Ca3(PO4)2 coating of spherical Ni(OH)2 cathode materials for Ni–MH batteries at elevated temperature

Calcium phosphate was used for surface modification of spherical nickel hydroxide to improve its high temperature performance at the first time due to its low cost. The Ca3(PO4)2 and Co(OH)2 coated nickel hydroxides were prepared by precipitation of Ca3(PO4)2 on the surface of spherical nickel hydroxide, followed by precipitation of Co(OH)2 on its surface. The optimum coating content of calcium was around 2% (atomic concentration) to obtain high discharge capacity both at 25 and 60 °C. It was shown that the discharge capacity of nickel hydroxide at higher temperatures was improved by coating of Ca3(PO4)2 and cobalt hydroxide. The high temperature performances of the sealed AA-sized nickel–metal hydride (Ni–MH) batteries using Ca/Co coated nickel hydroxide as positive electrodes were carried out, showing much better than those using uncoated or only Co(OH)2 coated nickel hydroxide electrodes. The charge acceptance of the battery using 2% Ca and 2% Co coated nickel hydroxide reached 81% at 60 °C, where the charge acceptances for uncoated and only Co(OH)2 coated nickel hydroxide were only 42 and 48%, respectively. It has shown that the Ca/Co coating is an effective way to improve the high temperature performance of nickel hydroxide for nickel–metal hydride batteries. It is a promising cathode material of Ni–MH batteries for EV applications due to the cost.