Characteristics of LiCoO_2, LiMn_2O_4 and LiNi_(0.45)Co_(0.1)Mn_(0.45)O_2 as cathodes of lithium ion batteries

摘要

LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2 was synthesized from Li_2CO_3 and a triple oxide of nickel, cobalt and manganese at 950℃ in air. The structures and characteristics of LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2, LiCoO_2 and LiMn_2O_4 were investigated by XRD, SEM and electrochemical measurements. The results show that LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2 has a layered structure with hexagonal lattice. The commercial LiCoO_2 has sphere-like appearance and smooth surfaces, while the LiMn_2O_4 and LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2 consist of cornered and uneven particles. LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2 has a large discharge capacity of 140. 9 mA · h/g in practical lithium ion battery, which is 33.4% and 2.8% above that of LiMn_2O_4 and LiCoO_2, respectively. LiCoO_2 and LiMn_2O_4 have higher discharge voltage and better rate-capability than LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2. All the three cathodes have excellent cycling performance with capacity retention of above 89.3% at the 250th cycle. Batteries with LiMn_2O_4 or LiNi_(0.45)Co_(0.10)Mn_(0.45)O_2 cathodes show better safety performance under abusive conditions than those with LiCoO_2 cathodes.