Whilst extensive research has been conducted on the effects of temperature in lithium-ion batteries, mechanical effects have not received as much attention despite their importance. In this work, the stress response in electrode particles is investigated through a pseudo-2D model with mechanically coupled diffusion physics. This model can predict the voltage, temperature and thickness change for a lithium cobalt oxide-graphite pouch cell agreeing well with experimental results. Simulations show that the stress level is overestimated by up to 50% using the standard pseudo-2D model (without stress enhanced diffusion), and stresses can accelerate the diffusion in solid phases and increase the discharge cell capacity by 5.4%. The evolution of stresses inside electrode particles and the stress inhomogeneity through the battery electrode have been illustrated. The stress level is determined by the gradients of lithium concentration, and large stresses are generated at the electrode-separator interface when high C-rates are applied, e.g. fast charging. The results can explain the experimental results of particle fragmentation close to the separator and provide novel insights to understand the local aging behaviors of battery cells and to inform improved battery control algorithms for longer lifetimes.

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.

The 18 650 and 21 700 cell format are state of the art for high-energy cylindrical lithium-ion batteries, while Tesla proposed the new 4680 format with a continuous ”tabless” design as the choice for electric vehicle applications. Using an experimentally validated multidimensional multiphysics model describing a high energy NMC811/Si-C cylindrical lithium-ion battery, the effects of tabless design and cooling topologies are evaluated for 18 650, 21 700, and 4680 cell formats under varying charging protocols. Mantle cooling is found to be the most efficient cooling topology for a segmented tab design, whereas tab cooling performs equally well for tabless cells and achieves better performance for the 4680 format. By massively reducing polarization drops (approx. 250 mV at 3C) and heat generation inside the current collectors (up to 99%), the tabless design increases cell homogeneity and enables format-independent scalability of fast-charging performance with a tab-cooling topology. In addition, the 0 to 0.8 SoC charge time can be reduced by 4 to 10 min compared to cells with a segmented tab design, resulting in 16.2 min for the 18 650 and 21 700, and 16.5 min for the larger 4680 cell format.