Published online by Cambridge University Press: 10 February 2011
Two crucial characteristics are expected for batteries. One is large capacity (large energy density) and the other high power. In the last decade, the batteries with large capacity and energy density have been strongly required in the field of portable electronics and communication equipments and, hence, the new batteries such as Ni-MH and Li-ion ones have been developed and commercialized. At present, Ui-ion battery has the largest energy density of all the available batteries and its energy density has come up to 300WM/l, twice as large as that of Ni-Cd one. In general, electric power of batteries signifies the amount of energy put out at unit time. Thus the output power discharged from a battery, storing a certain amount of capacity, in Ihour is ten times as much as that discharged in 10 hours. It is indeed an excellent ability to go on walking all the way with a heavy knapsack on one's back but so is it to output a tremendous power at a moment just as in the weightlifting. It is well known that Ni-Cd battery can output the highest power of all the batteries. It can be discharged at about 10C, namely in about 6 minutes. Large energy density and high output power seem to be similar, but they are essentially different.