Batteries specific capacity

FIGURE 35.108 Rate capability of a SiTON/LiPON/LiCoOj battery. Specific capacity and volumetric edacity are based on the as-deposited mass and volume of SiTON. Courtesy of Oak Ridge National Laboratory. Reproduced from the Journal of Power Sources, Vol. 81, 1999, with permission from Elsevier Science.)... 

The supercapacitors described in the literature have an overall specific capacity of about 1 to 5 F/g (i.e., when allowing for the weight of the two electrodes, the leads, the electrolytes, and aU peripheral components). In them, electric energy can be accumulated with a density of 1 to 5 Wh/kg (which is one to two orders of mag-nimde less than in batteries). 

LiCo02, one of the most widely used cathode materials in lithium rechargeable batteries because of its high specific capacity, has been prepared in the form of... 

It can be seen that an energy of ca. 150 kJ/kg, comparable to that accumulated in Pb02-Pb or Ni-Cd batteries, can be obtained at voltages of 4V. Somewhat lower energy (100 kJ/kg) is accumulated at a voltage of 3V. Consequently, the searched system carbon/electrolyte should be characterised by (i) specific capacity. > 160 F per gram of activated carbon and (ii) electrochemical stability window at the level of ca. >3V. 

Table 2. Specific capacity, mAh/g, of LR2325 batteries based on various MnOz samples at different external loads (MnOz -Zn).

The iron-nickel oxide alkaline battery system has many features in common with the nickel-cadmium system discussed above. It was first developed by Edison in the USA at the turn of the century and was patented in the same year as Jungner s first nickel-cadmium US patent, 1901. Iron can be regarded as a favourable active battery material because of its low cost, high theoretical specific capacity (twice that of cadmium) and non-toxic, pollution-free characteristics. However, because its reduction potential is below that of hydrogen, and since hydrogen overvoltage is low on iron, charge retention is poor and efficiency is low. 

Li-silicon has a specific capacity greater than that of Li metal and a red-ox potential of <1V vs. Li/Li+. Extensive studies are carried out throughout the world in order to develop Si-C composites and intermetallic compounds containing silicon as novel anodes for high energy density, rechargeable lithium batteries. 

The high theoretical specific capacity (3862 Ah kg ) and capacity density (2047 Ah L" ) of the lithium-metal electrode, together with its promising redox potential, give the battery unique advantages in terms of specific energy and energy density. 

To avoid the problems associated with lithium metal, lithium insertion materials (e.g., graphitic carbons) are being investigated as negative electrodes. With respect to lithium metal, the use of negative insertion materials improves the cycle life and safety of the battery but lowers the cell voltage, the theoretical specific capacity, and the charge transfer rate [104]. 

---