lithium Nickel Complex Oxide:
(c) A solid-phase (powder) method in which powders of, say, lithium carbonate and nickel oxide are mixed, and then fired at about 750° C. in an oxygen gas stream.
(d) A method in which lithium nitrate or hydroxide and nickel hydroxide, each of which has low-melting point, are mixed with each other, and then fired at a low temperature in an oxygen gas stream.
(e) A spray-pyrolysis method in which lithium nitrate and nickel nitrate are dissolved in water, and their solution is ultrasonically atomized for pyrolysis.
However, the above methods involved the following problems.
The powders of carbonates and oxides used as the starting materials in the powder method (a) require firing at a relatively high temperature. As a result, heavy vaporization of lithium occurs, and there is obtained a product having a Li/Co molar ratio deviating from the desired range. It is impossible to mix the powders uniformly on a molecular basis, resulting, for example, in the formation of Co
2
O
3
in addition to the LiCoO
2
desired, and in order to avoid this, it has been necessary to repeat extended time firing several times. The spray-pyrolysis method (b) makes it possible to mix elements forming a lithium cobalt complex oxide uniformly on an ionic basis and realize a drastically improved level of uniformity, as compared with the solid-phase method. It has also the advantage that, as it does not necessitate any step for crushing the raw materials, it can avoid the inclusion of impurities that would result from any crushing step.
However, a series of the steps in this spray-pyrolysis method including vaporization of the solvent and pyrolysis are conducted within short period of time, and the complex oxide which is thereby synthesized tends to be of low crystallinity since it has a very short heat history as compared with the product of conventional firing treatment. If it is used as an active material for a secondary battery, the repeated charging and discharging of the battery results in a broken crystal structure of the material and a lower battery capacity. Moreover, the complex oxide has a very large specific surface area on the order of several tens of square meters per gram, and the decomposition of an electrolyte contacting it brings about a serious lowering in the cycle life of the secondary battery and its storage stability.
The powders of carbonates and oxides used as the starting materials in the powder method (c) require firing at a relatively high temperature. As a result, like the method (a), vaporization of lithium occurs heavily, and there is obtained a product having a Li/Ni molar ratio deviating from the desired range. It is impossible to mix the powders uniformly on a molecular basis, resulting, for example, in the formation of Li
2
Ni
8
O
10
in addition to LiNiO
2
as desired, and in order to avoid this, it has been necessary to repeat extended time firing several times.
The method (d) gives a small deviation from the desired Li/Ni ratio, as compared with the solid-phase method, since it employs a lower temperature for synthesis. However, there is obtained a complex oxide of low crystallinity unless a long firing time is employed. If it is used as an active material for a secondary battery, the repeated charging and discharging of the battery results in a broken crystal structure of the material and a lower battery capacity. In the event that cations having a radius close to Ni ions, such as Fe, Co, Mn, Mg or Al, have been substituted for Ni in order to make a secondary battery having an improved cycle life to withstand repeated charging and discharging, it has been impossible to avoid a lack of uniformity in the distribution of Ni and substituted cations.
The spray-pyrolysis method (e) makes it possible to mix elements forming a complex oxide of lithium and nickel uniformly on an ionic basis, and realize a drastically improved level of uniformity, as compared with the other methods. It has also the advantage that, like the method (b), as it does not necessitate any step for crushing the raw materials, it can avoid the inclusion of impurities that would result from any crushing step. However, this spray-pyrolysis method has same problems as method (b) described before.
It is, therefore, an object of this invention to solve the above problems and provide a manufacturing method of a lithium complex oxide comprising cobalt or nickel which is homogeneous, and enables a long cycle life to withstand repeated charging and discharging and a high level of storage stability when used as an cathode active material of a secondary lithium battery.
SUMMARY OF THE INVENTION
The invention provides a manufacturing method of a lithium complex oxide comprising the steps of 1) atomizing and pyrolyzing an aqueous or alcohol solution of compounds containing metallic salts constituting a lithium cobalt complex oxide or a lithium nickel complex oxide, and 2) annealing said lithium cobalt complex oxide or said lithium nickel complex oxide to increase the average particle diameter thereof to between about 1 and 5 micrometers and adjust the specific surface area thereof to between about 2 and 10
2
/g.
In the above manufacturing method of a lithium complex oxide, the atomizing and pyrolyzing temperature is preferably between about 500 and 900° C., and more preferably about 600-800° C.
In the above manufacturing method of a lithium complex oxide, the annealing temperature is preferably between about 500 and 850° C., and more preferably about 600-800° C.
In the above manufacturing method of a lithium complex oxide, said lithium complex oxide may be LiCoO
2
.
In the above manufacturing method of a lithium complex oxide, said lithium complex oxide may be LiNiO
2
.
In the above manufacturing method of a lithium complex oxide, said compounds containing metallic salts may be inorganic acid salts.
The metallic salts may comprise a combination of at least one selected from the group of lithium nitrate, lithium acetate and lithium formate and at least one selected from the group of cobalt nitrate, cobalt acetate and cobalt formate.
If the aqueous and/or alcoholic solution of compounds containing metal elements for forming a lithium cobalt
ickel complex oxide is sprayed in a heated atmosphere, as stated above, it undergoes pyrolysis instantaneously and is finely divided by its own chemical decomposition to form a finely divided complex oxide of high surface activity. Then, the complex oxide is annealed to produce a complex oxide of high surface activity having a particle diameter of about 1-5 micrometers and a specific surface area of about 2-10 m
2
/g which is suitable as an cathode active material of a secondary lithium battery.
The lithium cobalt complex oxide and the lithium nickel complex oxide according to this invention are not limited to LiCoO
2
and LiNiO
2
, respectively. The lithium cobalt
ickel complex oxide also includes any product obtained by substituting, for example, Cr, Mn, Fe, Ni/Co, Mg or Al for a part of Co/Ni to realize improved properties. Thus, the metal elements forming a lithium cobalt
ickel complex oxide according to this invention are not only Li and Co/Ni, but also include Cr, Mn, Fe, Ni/Co, Mg
Hattori Koji
Sakabe Yukio
Yamashita Yasuhisa
Dunn Tom
Murata Manufacturing Co. Ltd.
Nguyen Cam N.
Ostrolenk Faber Gerb & Soffen, LLP
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