Not Worth a Nickel! A Nickel Metal Hydride Battery Failure Investigation

During service, an energetic internal event in a nickel-metal hydride battery cell resulted in the failure of the product powered by the battery and the battery itself. An investigation was launched to evaluate the failure event and determine root cause. Based on background information provided and known literature on battery failures, hypotheses for various failure modes were formed. As part of testing the hypotheses, a wide array of tools and techniques was utilized, including:

• Visual examination of exemplar and subject batteries was performed that involved the use of optical microscopy, X-ray radiography, and computed tomography (CT) imaging.
• Evaluation of the crystalline phases of the electrochemical active material was performed by X-ray diffraction (XRD).
• Performance testing of exemplar batteries to characterize their charge/discharge behavior.

The data collected from the testing was analyzed and used to conclusively determine the main failure mode of the subject battery as well as all contributory factors leading to the failure event.

During this presentation, the methodology used to diagnose the failure mode and a review of battery materials and chemistry will be discussed.