COMPARATIVE-STUDY OF LICOO2, LINI1/2CO1/2O2 AND LINIO2 FOR 4-VOLT SECONDARY LITHIUM CELLS

The preparation and characterization of LiNi1-xCoxO2 compounds (0 less-than-or-equal-to x less-than-or-equal-to 1) having a space group R3mBAR, for 4 volt secondary lithium cells were investigated. By developing processing methods, homogeneous LiNi1-xCoxO2 samples were obtained and characterized by XRD, ir and magnetic susceptibility measurements. When increasing x in LiNi1-xCoxO2, the unit cell dimensions a and c in hexagonal setting, decreased almost linearly as a function of x. Magnetic susceptibility measurements indicated that LiNi1-xCoxO2 consists of low-spin states of Co3+ (t2g6 eg0) and Ni3+ (t2g6 e(g)1). All samples may be used as positive electrodes in nonaqueous lithium cells. Of these, LiCoO2 showed the highest working voltage and about l20 mAh g-1 of rechargeable capacity, and LiNi1/2Co1/2O2 showed the lowest working voltage and about 130 mAh g-1 of rechargeable capacity in the voltage range 2.5-4.2 V in 1 M LiClO4 propylene carbonate solution. LiNiO2 has more than 150 mAh g-1 of rechargeable capacity with working voltages above 3.5 V. Secondary lithium ion cells which consisted of LiNi1-xCoxO2 cathodes and natural graphite anodes, were also examined and the specific problems of establishing an innovative secondary lithium cell were discussed.