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

Abstract

Li-ion cells of the industrially-relevant 21700 format were built on pilot-scale with tabs made from (a) the electrodes’ current collecting foils (Al and Cu, “foil tabs”) in comparison with (b) conventional tabs (Al and Ni) welded to the electrodes’ current collecting foils (“welded tabs”). Both cell types use the same anode (graphite), cathode (NMC622), separator, electrolyte, as well as the same tab positions. This allows a direct comparison of welded tabs and foil tabs regarding formation, C-rate capability, cell electrical resistance, and long-term cycling stability tests. Our data reproducibly shows 14.4% longer cycling stability and 11.2% increased total charge throughput in the case of the cells with foil tabs until 80% SOH, which is likely due to less inhomogeneities in the case of the foil tab design.

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

“…The reason is the lower cross section of the foil tabs. [ 19 ] This difference between foil and welded tabs is the strongest for the 1 × 1 configuration, corresponding to a decrease of 44% (foil tabs) and 46% (welded tabs) in the 1 × 2 configuration.…”

“…The reason is most likely the lower cross‐sectional area of the foil tabs and therefore their higher impedance. [ 19 ]…”

“…[19] The cells with foil tabs were able to show 14.4% more cycles and showed 11.2% more total charge throughput until 80% state-of-health (SOH). [19] We speculated that the absence of inhomogeneities with foil tabs leads to the improved cycling stability. [19] Although there are many simulations on the influence of the tab design in pouch cells, [20][21][22] experimental results on cylindrical cells are rather scarce.…”

“…[19] We speculated that the absence of inhomogeneities with foil tabs leads to the improved cycling stability. [19] Although there are many simulations on the influence of the tab design in pouch cells, [20][21][22] experimental results on cylindrical cells are rather scarce. Simulations on the influence of tab design on the performance 18650, 21700, and 26650 cells were recently presented by Sturm et al [23] The authors showed that the increase of the tab number has a strong influence on the fast-charging capability.…”

“…[1,5,19] Recently, we showed that cells with tabs made from the electrode's foils instead of welded tabs show an improved cycle life. [19] The cells with foil tabs were able to show 14.4% more cycles and showed 11.2% more total charge throughput until 80% state-of-health (SOH). [19] We speculated that the absence of inhomogeneities with foil tabs leads to the improved cycling stability.…”