CT scans of 1k lithium-ion batteries show quality risks in inexpensive cells

Summary

Billions of 18650 lithium-ion cells move quietly into daily life each year, powering everything from toothbrushes and power tools to e-bikes and electric vehicles. All these batteries share the same 18 mm by 65 mm can, but their simple cylindrical packaging conceals the internal jelly roll structure that will ultimately decide how a cell behaves over time. In an increasingly electrified world, cell quality is critical. Every rechargeable device carries a small but real hazard, and when multiplied across billions of gadgets and the numerous cells inside many of them, that risk accumulates. Battery fires and explosions are serious events that cause injuries, fatalities, and substantial property damage.Lumafield set out to measure the quality of batteries from different sources, and we’re publishing the results today in the Battery Quality Report. We CT-scanned and automatically analyzed 1,054 individual cells drawn from ten brands that ranged from established OEMs to rewraps and low-cost marketplace labels. This allowed us to look beyond advertised specifications, measuring the internal geometries that impact performance, degradation, and the risk of internal shorts. Two key quality features anchor the study: anode overhang (AOH) and edge alignment. In liquid-electrolyte lithium-ion cells, electrode misalignment is a known trigger for lithium plating. Plating promotes dendrite growth, which can potentially degrade performance and create internal shorts that escalate into thermal runaway.Across the dataset, the contrasts were clear. Low-cost and counterfeit lots exhibited 7x lower anode-overhang quality relative to OEM cells, along with 50% worse edge alignment. Variability told the broader story: a few brands posted acceptable medians but featured wide distributions with considerable outliers, the signature of weak process control. Most concerning, negative AOH, also known as cathode overhang, appeared in 33 of the 1,054 cells we scanned. This defect significantly rai...