Rapid Solidification Of Stoichiometric Cobalt Hydrogen Storage Alloy Phase Structure And Electrochemical Performance

In this paper, the La (NiMnM) x (x=5. 6~6. 0, M=Cu Al Fe, Sn) Co-free nonstoichiometric rare earth hydrogen storage alloys were studied. By means of DTA, XRD analysis, SEM/EDS investigation and electrochemical measurements, the effects of chemical composition, the composition and the preparation process such as annealing and rapidly quenching on the phase structures and electrochemical properties were studied systemically.La(NiMnM)6.0(M=Cu,Cr,Sn, Co) melt-spun alloys (>30m/s) and annealed alloys at lower temperature (<500C) consist of single LaNi5 phase with CaCu6 type crystal structure. Annealed at higher temperature, it changed to two phases. The electrochemical performance measurement shows that the melt-spun alloys have the more activation number (usually 7to 10 times), and lower discharge capacity, higher cycle stability. After annealing, the activation property is largely improved, and higher discharge capacity, lower cycle stability. After Ni replaced different elements by annealed high temperature , the alloy of CuO. 2 have hige discharge capacity (299mAh/g) and low cycle stability(Sioo= 86%) ;But the alloy of Sn have lower discharge capacity(2116mAh/g) and higher cycle stability(S100= 97%).La (NiMnM) 5.6 (M=Cu, Al, Fe, Sn) melt-spun alloys (>30m/s) and annealed alloys at lower temperature (400*C X lh) consist of single LaNi5 phase with CaCu5 type crystal structure. Melt-spun alloys remain fine and homogenous cellular and strip structure. After annealed at low temperature, crystal grains grow up, stucture pattern changed. The electrochemical performance measurement shows the discharge capacity of LaNi4.68Mn0.93 is higher than AB6.0, and lower cycle stability. After replaced Sn Cu Al Fe,melt-spun alloys of Al, Fe increase discharge capacity and cycle stability, Cu> Sn reduce discharge capacity and increase cycle stability. After annealing, improveing activation property, increasing discharge capacity and reducing cycle stability.Among all the melt-spun and melt-spun+annealed.alloy samples prepared, the one with LaNi4.48Mn0.93Al0.2, and annealed at 400C for lh has the best general performance: its activation number 4 times, the maximum discharge capacity Cmax=311mAh/g, high-rate discharge ability HRD600=79.25%, and capacity retention S100=89% after 100 cycles.It is seen therefore that nonstochiometric hydrogen storage alloys after melt-spun and low temperature annealing will have an improved electrochemical properties with decreased usage of cobalt metal.