Effect of small amounts of Li on microstructures and electrochemical properties of non-stoichiometric low-Co AB_5-type alloys

摘要

The structure and electrochemical properties of low cobalt AB_5-type hydrogen storage electrode alloys with a small amount of Li in the A site have been investigated. With the increase of Li contents, the discharge capacity increases firstly from 240 mAh/g (x = 0) to 328 mAh/g (x = 0.1) and then decreases to 320 mAh/g (x = 0.2). The cycle stability is improved slightly and the electrochemical capacity can remain 71.4% (x = 0.2) after 230 charge/discharge cycles. The alloy (x ≤ 0.1) showed the best rate discharge ability under the discharge current density of 1200 mA/g. It is found that as-prepared alloys are basically composed of LaNi_5 as the matrix phase and LaNi_3 as the second phase (x ≤ 0.1). But the abundance of LaNi_3 phase dramatically decreases with increasing x. When x = 0.2, a new phase having a chemical composition of Al(NiCo)_3 was observed.