Pack Level Chemistry Comparison

In this pack level chemistry comparison we have taken some generic chemistry values for NMC, LFP. LTO and NaB. Thus allowing us to do a very high comparison. The tool for this comparison is available in the Battery Calculations Workbook.

chemistry comparison in the high level battery calculations workbook
Left: Cell values, Right: Pack Values

Cell Data

For the cells we have Open Circuit Voltage (OCV) values as an average of the charge and discharge OCV values.

open circuit voltage versus SoC for different chemistry

The lowest value is LTO where the OCV at 50% SoC is 2.23V

The other interesting curve is that of Sodium Ion (NaB) as it has a significant range.

For the internal resistance it uses a DCIR Ohm-Ah value for each chemistry so that the value can be scaled against the Ah cell that you select. This then has a typical DCIR versus SoC curve for that chemistry. The peak discharge uses 10s pulse DCIR values and the continuous discharge uses 30s DCIR values.

The voltage limits have been set for each chemistry as generic:

LFPLTONaBNMC
Min Voltage [V]2.001.502.002.50
Max Voltage [V]3.652.704.004.20

This post has been built based on the support and sponsorship from: MAHLE Powertrain LtdThermo Fisher ScientificEatron TechnologiesAbout:Energy and Quarto Technical Services.

Pack Data

For the battery pack you need to set the number of cells in series and parallel. Essentially with these you are setting the operating voltage range and the pack capacity. Although, the step size for the voltage is determined by the chemistry and for the capacity this is determined by the cell capacity [Ah] and the number in parallel.

For the following calculations we have used these values, the aim being to create a battery pack that could deliver 200kW continuous and 500kW peak.

LFPLTONaBNMC
Series10816011496
Parallel642446
Cell nominal Voltage [v]3.272.233.093.67
Cell nominal Capacity [Ah]5020105
Cell DCIR 10s 50% SoC [mΩ]1.40.51020

The Lithium Titanate (LTO) chemistry shows perhaps the flatest power delivery and this pack has a total energy of just 28.5kWh compared to the NMC pack of 81kWh.

pack power versus state of charge for different chemistries

The cell mass for the LTO pack would be 770kg, for the NMC cells the mass would be around 300kg.

This calculation doesn’t take everything into account, but is designed to be a starting estimate from where you can then make detailed calculations and with data that has more fidelity.

pack level chemistry comparisons

The calculation is all open in the spreadsheet and hence totally up to you how you modify and play with the data.

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