A Direct Comparison of Pilot-Scale Li-Ion Cells in the Formats PHEV1, Pouch, and 21700

Abstract

Li-ion cells of the industrially-relevant formats PHEV1 (prismatic), multi-layer pouch, and 21700 (cylindrical) are directly compared by experiments for the first time. All three cell formats were reproducibly built on pilot-scale with the same anode (graphite), cathode (NMC622), separator, and electrolyte allowing a direct comparison. The main differences between these formats are their capacities (24.6 Ah, 2.2 Ah, 2.3 Ah), volume/surface ratios, as well as tab and the jellyroll/stack configurations (flat-wound, stacked, wound). The comparison involves voltage curves during formation (0.1 C), discharge rate capability (0.5 C−3 C), heating behaviour, cell impedances, geometrical properties such as electrode curvatures and tab configurations, as well as comparison with coin half cells with anode and cathode vs Li counter electrode. The data are put into context with commercial and pilot-line built cells from other studies.

Increase of Cycling Stability in Pilot-Scale 21700 Format Li-Ion Cells by Foil Tab Design

“…In the formation (left hand side of Figure 3b), both tab designs show similar areal discharge capacities (except for one outlier). For higher C-rates differences become visible (compare Figure 3a), which is consistent with our previous direct comparisons with the same electrodes, electrolytes, and separators of pilot-line built 18,650 and 21,700 cells [5] as well as PHEV1, pouch, and 21,700 cells [14].…”

“…Different patents described cylindrical cell designs with continuous tabs made from the current collecting foils ("tabless design") in cylindrical cells [11][12][13]. Additionally, flat wound jellyrolls in PHEV1 cells utilize also the uncoated border of electrodes for electronic connection to the terminals [14]. However, the effect of tabs made from foils in comparison with the conventionally welded tabs is to the best of our knowledge not described in the literature, although it could potentially lead to improved cycle life due to increased homogeneity of the jellyroll.…”

Effects of Tab Design in 21700 Li‐Ion Cells: Improvements of Cell Impedance, Rate Capability, and Cycling Aging

“…It is known that the cell impedance additionally depends on the coated cathode area. [5,27] The cell impedance decreases inversely with the cathode area, similarly to resistors connected in parallel. [5] For example, small lab cells show higher impedances than cylindrical cells (18650, 20700, and 21700), and the lowest impedances are observed for large cells (large pouch, PHEV1).…”

Reliable and flexible supercapacitors toward wide-temperature operation based on self-supporting SiC/CNT composite films

“…The reduced internal resistance and interfacial resistance are mainly related to the fact that the area of the sopackaged SC electrodes is larger than that of the hard-shell cell counterparts. 44 Accordingly, a specic capacitance of 9.09 F g À1 for a single electrode was achieved at the xed current density of 0.02 A g À1 (Fig. 4f).…”