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27.–28. April 2023
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Cost and performance analysis as a valuable tool for battery research: the case of the optimization of the low cut-off voltage of sodium-ion battery cells

Poster

  • P1-049

Author:

  • Simon Beringer

Other authors:

  • Alessandro Innocenti, Stefano Passerini

Institution/company:

  • Karlsruhe Institute for Technology
The widespread use of lithium-ion batteries for renewable energy storage and electromobility is enabling our society to shift from a carbon-based economy to a more sustainable one. However, issues in the supply of the critical materials required for their production could harm the deployment of the necessary battery capacity. An alternative with a high technological readiness level is the use of sodium-ion batteries. Although having usually a lower energy density than their lithium counterpart, they stand out thanks to their cheaper active materials, whose precursors are available in large quantities over the whole globe. To understand whether this new class of batteries can be competitive with the state-of-the-art, the cost and performance analysis is a fundamental tool that can support and rationalize the research of innovative anode and cathode materials.
An example is here given regarding the optimization of the lower cut-off voltage of sodium-ion batteries. In literature, some sodium-ion cathode materials are cycled in a very large voltage window, down to potentials below 2 V, to obtain a high specific capacity. Combined with the sloping potential of hard carbon anodes, the cell voltage can easily drop below 1 V while discharging. In battery packs, the nominal voltage is commonly indicated by the open circuit voltage at 50% state of charge. Nevertheless, to guarantee a constant power supply even at the end of the discharge, the battery must be oversized to satisfy the energy and power requirements, i.e., to provide higher current at low state of charge. The low voltage at the end of the discharge has then a negative effect on the cost per kWh and energy density. Hence, adjusting the voltage at which the discharge is ended, i.e., the lower cut-off voltage, can avoid a detrimental oversizing of the battery pack.
The effect of the lower cut-off voltage is simulated by using a modified version of the software BatPaC 5.0, which let us optimize the sodium-ion battery packs in terms of energy density and of cost per unit energy, to find the best compromise between a higher average voltage and a decreased available capacity of the battery. Several sodium-ion cathodes with different chemistries were included in the analysis, coupling them with a commercial hard carbon anode.&nbsp“;“
From the figures it can be seen how the two parameters have an exponential relationship with the initial cut-off voltage of the materials before the optimization. These results show how the capacity of sodium-ion cathodes can be fully and effectively exploited only if it lies above a certain voltage threshold, indicatively, 1.5 V after subtracting the hard carbon potential.
The described approach can be extended to innovative battery chemistries exploiting rather large operative voltage ranges such us those employing polyvalent cations.