Cathode active material and lithium secondary battery comprising same
View Patent ↗Disclosed is a cathode active material for secondary batteries in which a carboxymethyl cellulose derivative is coated on surfaces of particles of a lithium transition metal oxide having the formula Li x M y O 2 where M: Ni a Mn b Co c wherein 0≦a≦0.9, 0≦b≦0.9, 0≦c≦0.5, and 0.85≦a+b+c≦1.05 and x+y=2, wherein 0.95≦x≦1.15.
1. A cathode mixture for secondary batteries, comprising:
a cathode active material and a binder,
wherein the cathode active material, in which a carboxymethyl cellulose derivative is coated on surfaces of particles of a lithium transition metal oxide represented by Formula 1 below:
Li x M y O 2 <Formula 1>
wherein M is Ni a Mn b Co c where 0≦a≦0.9, 0≦b≦0.9, 0≦c≦0.5, and 0.85≦a+b+c≦1.05); and
x+y=2, wherein 0.95≦x≦1.15,
wherein the carboxymethyl cellulose derivative is a material represented by Formula 2 below:
wherein at least one selected from the group consisting of R 1 , R 2 , and R 3 is CH 2 CO 2 X and the remaining group is CH 2 CO 2 H or OH, wherein X is Na; and
n is an integer of 1 or more and is determined within a range within which the carboxymethyl cellulose derivative has a weight average molecular weight (Mw) of 1,700,000 to 2,300,000,
wherein a rate to which R 1 , R 2 , and R 3 are CH 2 CO 2 X is 0.8 to 1.2,
wherein the binder is styrene-butadiene rubber,
wherein an amount of the binder is 1 wt % to 20 wt % based on a total weight of the cathode mixture, and
wherein a weight ratio of the carboxymethyl cellulose derivate:the styrene-butadiene rubber is 0.5:0.8 to 0.7:1.0.
2. The cathode mixture according to claim 1 , wherein, in Formula 1, amounts of Ni, Mn and Co satisfy the conditions: 0.2≦a≦0.7, 0<b≦0.5, and 0<c≦0.5.
3. The cathode mixture according to claim 1 , wherein M is substituted with at least one element selected from the group consisting of Al, Mg, Fe, Ti, V, Zr, Sn, and Zn.
4. The cathode mixture according to claim 1 , wherein a coating amount of the carboxymethyl cellulose derivative is in a range of 0.1 wt % to 10 wt % based on a total weight of the cathode active material.
5. The cathode mixture according to claim 1 , further comprising at least one material selected from the group consisting of a dispersion medium, a conductive material, a viscosity modifier, a filler, a coupling agent, and an adhesion promoter.
6. A cathode for secondary batteries, in which the cathode mixture according to claim 1 is coated on a current collector.
7. A lithium secondary battery comprising the cathode according to claim 6 .