Positive electrode active material for lithium secondary battery and process for producing the same

Abstract

A positive electrode active material for a lithium secondary battery containing a lithium-cobalt composite oxide, which has a large volume capacity density, has a high safety and is excellent in charge and discharge cyclic durability, and its production process, are provided. A lithium-cobalt composite oxide represented by the formula LipCoxMyOzFa (wherein M is a transition metal element other than Co or an alkaline earth metal element, 0.9≦p≦1.1, 0.980≦x≦1.000, 0≦y≦0.02, 1.9≦z≦2.1, x+y=1 and 0≦a≦0.02) and comprising a mixture containing substantially spherical hard first particles of lithium-cobalt composite oxide having such a sharp particle size distribution that the volume basis cumulative size D10 is at least 50% of the average particle size D50, and the volume basis cumulative size D90 is at most 150% of the average particle size D50, and second particles of lithium-cobalt composite oxide filling the space among the first particles, in a mass ratio of first particles / second particles of from 1 / 2 to 9 / 1, and process for producing the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode active material for a lithium secondary battery, which has a large volume capacity density and high safety and is excellent in the charge and discharge cyclic durability, a positive electrode for a lithium secondary battery employing it, and a lithium secondary battery. BACKGROUND ART [0002] Recently, as the portability and cordless tendency of instruments have progressed, a demand for a non-aqueous electrolyte secondary battery such as a lithium secondary battery which is small in size and light in weight and has a high energy density, has been increasingly high. As a positive electrode active material for the non-aqueous electrolyte secondary battery, a composite oxide of lithium and a transition metal such as LiCoO2, LiNiO2, LiNi0.8Co0.2O2, LiMn2O4 or LiMnO2, has been known. [0003] Among them, a lithium secondary battery using a lithium-cobalt composite oxide (LiCoO2) as a positive electrode active mater...

AI Technical Summary

Benefits of technology

[0010] It is an object of the present invention to provide a positive electrode active material for a lithium secondary battery, which has a large volume capacity density and high safety and is excellent in the charge and discharge cyclic durability, a positive electrode for a lithium secondary battery employing it, and a lithium secondary battery.

[0011] The present inventors have continued extensive studies to achieve the above object and as a result, have found that a positive electrode active material containing a lithium-cobalt composite oxide having a specific composition and comprising a mixture containing first particles of lithium-cobalt composite oxide being hard and substantially spherical and having such a sharp particle size distribution that the volume basis cumulative size D10 is at least 50% of the average particle size D50 and the volume basis cumulative size D90 is at most 150% of the average particle size D50, and second particles of lithium-cobalt composite oxide filling the space among the first particles, in a specific proportion of the first particles and the second particles, has a compacted dense structure and thereby has large volume capacity density and press density, and the above object can be achieved by the positive electrode active material.

Problems solved by technology

On the other hand, there has been a problem of deterioration of the cyclic properties such as gradual reduction of the battery discharge capacity due to repetitive charge and discharge cycle, a problem of the weight capacity density or substantial reduction of the discharge capacity at a low temperature.

With such a positive electrode active material, the coating properties and the cyclic properties have been improved, but, the safety, the volume capacity density and the weight capacity density, have not yet been fully satisfactory.

In such a proposal, there may be a case where the weight capacity density and the charge and discharge cyclic properties of the positive electrode can be improved, but on the other hand, there is a complication that the positive electrode material powders having two types of particle size distributions have to be produced, and one satisfying all of the volume capacity density, the safety, the coating uniformity, the weight capacity density and the cyclic properties of the positive electrode, has not yet been obtained.

However, in the prior art, there has been no lithium secondary battery using a lithium-cobalt composite oxide as a positive electrode active material, which sufficiently satisfies all of the volume capacity density, the safety, the coating uniformity, the cyclic properties and further the low temperature properties.