Effect of AlPO4-coating on cathodic behaviour of Li(Ni0.8Co0.2)O2

• Published in: Journal of power sources Vol. 141; no. 1; pp. 129 - 142
• Main Authors: TAN, K. S, REDDY, M. V, SUBBA RAO, G. V, CHOWDARI, B. V. R
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier Sequoia 16.02.2005
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Oxygen; Oxide layer; Cathode; Thermal behavior; Li(Ni0.8Co0.2)O2; Lattice parameters; Phase transitions; Li-ion batteries; Discharge charge cycle; Thermal stability; Cyclic voltammetry; AlPO4-coating; Nickel; X ray diffractometry; Protective coatings; Lithium ion
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2004.08.044

The cathodic behaviour and thermal stability in the charged state of bare and 1-8wt.% AlPO4-coated layered oxide Li(Ni0.8Co0.2)O2 are investigated. The synthesized compounds are characterized by a wide variety of techniques. X-ray diffraction analysis (XRD) shows that the hexagonal a and c lattice parameters of Li(Ni0.8Co0.2)O2 are not affected by the AlPO4-coating, but there are indications of an increasing number of Ni-ions occupying the Li-sites in the Li-layer with increasing amounts of the coated AlPO4. The O 1s X-ray photoelectron spectra clearly indicate two different oxygens that correspond to the coated-AlPO4 and the bare compounds. Cyclic voltammetry (2.5-4.3V) shows that the characteristic structural phase transitions exhibited by the bare compound are suppressed by > =5wt.% AlPO4-coating. Galvanostatic charge-discharge cycling has been carried out at a current density of 30mAg-1 in the range of 2.5-4.3V up to 70 cycles and 2.5-4.5V up to 40 cycles. Capacity-fading of the 3 and 5wt.% AlPO4-coated Li(Ni0.8Co0.2)O2 is much less than that shown by the bare compound, which is 21% between 10 and 70 cycles with a 4.3V cut-off and 48% between 10 and 40 cycles with a 4.5V cut-off. The coulombic efficiency is > 98% in all cases after a few initial cycles. Impedance spectra of cells with 1 and 5wt.% AlPO4-coated compounds and ex situ XRD of the 3 and 5wt.% AlPO4-coated charged cathodes are examined and the results interpreted. Differential scanning calorimetry curves of the charged cathodes (4.3V) reveals that the decomposition temperature of 220 deg C for the bare compound is increased by 10 deg C after 3 and 5wt.% AlPO4-coating, and more significantly the heat evolution decreases by a factor of 5, which indicates better thermal stability. Nevertheless, this benefit comes at the expense of reversible capacities, which decrease from 202mAhg-1 (fifth cycle, 4.3V) for the bare compound, to 156 and 100mAhg-1 for the 3 and 5wt.% AlPO4-coated Li(Ni0.8Co0.2)O2, respectively.