Low Temperature Electrochemical Properties of Li[Ni_xCo_yMn_1-x-y]O₂Cathode Materials for Lithium-Ion Batteries

The electrochemical performances of Li[Ni x Co y Mn 1-x-y ]O 2 (x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) synthesized via a co-precipitation method are investigated at low temperatures (0 ∼ −20°C). The resulting electrochemical properties of Li[Ni x Co y Mn 1-x-y ]O 2 are dependent on their chemical compositions in the temperature range. More specifically, the delivered capacity is higher for high Ni composition due to their high electric conductivity, whereas the operation voltage becomes lower at high rates. The AC impedance results indicate that the charge-transfer resistances are proportional to the amount of Ni in the compounds: namely, the high resistances cause a low operation voltage and these phenomena become predominant as the test temperatures lowered further. The chronoamperometric data demonstrate that the passive layer grows relatively thick for the high Ni electrodes, affecting increment of cell resistances at low temperatures.