Structure and electrochemical properties of LaCo 11− x− yNi xM y (M = Fe, Mn and Al) compounds

Abstract

In this work, the crystal structure and electrochemical charge–discharge properties of LaCo 13− x− y Ni x M y (M = Fe, Mn and Al) were studied. It was found that, in Co-rich region, except for the LaCo 11.4Ni 0.8Mn 0.8 sample, all the samples are composed mainly of the LaCo 13-type compounds. However, the 1:13 structure is difficult to obtain in Ni-rich samples. For the 1:13-type structure compounds. The lattice parameter and cell volume of compounds decrease with the substitution of Ni for Co and increase with the substitution of Al, Mn, Fe for Co. The electrochemical capacities of LaCo 12.2− y Ni 0.8M y (M = Fe, Mn, Al and y = 0.4 or 0.8) and LaCo 11− y Ni 2Al y ( y = 0, 0.5, 1.0) increase with increasing temperature. Compared with LaCo 13− x Ni x ( x = 0.8 and 2) compounds, the substitution of Mn or Al for Co results in decreasing of electrochemical capacity in the temperature range of 25–80 °C. The lowest electrochemical capacity was obtained from LaCo 11.8Ni 0.8Mn 0.4 compound. For the LaCo 13− x Ni x compounds, the electrochemical capacity increases in the temperature range 25–70 °C and decreases in the temperature range 70–80 °C with increasing Ni content x from 0.8 to 2. The best electrochemical properties of all the compounds studied here were obtained from LaCo 11.4Ni 0.8Fe 0.8 compound. The electrochemical stability increases and active property decreases markedly when Co is substituted by Al.