The effect of cobalt on the electrochemical performances of Ni-Al layered double hydroxides used in Ni-M(H) battery

A series of cobalt-substituted Ni-Al layered double hydroxides (LDHs) with the molar ratio of Co and/or Ni to Al of 4 synthesized by the method of urea homogeneous coprecipitation have been investigated as the positive material for Ni-M(H) battery. With more Co2+ substitution for Ni2+, the crystal parameter of enlarges, as well as the crystal size calculated by the Scherer equation according to their XRD patterns. Electrochemical characterizations reveal that cobalt improves electrochemical performance at high current densities. For example, the maximum discharge capacity of Ni3.2Co0.8Al LDH and Ni3CoAl LDH under a current density of 800 mA g−1 are 205 mA h g−1 and 204 mA h g−1 respectively, while that of the as-prepared Ni4Al LDH by the same method is only 152 mA h g−1 under the same condition. Together with the investigations on the electrochemical behaviors of two mixed electrode materials, Ni4Al LDH surface coated by Co4Al LDH and that by simple mechanical mixing, it can be concluded that surface coating is the most effective way to obtain higher discharge capacity at higher current density.