Practical volumetric energy density

Exercise 6.5.-What are the volumetric energy densities of the cells and packs for portable computers discussed in exercises 6.2 to 6.4  

The solution to exercise 6.5 shows the substantial evolution of the volumetric energy density over those ten years for an 18650 cell, the value has increased from 400 to 600 Wh/L, which is a proportion of 150%. In the same vein, for an 11.1 V pack, it increases from 114 to 186Wh/kg. These values are higher than those quoted in Tables 6.11 and 6.12, because we have gone from dealing with a long-life industrial material to dealing with a material whose lifetime is much shorter (2-5 years). 

Plot of the gravimetric energy densities as a function of the volumetric energy densities 

We can consider that the electric vehicle (EV) application is on the boundary between a power-oriented and an energy-oriented application. Power is delivered in the form of peaks of current for a few seconds during the phases of acceleration or braking of the vehicle, but it is necessary to have sufficient energetic autonomy. For this type of application, the market is currently witnessing the apparition of elements with a prism format, which are easier to build into a pack and which have high capacities (e g. Kokam 3.7 V-100 Ah or 123Systems 3.3 V-100 Ah). 

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System Observed open circuit voltage (V) Practical volumetric energy density (Whcm-3)... 

The volume of the module is 300 L. This gives us a practical volumetric energy density of 100 Wh/L. 

The practical volumetric energy density is 36-171 Wh/dm as cells and 24-122Wh/dm as batteries. The batteries have a working voltage of 0.9-1.12 V/cell and require voltage regulation of 5% under fixed conditions. The operating temperature is... 

Commercial and non-commercial carbons were tested for their applicability as anode of lithium-ion battery. It was found that Superior Graphite Co s materials are characterized both by high reversible capacities and low irreversible capacities and thus can be regarded as good candidates for practical full cells. Cylindrical AA-size Li-ion cells manufactured using laboratory techniques on the basis of SL-20 anode had initial capacities over 500 mAh (volumetric energy density ca. 240 Wh/dm3). Boron-doped carbon... 

As the specific gravity was not disclosed, we assume a value of 2.0, which is rather large for an organic material. In this case, the volumetric energy density would be 1.2 Wh/cm, only about 45% compared to that of LCO whose energy density is 2.6 Wh/cm. Moreover, if the cutoff voltage is fixed to 3.0 V, the discharge capacity would be less than 50 mAh/g. So, this compound can hardly be considered practical and attractive as a cathode active material, even if it is free from rare metals. 

In the past, several reports for the practical-sized Li-S battery were found. For example, high energy cell over 300 Wh kg was manufactured by Sion Power, and it was proved not to reach the thermal runaway [20]. But at this stage, there has not been a commercially available Li-S cells. It still will need time to put this system into the market. One of the main drawbacks is the lower density of the material and electrolyte in addition to the problem already stated in this article. Volumetric energy density cannot be so advantageous as gravimetric energy density because of the lower density. 

The addition of seven equivalents of Li to AgV02 corresponds to a theoretical specific capacity of about 315 mAh, which results in a specific energy of 270 Wh/kg and a volumetric energy density ofWh/L for a practical Li-AgVOj cell. 

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