Impact of Electrode and Cell Design on Fast Charging Capabilities of Cylindrical Lithium-Ion Batteries

Abstract

Cylindrical formats for high energy lithium-ion batteries shifted from 18650 to 21700 types offering higher volumetric energy density and lower manufacturing costs. Bigger formats such as 26650 may be of benefit as well, but longer electrodes and increased heat accumulation due to larger cell diameters are challenging for the batterys design and performance. An experimental review of state-of-the-art cylindrical lithium-ion batteries implies a delayed development of high energy 26650 cells. Optimized and prospective tab designs are discussed for high energy 18650, 21700 and 26650 formats using an experimentally-validated multi-dimensional multiphysics model of a silicon-graphite/nickel-rich lithium-ion battery. The model incorporates several 1D electrochemical models combined with a 2D electrical and a 3D thermal model. Novel in- and through-plane voltage-drop analysis reveals a dominant influence of the tab design on the cells total polarization, where a multi-tab instead of a single-tab design can improve the fast charging efficiency by up to +23% SoC. Fast charging profiles are adapted to tab design and cylindrical format, which prevent overheatings and the local onset of lithium plating across the active electrode area. Multi-tab design is recommended for high energy 26650 cells, but imbalances in SoC and temperature suggest alternative formats at slightly reduced cell diameters.