Cathode active material for lithium secondary battery, process for preparing the same and reactor for use in the same process
The present invention relates to a cathode active material for a lithium secondary battery and a process for preparing the same. In accordance with the present invention, the cathode active material having a high packing density was designed and synthesized and thus provided is a cathode active material for a lithium secondary battery exhibiting structural stability such as improved characteristics for charge/discharge, service life and high-rate and thermal stability, by modifying surface of the electrode active material with amphoteric or basic compounds capable of neutralizing acid produced around the cathode active material.
1. A method for preparing a composite cathode active material for a lithium secondary battery, the method comprising:
producing a first lithium metal composite oxide by (a) precipitating a first metal composite hydroxide from a first mixture of a first metal precursor, a first aqueous ammonia solution and a first basic solution, and (b) mixing and reacting the first metal composite hydroxide with a first lithium precursor to form the first lithium metal composite oxide;
producing a second lithium metal composite oxide by (a) precipitating a second metal composite hydroxide from a second mixture of a second metal precursor, a second aqueous ammonia solution and a second basic solution, and (b) mixing and reacting the second metal composite hydroxide with a second lithium precursor to form the second lithium metal composite oxide; and
mixing the first and second lithium metal composite oxides in a ratio of 20:80 parts by weight, respectively, to form a composite cathode active material for a lithium secondary battery;
wherein
the first lithium metal composite oxide has a mean particle diameter that is greater than 60% but less than 90% of a mean particle diameter of the second lithium metal composite oxide;
the first and second lithium metal composite oxides comprise a primary particle having a particle diameter distribution between about 0.1 μm and about 0.2 μm, and a secondary particle having a mean particle diameter distribution between about 10 μm and about 20 μm when the primary particles are aggregated to form the secondary particles; and
the first lithium metal composite oxide has a formula
LiNi 1−x′−y CO x′ M′ y O 2 P z ;
the second lithium metal composite oxide has a formula selected from the group consisting of
Li 1+δ [Ni x Mn x−y/2 Co 1−2x−z M y N z ]O 2−a P a
and
Li 1+δ [Ni x Mn x+y Co 1−2(x+y) M y ]O 2−a P a ;
M is selected from the group consisting of Mg, Zn, Ca, Sr, Cu and Zr;
M′ is selected from the group consisting of Al, Mg, Zr and Ti;
N is selected from the group consisting of Fe, Al, Ga, In, Cr, Ge and Sn;
P is selected from the group consisting of F and S;
δ has a value such that -1/10≦δ≦1/10;
x has a value such that 0.2≦x≦0.4;
x′ has a value such that 0.1≦x′≦0.3;
y has a value such that 0≦y≦1/10;
z has a value such that 0≦z≦1/10; and
a has a value such that 0≦a≦0.3.
2. The method of claim 1 , wherein
the reactor includes an agitator having a first set of rotary vanes designed to induce fluid flow in a first direction and a second set of rotary vanes designed to induce fluid flow in a second direction that is reverse from the first direction; and
the reactor further includes a plurality of baffles that are spaced 2 to 3 cm apart from an inner wall of the reactor, have a shape of a flat panel and are attached to the inner wall by a plurality of connecting rods.