| Work Detail |
German researchers have compared the electrical behaviour of sodium-ion batteries with that of lithium-iron-phosphate batteries at different temperatures and charge states. Their work shows how the charge state during cycles significantly affects the efficiency of sodium-ion devices. Researchers from the Technical University of Munich (TUM) and RWTH Aachen University (Germany) have compared the electrical performance of high-energy sodium-ion batteries (SIBs) with that of a state-of-the-art high-energy lithium-ion battery (LIB) with lithium iron phosphate (LFP) cathode and found that state of charge and temperature have a greater influence on the impulse resistance and impedance of SIBs than of LIBs. “SIBs are often considered as a drop-in replacement for LIBs,” the scientists say. “However, differences in the electrochemical behaviour of sodium and lithium require adaptations at both the anode and cathode. While graphite is commonly used as the anode material for LIBs, hard carbon is currently considered the most promising material for SIBs.” They also explained that their work aimed to fill a gap in research, as there is still a lack of knowledge about the electrical behavior of SIBs in terms of varying temperatures and states of charge (SOCs). The research team carried out, in particular, electrical performance measurements at temperatures between 10°C and 45°C and open circuit voltage measurements of the entire cell at different temperatures, as well as half-cell measurements of the corresponding cells at 25°C. “In addition, we investigated the influence of temperature and SOC on both DC resistance (R DC) and galvanostatic electrochemical impedance spectroscopy (GEIS),” he specified. “To examine usable capacity, usable energy, and power efficiency under dynamic conditions, we performed rate capacity tests by applying different charging rates at different temperatures.” Measurements were performed on a LIB, a SIB based on a nickel-manganese-iron cathode and a LIB with a LFP cathode, and all devices were found to exhibit hysteresis in the open circuit voltage between charging and discharging. “Interestingly, in the case of SIBs, hysteresis occurs mostly at low SOCs, which, according to half-cell measurements, is probably due to the hard carbon anode,” the academics emphasize. “The R DC and impedance of the LIB show very little dependence on the SOC. In contrast, in the case of SIBs, R DC and impedance increase significantly at SOCs below 30%, while higher SOCs have the opposite effect and lead to lower R DC and impedance values.” Furthermore, they found that the temperature dependence of R DC and impedance is larger for SIBs than for LIBs. “LIB tests show no significant influence of SOC on round-trip efficiency. Instead, cycling SIBs from 50% to 100% SOC can reduce efficiency losses by more than half compared to cycling from 0% to 50%,” they further explained, noting that SIB efficiency grows dramatically when cycling cells in a higher SOC range compared to a lower SOC range. Their findings are published in the study “ Comparing the electrical performance of commercial sodium-ion and lithium-iron-phosphate batteries,” published in the Journal of Power Sources . “Our results indicate that the state of charge during cycling significantly affects the efficiency of sodium-ion batteries and should therefore be taken into account,” they conclude. |
