Sodium-ion batteries (SIBs) are gaining attention in research and industry as a sustainable alternative to lithium-ion batteries (LIBs). However, the advantages of sodium over lithium in terms of accessibility, price, and environmental impact are currently not fully exploited because of inexperience in production, leading to inhomogeneities in their behavior. Using electrical (e.g., open-circuit voltage curve (OCV), electrochemical impedance spectroscopy) and non-electrical measurement methods (e.g., laser scanning microscopy, computed tomography), three widely used LIB technologies and one SIB technology, all with the same rated capacity (1500 mAh) and format (18650), are compared in this article. The study reveals significant differences, such as a 12% lower cell weight at the same rated capacity of the SIB using less windings in the jelly roll, as well as a high energy density cell configuration and a much more severe dependency of the discharge capacity on temperature, exceeding the LIBs by at least a factor of 5. Additionally, the impedance of the SIB differs due to slower ion kinetics on the electrodes, showing relevant differences in both the frequency behavior and the pulse relaxation to the LIBs. An OCV reconstruction indicates the sparsity in the available literature data and the necessity to further investigate the characteristics of the SIB to validate it as a drop-in technology on the market.

This study investigates the design and geometric properties of high-power and low-temperature 18650 and 26650 lithium iron phosphate (LFP) cells. The analysis focuses on the geometry and components’ thicknesses and deriving CAD models for both cell formats. Design variations were observed, even within cells from the same manufacturer. For instance, one manufacturer’s 26650 cell was not a scaled-up version of their 18650 cell, and no equivalence was found between the designs of high-power and low-temperature cells from the same manufacturer. Thus, modifications are not purely chemistry based. The results also reveal deviations from the literature values for jelly roll component thicknesses, with anode current collectors averaging 61 µm and cathode current collectors averaging 60 µm. Coating thicknesses varied, with anode coatings averaging 32 µm and cathode coatings averaging 52 µm. These variations in current collector and coating thicknesses suggest that both high-power and low-temperature LFP cell designs differ from the typical literature values. Furthermore, a trade-off was observed between low-temperature operation with two-tab designs and high pulse capability with limited minimum operating temperatures. Additionally, smaller particle sizes in anode coatings were associated with lower impedance.

As Lithium-ion batteries need to be operated within a narrow temperature window to avoid power loss or safety issues, precise knowledge of the battery cell’s behaviour is crucial. Regularly, the surface temperature is used to estimate a battery cell’s temperature, leading to deviations due to thermal hot spots within the cell or pack. Here, real-time temperature changes can be tracked by utilising temperature-dependent electrochemical impedance during current-pulse relaxation, with the impedance directly transformed using a look-up table. The impedance-based measurement is therefore performed using different cylindrical cells (18650 and 21700) with embedded sensors, thereby avoiding prolonged thermal gradients. The proposed method shows average RMSEs of 0.4876K (18650) and 0.4573K (21700) at an ambient temperature of 20°C, using a dynamic load profile as a benchmark. The results are further compared with model-based approaches, revealing accuracy similar to that of a lumped thermal model, without the need for temperature measurements on the cell surface.

This study investigates the temperature-dependence performance of high-power lithium iron phosphate (LFP) cells for automotive starter batteries. Temperature effects on high-power LFP cells are contextualised based on pertinent literature in order to compare the typical capacity behaviour of lead–acid batteries with LFP. Experiments were conducted on five cylindrical LFP cell types in a thermal chamber across ambient temperatures from +45 °C to −30 °C using a 9 C discharge regime aligned with automotive standards. Electrical and thermal behaviours were analysed, including energy yield, power output, and surface temperature monitored by sensors and thermal imaging for room temperature. Energy output decreased exponentially with temperature but remained above 70% for most LFP cells at −18 °C, while only one cell type was functional at −30 °C. Thermal analysis at ambient temperature confirmed homogeneous temperature distribution without hotspots and low overall heating (from 2 °C to 14 °C), indicating no need for additional cooling for starter battery applications. A conservative power analysis indicated that 4 kW at −30 °C would require a 28P4S 26650 configuration, representing a lower-bound estimate. We argue that even this conservative figure suggests a potential for weight reduction compared with lead–acid systems. Energy-based Pb-equivalence factors of approximately 1.2 at −18 °C and 3 at −30 °C were derived. A preliminary guideline for cell dimensioning based on measurements at 25 °C is proposed to address discrepancies between data sheet specifications and actual performance for pack configuration based on required power.