Microstructures and electrochemical hydrogen storage performances of La_(0.75)Ce_(0.25)Ni_(3.80)Mn_(0.90)Cu_(0.30)(V_(0.81)Fe_(0.19))_x (x = 0 0.20) alloys

摘要

Electrochemical hydrogen storage performances of a La_(0.75)Ce_(0.25)Ni_(3.80)Mn_(0.90)Cu_(0.30) alloy are improved by adding V_(0.81)Fe_(0.19) combined with hyper-stoichiometry, and microstructures and electrochemical characteristics of La_(0.75)Ce_(0.25)Ni_(3.80)Mn_(0.90)Cu_(0.30)(V_(0.81)Fe_(0.19))x (x = 0-0.20) hydrogen storage alloys are investigated. X-ray diffraction and backscattered electron results indicate that all alloys are a LaNi_5 phase with a hexagonal CaCu_5-type structure and the lattice parameters a, c and cell volume V of the LaNi_5 phase decrease with increasing x value. The alloy electrodes keep excellent activation performance with increasing V_(0.81)Fe_(0.19) content. Maximum discharge capacity of alloy electrodes first increases from 330.2 (x = 0) to 335.4 (x = 0.10) mAh/g, and then decreases to 328.8 mAh/g (x = 0.20) with further increasing x value. The high rate dischargeability at the discharge current density of 1200 mA/g first increases from 67.2% (x = 0) to 76.7% (x = 0.10), and then decreases to 65.3% (x = 0.20). The cycling capacity retention rate at the 100th cycle increases from 52.3% (x = 0) to 77.9% (x = 0.20), which is mainly ascribed to the improvement of anti pulverization.