Phase Structure And Electrochemical Performance Study Of Rapid Quenching LaMgNi_3.6M_0.4（M=Ni, Co, Al） Alloy

The popularity of electric cars brings urgent demand for power batteries. With itslarge discharge current and high safety performance, Ni-MH battery has a broad space fordevelopment in the field of power battery. However, the actual discharge capacity of LaNi5Ni-MH battery applied in commerce, is already very close to its theoretical capacity348mAh·g-1. Therefore, it is the key to the development of Ni-MH battery to exploit newnegative electrode materials with high capacity for Ni-MH battery. Among negativeelectrode materials of Ni-MH batteries, the theoretical capacity of LaMgNi4alloy is up to470mAh g-1,which will be negative electrode materials of Ni-MH battery, possiblyreplacing commercial AB5hydrogen storage alloy in the near future.By replacing a small amount of Ni in LaMgNi4with Co, Al, Cu and Mn, it finds thatof LaMgNi3.6Co0.4and LaMgNi3.6Al0.4show better capacity. On the basis of previousresearches, thin sheet samples were obtained at a cooling speed of1,3,5and10m/s usingvacuum rapid quenching. Then XRD, SEM and EDS of the samples were analyzed.Results showed that multiphase structures were found in LaMgNi4, as well asLaMgNi3.6Co0.4and LaMgNi3.6Al0.4. Same phase compositions were discovered inLaMgNi3.6Co0.4and LaMgNi4, that is LaNi5and LaMgNi5. While, fewer amount of LaNi5were observed in LaMgNi3.6Co0.4, and the content of LaNi5phase was significantlyreduced with the increasing of cooling speed. LaMgNi4and LaAlNi4were the main phasecompositions of LaMgNi3.6Al0.4, without large changes with rotate speed increasing. SEMand EDS analysis indicated that lamellar structures were found in LaMgNi4andLaMgNi3.6Co0.4. What’s more, LaNi5was distributed in the center of crystalline grains,while LaMgNi4distributed on the edges. Though lamellar structures were found in SEMspectrum of LaMgNi3.6Al0.4, no obvious two phrase structure was presented at a coolingspeed of1m/s, while acicular crystal grains were found at a cooling speed of1m/s.Through EDS analysis for LaMgNi3.6Al0.4, acicular crystal grain in the alloy at3m/scooling speed was LaAlNi4, in the center of which was distributed LaMgNi4.The electrochemistry capacity analysis by LAND tester showed that the dischargecapacity of LaMgNi3.6Co0.4was obviously improved. The discharge capacity of LaMgNi4 reduced with cooling speed increasing, while that of LaMgNi3.6Co0.4increased, especiallyat10m/s, up to339.6mAh·g-1. The discharge capacity of LaMgNi3.6Al0.4significantlyreduced with a maximum only287mAh·g-1, which decreased largely with the increase ofrotate speed. The effect of element and rotate speed on the cycling stability of alloy showedthat no significant change was found on the stability of LaMgNi3.6Co0.4.While the cyclingstability of LaMgNi3.6Al0.4was obviously improved, and it was also significantly enhancedwith the increase of rotate speed.