This invention relates to the improvement of lithium-manganese oxides, more particularly to a lithium-manganese complex oxide having a spinel crystalline structure, which is represented by a formula Li[Mn2-X-YLiXMY]O4+xcex4 (wherein M is at least one element selected from the groups IIa, IIIb and VIII of the 3rd and 4th periods, and 0.02xe2x89xa6Xxe2x89xa60.10, 0.05xe2x89xa6Yxe2x89xa60.30 and xe2x88x920.2xe2x89xa6xcex4 less than 0.2), wherein average diameter of crystal grains by scanning electron microscopic (SEM) observation is 2 xcexcm or less and half value width of the (400) plane of powder X-ray diffraction by CuKxcex1 is 0.22xc2x0 or less, and a lithium-manganese complex oxide having a spinel crystalline structure, wherein its BET specific surface area is 1.0 m2xc2x7gxe2x88x921 or less, and also to an Mn-M complex oxide slurry material which renders their production possible, a production method thereof and a lithium secondary battery which uses the lithium-manganese complex oxide as the positive electrode active material.
Since lithium secondary batteries have high energy density, their application to a broad range of fields is in progress as new type secondary batteries of the next generation, and studies on them, including those which were already put into practical use, are in progress with the aim of obtaining more higher performance.
Manganese-based materials are one of the promising materials, because the material manganese is abundant and inexpensive in view of resources and gentle with the environment.
With the popularization of mobile machinery, great concern has been directed toward a small-sized, light weight and high energy density lithium secondary battery, and lithium ion batteries in which a carbonaceous material capable of charging and discharging lithium was used in the negative electrode have been put into practical use.
Though lithium-cobalt oxide (to be referred to as LiCoO2 hereinafter) is mainly used in the positive electrode material of the current lithium ion batteries, cobalt materials are expensive so that development of its substitute material is expected.
Lithium-nickel oxide (to be referred to as LiNiO2 hereinafter) and lithium-manganese spinel (to be referred to as LiMn2O4 hereinafter) can be exemplified as the positive electrode material which can be substituted for LiCoO2 and show a 4 V-class electromotive force, but LiMn2O4 is considered to be the most excellent positive electrode material for hybrid type electric car batteries and fuel cell auxiliary power supply, because it is abundant and inexpensive in view of resources, has low influence on the environment and can easily ensure safety when made into a battery, and vigorous research and development are being carried out with the aim of its practical use.
However, it has been pointed out that LiMn2O4 has a problem regarding high temperature stability, namely capacity reduction and preservation characteristics by charging and discharging at a high temperature, so that concern has been directed toward the resolution of this problem.
For example, LiXMn(2-Y)AlYMYO4 in which Al was doped to LiMn2O4 (Japanese Patent Laid-Open No. 289662/1992) and Li[Mn2-X-YLiXMeY]O4 wherein Me represents a metal (Japanese Patent Laid-Open No. 7956/1999) have been proposed, but their capacity maintaining ratio after 50 cycles of charge and discharge is 96% to the maximum, thus still leaving a room to be improved.
The object of the invention is to propose a lithium-manganese complex oxide having improved high temperature stability and a production method thereof and to provide a high output lithium secondary battery which uses this compound as the positive electrode active material.
As a result of intensive studies carried out with the aim of improving high temperature stability of LiMn2O4, namely charge and discharge cycle characteristics and preservation characteristics at a high temperature, it was found that a spinel crystalline structure lithium-manganese complex oxide represented by a formula Li[Mn2-X-YLiXMY]O4+xcex4 (wherein M is at least one element selected from the groups IIa, IIIb and VIII of the 3rd and 4th periods, and 0.02xe2x89xa6Xxe2x89xa60.10, 0.05xe2x89xa6Yxe2x89xa60.30 and xe2x88x920.2xe2x89xa6xcex4xe2x89xa60.2), having a half value width of the (400) plane of powder X-ray diffraction by CuKxcex1 of 0.22xc2x0 or less and an average diameter of crystal grains by SEM observation of 2 xcexcm or less, and a spinel crystalline structure lithium-manganese complex oxide having a BET specific surface area of 1.0 m2xc2x7gxe2x88x921 or less, can be synthesized by producing in advance an Mn-M complex oxide slurry material by adding an alkali to a metal salt aqueous solution of M (M is at least one element selected from the groups IIa, IIIb and VIII of the 3rd and 4th periods) containing electrolytic manganese dioxide as the manganese material, while stirring the solution, then adding a lithium material thereto and baking the mixture in the air or in an atmosphere of high concentration oxygen (including pure oxygen atmosphere), namely in an atmosphere of from 18 to 100% oxygen concentration, and that a manganese-based lithium secondary battery having sharply improved high temperature stability, which can not be achieved with the conventional materials, can be constructed by the use of the compound as the positive electrode active material, thereby resulting in the accomplishment of the invention.