  At present, the most common type of cathode materials, NCA
[Li_(1-x)Ni_(0.80)Co_(0.15)Al_(0.05)O_(2), x = 0 to 1], have a very high
concentration of cobalt. Since cobalt is toxic and expensive, the existing
design of cathode materials is neither cost-effective nor environmentally
benign. We have performed density functional theory (DFT) calculations to
investigate electrochemical, electronic, and structural properties of four
types of NCA cathode materials with the simultaneous decrease in Co content
along with the increase in Ni content. Our results show that even if the cobalt
concentration is significantly decreased from 16.70 % (NCA_I) to 4.20 %
(NCA_IV), variation in intercalation potential and specific capacity is not
significant. For example, in case of 50% Li concentration, the voltage drop is
only ~17% while the change in specific capacity is negligible. Moreover, we
have also explored the influence of sodium doping in the intercalation site on
the electrochemical, electronic, and structural properties. By considering two
extreme cases of NCAs (i.e., with highest and lowest Co content: NCA_I and
NCA_IV respectively), we have demonstrated the importance of Na doping from the
structural and electronic point of view. Our results provide insight into the
design of environmentally benign, low-cost cathode materials with reduced
cobalt concentration.
