Effects of Non-Uniform Current Distribution on Energy Density of Li-Ion Cells

To quantify the impact of non-uniform current distribution in a large-format Li-ion cell on its overall energy density, five cell configurations with different positive tab numbers and locations were developed. This was enabled by a specially designed segmented cell with reconfigurable positive tabs on the outside. Current distribution and overall discharge performance were measured and correlated with each other for all five cell configurations. It is shown that tab number and location have significant effects on the performance and current distribution of a Li-ion battery cell. Fewer tabs typically cause lower performance but excessive tabs do not help. The 1-tab-co-located configuration causes both very non-uniform current distribution and very low overall discharge performance, and should be avoided in tab design for cells bigger than similar to 2.4Ah. The effects of tab configuration on overall performance can be attributed to and explained by current distribution. Discharge energy of the experimental cell decreases almost linearly with a current density non-uniformity factor. Non-uniform current distribution results in non-uniform utilization of active materials, reducing energy density, and likely also accelerating degradation of the Li-ion cell. Future research on diagnosing and improving current density uniformity in large format Li-ion batteries that enable vehicle- and grid-energy storage is highly warranted. (C) 2013 The Electrochemical Society. All rights reserved.