Novel A7B23-type La-Mg-Ni-Co compound for application on Ni-MH battery

The present work reports a new A(7)B(23) type layered structure in a La2Mg(Ni-0.8,Co-0.2)(9) alloy which has been prepared by casting and annealing. Based on the self-consistent identifications of X-ray diffraction, energy dispersive spectrometer and transmission electron microscope characterization, crystal structure of the new structure is confirmed to be trigonal crystal system (with the space group of P3 and cell parameters of a = 0.504 nm and c = 4.049 nm). The novel structure can be treated as composed of 10 [AB(5)] and [A(2)B(4)] unit block-layers stacking by [AB(5)]-[A(2)B(4)]-2[AB(5)]-[A(2)B(4)]-[AB(5)]-[A(2)B(4)]-2[AB(5)]-[A(2)B(4)] along the c-axis. The A7B23 type phase presents excellent discharge capacity and electrochemical cycling stability. Furthermore, the new structure possesses outstanding structural stability against hydrogen induced amorphization during gas-solid cyclings. Findings in the present work demonstrate the possibility of constructing the new RE-Mg-NI layered compounds by chemical elements substitution and also provides a possible prospect for development of the negative electrode alloys for Ni-MH battery.