Practical gravimetric energy density

The gravimetric and volumetric energy densities will be very different depending on the nature of the electrodes. Also, we need to clearly distinguish between the gravimetric and volumetric energy densities of a cell 

State-of-charge estimation for lithium-ion batteries under various operating conditions using an equivalent circuit model . Computers and Chemical Engineering, 41, 1-9, 2012. 

Fleischer, D.U. Sauer, On-line estimation of hthium-ion battery impedance parameters using a novel varied-parameters approach , J. Power Sources, forthcoming. 

Battery packs, including the BMS, are usually assembled using cylindrical elements (in the area of portable computers, we speak of cells), labeled 18650 (because their dimensions are standardized 18 mm in diameter and 65 mm in length). We can now sometimes find so-called 26650 formats (26 mm in diameter and 65 mm in length) introduced by 

27 In order to valorize hthium-ion batteries in comparison to other less recent technologies, the gravimetric capacity of a cell is often quoted, rather than that of a pack. 

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On the scale of a cell, the practical gravimetric energy density ranges from 25 to 35 Wh/kg o considering only the liquid electrolytes. 

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. 

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