Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-09-17
2004-03-02
Ryan, Patrick (Department: 1745)
Metal working
Method of mechanical manufacture
Electrical device making
C429S224000
Reexamination Certificate
active
06699297
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing lithium manganate with a spinel structure which is suitable for an electrode material of a lithium ion secondary battery, to lithium manganate obtained by the process, to the positive electrode for a lithium ion secondary battery employing the same and to a lithium ion secondary battery.
BACKGROUND ART
With recent advances in electronics technology, the downsizing of electronic devices such as personal computers and cellular phones is progressing at an accelerating pace. This has also led to downsizing of power sources, and thus to a recent increase in the development of lithium secondary batteries. From an environmental standpoint, electric automobiles have attracted attention and some have been put into practical use. Widespread use of such electric automobiles will require batteries with large capacities and excellent cycle characteristics as power sources, and the use of lithium ion secondary batteries for such large-sized batteries is therefore examined.
As concerns the positive electrode active materials for lithium batteries, manganese dioxide has been used for primary batteries and vanadium oxide or lithium and cobalt compounds have been used for secondary batteries. Lithium manganate oxides such as lithium manganate are being actively developed because of the inexpensiveness and absence of toxicity of their starting materials, which are manganese compounds, compared to cobalt compounds.
Among various lithium manganates, lithium manganates with a spinel structure, owing to their three-dimensional configuration, allow stable doping and undoping of lithium ions into crystal lattices without destruction of the crystal structure when used as positive electrode materials for lithium ion secondary batteries undergoing charge and discharge. Also, their high discharge voltage and stability make them very promising as positive electrode active materials for secondary batteries, such that much research has been directed in recent years toward rendering them practical for use. However, their theoretical capacity is as low as 148 mAh/g, and their charge/discharge cycle characteristics are poor. An important goal has therefore been to synthesis spinel-type lithium manganate of very high purity with the lithium and manganese evenly dispersed.
One of the preferred characteristics required of lithium manganate with a spinel structure used as a positive electrode substance for lithium ion secondary batteries is a maximized electrode surface, in cases with liquid conductive electrolytes, and specifically, it is preferred to have a high specific surface area, low crystallinity (low density), high pore volume and a high manganate number.
In the case of solid electrolytes, however, permeation through pores does not occur and therefore gaps are detrimental. In this case, then, the preferred characteristics required for the lithium manganate are a high specific surface area, high density, low pore volume and minimal granularity.
Conventionally, lithium manganate with a spinel structure is obtained from a lithium compound such as lithium hydroxide, lithium nitrate, lithium oxide, lithium carbonate or lithium acetate and a manganese compound such as manganese oxide, manganese carbonate or &ggr;-MnOOH, as the starting materials, and is produced by solid phase reaction, solid phase sintering, melt impregnation, a hydrothermal method, electrodeposition or chelating.
However, since solid phase methods and solid phase sintering methods are carried out at high temperature, sintering occurs which reduces the specific surface area. It is therefore impossible to achieve charge and discharge with a high current density. In other words, because solid phase reaction is a batch reaction, such reactions are slow and non-uniform, and the resulting lithium manganate compounds have also had a non-uniform composition. Furthermore, because of the largeness of the particles obtained thereby, they are unsuitable as electrode materials and have exhibited particular deterioration in charge/discharge cycle characteristics. Solid phase reaction, which is a diffusion reaction, also requires the particles of the starting solids to be on the submicron level in order to accomplish a homogeneous reaction. However, manganese compounds and lithium compounds are usually large particles on the order of a few microns to several tens of microns, while lithium hydroxide particles are usually 100 microns or larger, such that it has been difficult to obtain a uniform mixture and homogeneous reaction has not been possible.
Synthesis by hydrothermal methods is carried out at a high temperature of 100 to 300° C. and under a high pressure of 300 atmospheres, and using a reaction apparatus which must be able to withstand these conditions increases energy costs and equipment costs. With melt impregnation, pulverization is necessary to obtain a highly porous manganese starting material, and pulverization can result in inclusion of impurities such as iron, thus posing a problem in terms of product purity.
For synthesis of more homogeneous lithium manganate, it has been attempted to synthesize lithium manganate with a spinel structure by liquid phase reaction. For example, in Japanese Unexamined Patent Publication No. HEI 2-183963 there is disclosed a process in which a divalent manganese salt and a lithium salt are reacted in an alkali aqueous solution to obtain a lithium-containing manganese hydroxide compound, and then the manganese hydroxide compound is oxidation treated, washed and heat treated at 800 to 900° C. to produce manganese oxide with a spinel structure. However, this process reduces the lithium component by the washing after oxidation treatment, such that the lithium content of the resulting product is lowered, and it is difficult to obtain lithium manganate having the desired Li/Mn molar ratio. Although it is a liquid phase reaction, the lithium manganate must be obtained by heat treatment after the manganese hydroxide compound has been produced by the liquid phase reaction.
Thus, the related art has not been able to achieve lithium manganate with a spinel structure that is useful as a positive electrode active material for a lithium ion secondary battery, nor has any inexpensive or convenient synthesis method existed.
On the other hand, a lithium ion secondary battery utilizing lithium manganate is disclosed in Japanese Unexamined Patent Publication No. HEI 1-109662 as a nonaqueous secondary battery with a lithium manganate compound represented by LiMn
2
O
4
with a spinel structure as the positive electrode active material and a lithium alloy as the negative electrode active material, and employing a lithium ion-containing nonaqueous electrolyte. In Japanese Unexamined Patent Publication No. HEI 10-50316 there is disclosed an organic electrolyte secondary battery comprising a lithium-containing negative electrode and comprising as the positive electrode active material a LiMn
2
O
4
compound synthesized from lithium carbonate and manganese dioxide.
The related art for such lithium ion secondary batteries employing lithium manganate as the positive electrode active material has improved charge/discharge capacity and cycle characteristics over the previously used batteries employing manganese oxide or chalcogenides of titanium, molybdenum or niobium as the positive electrode active material.
Nevertheless, with the increasing demands for even higher voltages and higher energy from secondary batteries in recent years, there has been a demand for secondary batteries with even larger charge/discharge capacities and more excellent charge/discharge cycle characteristics, and these demands have still not been satisfied by the related art and called for further improvement.
It is therefore an object of the present invention to provide a novel, inexpensive and convenient process for production of lithium manganate with a spinel structure that is useful as an electrode material, and especially a positive electrode active material, for a lithium ion secondary bat
Sakai Hideki
Yamawaki Tetsuya
Dove Tracy
Ryan Patrick
Toho Titanium Co., Ltd.
Westerman Hattori Daniels & Adrian LLP
LandOfFree
Method for preparing lithium manganate and positive... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing lithium manganate and positive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing lithium manganate and positive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3256769