Review: on rare-earth perovskite-type negative electrodes in nickel–hydride (Ni/H) secondary batteries

The development of renewable sources, in the electronic and automotive industry have led engineering to limit its impact on the environment and transform energy associated technologies into sustainable and environmentally friendly devices. In the fields of energy storage and conversion, rechargeable batteries have experienced constant advances in their architecture and materials to get a better performance with a lower environmental cost [ 1 – 3 ]. Among the various rechargeable battery technologies, nickel–metal hydride (Ni/MH) and lithium ion (Li-ion) batteries have experienced continuous development in the last decades. The Ni/MH battery has a relatively low nominal voltage value (1.2 V) with a voltage window ranging from 0.6 to 1.5 V when compared to the rival Li-ion battery (nominal voltage 3.6 V with a voltage window from 3.0 to 4.2 V). Having a lower voltage means that more Ni/MH cells connected in series in a battery pack are required to achieve a pre-determined pack voltage (for instance, three Ni/MH cells instead of one Li-ion cell for a pack voltage of 3.6 V). The Ni/MH battery also has a relatively high energy density (Wh L −1 ) but a rather low specific energy (Wh kg −1 ) when compared to the Li-ion battery as a result of the high density of its active materials in the anode (nickel-based alloys versus graphite) [ 4 ]. Thus, Ni/MH batteries are widely used in stationary applications, consumer electronics, power tools, hybrid and full electric road and rail vehicles because of its durability, abuse tolerance, compact size, and environmental friendliness [ 5 – 8 ]. On the other hand, Li-ion batteries are commonly used in applications where strict requirements in power and energy are needed, such as in electric vehicles and mobile phones [ 4 , 9 ].