Current sharing in parallel cell batteries cycled at high C rates

The high combined power and energy density of lithium-ion batteries give them great potential for being used as the prime power source for several future naval shipboard pulsed power applications. To meet the power and energy requirements, multiple lithium-ion cells will need to be connected in series and parallel. The number of cells needed will depend on the voltage, capacity, and current limit of the individual cells used. The simplest way of connecting multiple cells in parallel is to tie all of the positive terminals together and all of the negative terminals together, creating a new array of cells that can be treated as a single cell within the battery. In this configuration, a single battery management system (BMS) can be used and though this configuration is simpler and more cost effective, it makes it impossible to monitor the individual cells within each parallel array. Any impedance mismatches among a parallel array of cells introduces the possibility for current imbalances to occur. Significant current imbalance could negatively impact the battery's lifetime as well as its safety. The study performed here aimed at measuring the current imbalance present in a battery that has thirty cells connected in parallel (1S/30P) when it is cycled in a pulsed manner at high discharge rates. The current balance observed across two different rates is being characterized and the possible impact it has on battery performance and lifetime is being evaluated. A novel test bed with individual cell diagnostics has been developed that will be discussed along with the methodology behind the research, and the results collected to date.