Theoretical gravimetric capacity

The theoretical gravimetric capacity is the ratio of the amoimt of electricity which can theoretically be released by using all of the active material of an electrode or a secondary battery, to the mass of that active material. This value has to be calculated. For this reason, we sometimes find extremely high values, having nothing whatsoever to do with the reality of the situation, as is sometimes the case with lithium-air secondary batteries (see Chapter 10). 

The gravimetric capacity is expressed in Ah/kg. Calculations for determining theoretical gravimetric capacities are to be found in the chapters corresponding to the different technologies examined (sections 5.8, 6.3, 9.4 and 10.7). 

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In this section we will focus on four alanates with high practical potential such as NaAlH, LiAlH and Mg(AlH )2/Ca(AlH )2. Alanates with theoretical gravimetric capacities lower than that of NaAlH, being impractical for mobile applications, will not be discussed. 

The theoretical gravimetric capacity of this system is thus 11.5 wt% for 4 moles of H atoms to 1 mole of starting Li3N. In practice, the amount of stored hydrogen from nitride through to amide was found to be somewhat less, with uptake of 9.3 wt% and c. 10 wt% from gravimetric and volumetric measurements respectively. Taking the standard enthalpies of formation [41], the overall heat of the reaction in Eq. (16.5) was calculated to be... 

Materials Theoretical gravimetric capacity (mAh/g) Theoretical gravimetric capacity (mAh/g) with account taken of the degree of insertion Average practical gravimetric capacity (mAh/g) Cost... 

Exercise 6.1.- Calculate the theoretical gravimetric capacity and the gravimetric energy density of a C-LiCo02 element. 

We know (from section 5.3.1) that for this type of electrode, we must not exceed x = 0.5 for fear of disintegration of the structure. The theoretical gravimetric capacity is therefore ... 

The first materials to be studied were alloys based on aluminum (Al), tin (Sn) or silica (Si) i because of their very high theoretical gravimetric capacities. 

Considering the case of the Na-NiCl2 battery (equation [12.7]), the molar mass of active materials is, for 1 mole of NiCl2 and 2 moles of Na 58.7 + 2 X 35.5 + 2 X 23 = 175.7 g. With two moles of electrons exchanged, Faraday s law gives us the theoretical gravimetric capacity ... 

The nominal voltage per cell is, in this case, 2.35 V, the theoretical gravimetric capacity is 310 mAh/g and the theoretical gravimetric energy... 

With two moles of electrons exchanged, Faraday s law (see section 2.3.2.2) gives us the theoretical gravimetric capacity ... 

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