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

Abstract

Li-ion cells of the industrially relevant 21700 format are investigated experimentally by systematic variation of their tab design. To observe the effects of the tab design only, the cells are built on pilot scale using the same electrodes, electrolyte, and separator. Tabs are varied regarding 1) conventionally welded tabs and 2) tabs made from the electrodes’ foils (“foil tabs”), as well as the tab number. Conclusions are drawn on cell impedances, rate capability (0.5C–3C), heating behavior, and cycling aging. Cells with a multitab design show a reduced impedance (1 kHz) by 62%, an improved charging rate capability by ≈17% for 3C, an improved cycle stability by 26.5%, and charge throughput by 22.8%. For the check-ups at C/10, improvements in cycle life and charge throughput of 51.1% and 42.4% are observed, respectively. The improved cycle life is due to the reduction of inhomogeneities in the jellyrolls as observed by X-ray computed tomography. The data are put into context with cells from other studies to conclude the order of magnitude of the effects of tab design variation. Based on experimental findings, estimations are made for 46800 format cells regarding energy content and impedance.