Sodium-ion batteries (SIBs) are gaining momentum, driven by highly fluctuating material costs, rising supply chain and ecological risks in the lithium-ion battery (LIB) industry. Postulated advantages of SIBs include a wide resource availability, lower cost and higher sustainability. However, sodium’s lower reduction potential, along with its larger and heavier ions, lead to decreased energy densities compared to LIBs
In order to quantify the differences in performance and sustainability, in our recent work we conducted comprehensive energy density calculations as well as a life cycle assessment for state-of-the-art SIB cells in comparison with LiFePO4//Graphite cells. The origin for the material selection are the materials commercially pursued and developed by SIB cell manufactures, distinguishing between layered oxide, polyanionic and prussian blue analogue (PBA) based cells. Next to the material demand and the calculated energy densities, the life cycle assessment also incorporates the energy and material consumption of cell production by adapting the mass-scale production model of Degen et al. 2023.
The energy density calculations reveal that gravimetrically all SIBs can reach similar energy densities to LFP/graphite cells, while only layered oxides reach comparable volumetric energy densities. Especially cells based on PBAs show significantly lower volumetric energy densities, due to their intrinsically lower crystallographic density. Moreover, the optimization of the hard carbon anode is crucial to reach competitive energy densities.
As a result of the cradle-to-gate life cycle assessment, the global warming potential (GWP) in kg CO2 eq. kWh-1 is determined for different cell chemistries and scenarios, among others contemplating varying electrode thicknesses and different hard carbon precursors. Moreover, the ability of the model to differentiate between the contributions of individual materials and battery components, as well as the single production steps to the total GWP, allows to determine the key contributors. On the poster the GWP for selected SIB cells, modelling a hard carbon anode vs. different cathode chemistries is illustrated. While the nickel based O3-NaNi0.45Zn0.05Mn0.4Ti0.1O2 (O3-ZNMT) layered oxide cell even slighlty undercuts the GWP of LFP/graphite cells, the remaining SIB cells show increased GWPs, mainly due to higher impact of the cathode active material and lower energy densities. It can be concluded that further increases in energy density and/or reduced impacts of the cathode active material will be necessary to reach or even undercut the GWP of LFP in all SIB material groups. However, despite their lower technological maturity SIBs already show the potential to compete with LFP cells in terms of energy density and GWP.