Comparing the electrical performance of commercial sodium-ion and lithium-iron-phosphate batteries

Commercial sodium-ion batteries with layered oxides as cathode material are available today. They can be produced with highly abundant raw materials and are considered environmentally friendly and cost-effective. Thus, sodium-ion batteries could replace lithium-ion batteries with lithium-iron-phosphate cathode on the market to some extent. However, a systematic evaluation of their electrical performance over different temperature ranges and a comparison to state-of-the-art lithium-ion batteries is still missing. In this study, we systematically compare the electrical performance of a high-energy and a high-power sodium-ion battery with a layered oxide cathode to a state-of-the-art high-energy lithium-ion battery with a lithium-iron-phosphate cathode for temperatures ranging from 10 °C to 45 °C. Both state-of-charge and temperature have a higher influence on the pulse resistance and the impedance of the sodium-ion batteries than the lithium-iron phosphate batteries. We show that in the low state-of-charge region, below 50 %, the energy efficiency losses of the sodium-ion batteries are approximately twice as high compared to cycling the cells above 50 % state-of-charge. This effect is even higher for the more application-oriented constant power instead of constant current measurements. Our findings indicate that the state-of-charge during cycling significantly affects the efficiency of sodium-ion batteries and should therefore be taken into account.