Effects of F-treatment on degradation of Mg2Ni electrode fabricated by mechanical alloying

The effects of surface fluorination on the electrochemical charge–discharge properties of a Mg2Ni electrode, prepared by mechanical alloying in Ni-MH batteries are investigated. After 20 h milling, Mg and Ni powder form nanocrystalline Mg2Ni. The discharge capacity of this alloy increases greatly on the initial cycle but, due to the formation of a Mg(OH)2 passive layer, displays rapid degradation in alkaline solution within 10 cycles. In a 6 M KOH+x M KF electrolyte (x=0.5, 1, and 2), a continuous and stable fluorinated layer is formed and the durability of the Mg2Ni electrode increases marketly and a high rate discharge capability is obtained (90–100 mAh/g). Addition of 2 M KF leads to the highest durability of all the electrodes tested. The improvement is due to a thin MgF2—flourinated layer, which reduces the charge-transfer resistance and protects the Mg2Ni electrode from forming a Mg(OH)2 layer.