Lithium-Ion Battery State-of-Health Monitor

This innovative technology uses a single-point diagnostic to determine instability of a single lithium-ion battery cell within a rechargeable battery pack.

Researchers have developed a diagnostic tool that tests entire battery packs to determine in real-time if a cell within the pack has suffered damage without the need to individually test each cell separately. A single damaged cell can create an unreliable or even dangerous situation even though the battery pack as a whole exhibits “normal” voltage behavior. NRL’s diagnostic applies a small AC current or voltage to a battery at a specific frequency which is invariant with battery state-of-charge. Changes in the impedance response are indicative of damage or abuse within the cells.

The NRL single-point diagnostic technology can operate as a stand-alone diagnostic or in real-time as part of an online monitoring system. Testing has demonstrated that the diagnostic is sensitive enough to detect a single overcharge event in one cell of a battery pack. Thresholds can be established to indicate relative damage and safety levels of a battery pack, from a unit that has a single cell that is starting to fail up to a unit that is nearing catastrophic failure.

BENEFITS:

• Simple: The single-point impedance diagnostic method can detect damage to individual cells through a single connection to the battery pack; an a priori baseline for an individual unit is not required once a particular make/model of battery has been characterized
• Efficient: The use of a single frequency enables a quick test, the diagnostic can work in real-time, and health can be monitored regardless of the batteries’ state-of-charge
• Sensitive: The NRL battery health monitor can detect an initial overcharge as well as report relative levels of damage from minor impairment to nearly catastrophic failure