Why is resistance mismatch important in battery pack assembly?

Current distribution within parallel-connected cells is typically not monitored in commercial battery packs in order to reduce battery management system complexity and cost. This means that the effect of internal resistance mismatch must be quantified in order to assess the importance of this consideration in battery pack assembly.

How important is resistance matching in battery packs?

We demonstrate the importance of resistance matching in battery packs. At 4.5C charge and discharge, 20% resistance mismatch reduces lifetime by 40%. We quantitatively explain experimental results using a model of SEI formation. Resistance mismatch causes uneven current sharing.

Do lithium ion cells match internal resistance?

Here we present experimental and modeling results demonstrating that, when lithium ion cells are connected in parallel and cycled at high rate, matching of internal resistance is important in ensuring long cycle life of the battery pack.

How are internal and external batteries benchmarked?

Thereafter, benchmarking of internal and external batteries is performed by using the functions as guidelines, resulting in a variety of design solutions. The design solutions are assessed from an assembly, disassembly and modularity point of view to establish what solutions are of interest.

Why do pack assemblers sorted and binning by internal resistance?

Sorting and binning by internal resistance is beneficial for pack assemblers to better control the charge/discharge profiles that their cells will experience, reducing the probability of exposure to very high C rates and thus increasing average battery life. There are two obvious areas where further experiments would be very valuable.

How do you measure internal resistance of lithium-ion batteries?

Internal resistance was measured at 50% state of charge (SOC) with a 15 s DC pulse of 40 A (17C). While there is no commonly accepted standard for measuring the internal resistance of lithium-ion batteries, we chose this current and time profile because it is relevant to the duty cycle seen by these cells in hybrid vehicles and power tools.