Batteries theoretical energy

The theoretical data [1] shows that Li and Ca possess very high energy density (13172 and 4560 Ah/kg respectively) but these metals are not suitable to be used as anodes because of their instability in aqueous electrolytes. The theoretical energy densities of Mg and A1 are also high (6846 Wh/kg and 8212 Wh/kg). It is shown that some alloys of Mg and A1 can be successfully used as anodes, especially in metal-air cells with neutral electrolytes. The theoretical energy density of Zn is much lower than that of Li and Ca, but the self-discharge of Zn can be effectively suppressed by the use of suitable inhibitors. That s why the zinc-air batteries with KOH electrolyte are the first metal-air system brought into service. 

More recently, solid state batteries with lithium conducting polymer electrolytes have been extensively studied. The development has focused on secondary batteries for an electric vehicle, because lithium polymer batteries have a theoretical energy density that approaches 800 W h kg ... 

The Other Five Candidates. All the molten salt SBs reviewed above have either a Li anode or a lithium alloy, one in which Li prevails quantitatively. As to the other 5 light metals they are seldom mentioned in the literature as candidates for anodes in these SBs, except Al. In (82) it is stated that molten salt batteries with Ca or Mg anodes yield only a small proportion of their theoretical energy because (a) Ca anodes react chemically with the electrolyte, and (b) both Ca and Mg anodes are passivated at high current drains, becoming coated with resistive films of solid salts. In a melt containing Li salts, Ca replaces Li ions by the displacement reaction Ca + 2LiCl = CaCl2 + 2Li. 

Terms. TED - theoretical energy density (free energy of reaction/sum of molar wts of reactants) ED practical or realized Wh/kg SB - secondary or storage battery (rechargeable) dod - depth of discharge (% recharge removed before recharge) ... 

Calculate the theoretical energy density of a lead-acid battery at 25 °C. Assume that 1 mol each of lead and lead dioxide is discharged from an initial H2S04 concentration to final acid concentration. The 54 A hr are produced at room temperature in this discharge at an average voltage of 2 V. Base your calculations only on moles of the three active materials, i.e., lead, lead dioxide, and sulfuric acid. (Bhardwaj)... 

The theoretical energy density of lead-acid batteries is only 171 W h/kg, as a result of the high atomic weight of lead. The practical energy density depends on the rate of discharge, as seen in Fig. IM, but even at low rates it does not exceed about 40 W h/kg. This... 

The largest asset of lead-acid batteries is their low price, compared to any other secondary battery currently available. The energy density is inherently low, but in its main application as a car battery this is tolerable. For application as the main power source of electric vehicles, an energy density of at least 100 W h/kg is necessary. This corresponds to 58% of the theoretical energy density - a very difficult goal. Power density is another limitation, particularly since increasing the power decreases the energy density substantially. 

Battery Theoretical OCV, V Actual OCV, V Theoretical specific energy, Wh/kg Actual specific energy, Wh/kg... 

The high ionization potential and the very low density of the metals are promising to make use of them in high-temperature batteries Electrochemical cells using lithium as anode, a solid ceramic electrolyte and lithium polysulphide as cathode may reach a theoretical energy density of 3000 Wh kg- . Problems are caused by the bad compatibility of lithium with ceramic materials. 

The theoretical energy density of a lithium-sulfur electrochemical system is 2500 Wh/kg or 2800 Wh/1, which makes it immensely attractive for the development of a chemical power source. This attractiveness is also enhanced by the ready availability and cheapness of sulfur and the absence of environmentally harmful components. And, indeed, attempts of developing a battery using this electrochemical system were made yet in the end of the 1960s of the previous century, at the rise of the studies of electrochemical lithium systems. It was suggested in the beginning to use the negative electrode made of metallic lithium and the positive one of elementary sulfur supported directly on the current collector. The characteristics of these first layouts were clearly unsatisfactory, partly, because sulfur is an insulator. Later, the positive electrode came to be made of a mixture of sulfur and a carbon material (carbon black). 

The long-term batteries are notable for a return to ambient-temperature, aqueous electrolyte cells. Particularly, the Al/air battery shows a huge theoretical energy density (10% of this value would be very acceptable ). The cells require fundamental advances in electrochemistry to be really successful (with the Al/air cell an improvement at both electrodes is necessary). Hence the trend is clear. A major problem is associated with power density and this highlights the need to improve electrode kinetics and the design of active materials to permit more rapid discharge. 

Figure 5.21 Theoretical energy density of a Li/conductive polymer battery. (Assumed cell voltage 3.0 V.)...

The lead-acid battery Pb/H2S04/Pb02 [1] provides a fast cell discharge at 2.0 V, it is relatively low-cost, and 98% of the batteries used in the USA are recycled. This battery has dominated the market for rechargeable batteries, but Pb is heavy and the practical energy density of the battery is only about 25% of its limited theoretical energy density (Wh/kg). Therefore, other secondary batteries are used for handheld devices and contend for the electric-vehicle market. 

This type of calculation can be useful as a means of comparing the theoretical specific energies of different batteries. Practical energy densities are design dependent and typically deliver no more than 20-40% of the theoretical specific energy. 

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