Ship safer, higher-performance lithium-ion products faster with SensLi
SensLi instruments from CAMX Power detect and quantify self-discharge in Li-ion cells, achieving megaohm-range sensitivity in a matter of hours.
What is self-discharge analysis?
Self-discharge analysis measures how quickly a lithium-ion cell loses energy while unused; elevated self-discharge can point to serious underlying defects that may grow worse over time. Left undetected, these issues can lead to degraded battery capacity, reduced service life, or, in rare cases, fire or other catastrophic failure. By identifying problem cells early, self-discharge screening helps cell manufacturers and pack integrators mitigate the risk of damaging field failures.
Self-discharge related to metallic particle contamination in the cell often grows in severity over successive charge/discharge cycles. In extreme cases, the heat created by the self-discharge current initiates a self-accelerating chemical reaction known as thermal runaway.
The SensLi advantage
Cell manufacturers’ quality control for self-discharge typically employs the effective but time-consuming method of leaving cells on the shelf for days or weeks while monitoring any drop in their open-circuit voltage (OCV). The decrease in OCV over this “aging” period is directly related to the cells’ self-discharge.
To increase the sensitivity of an OCV-based self-discharge measurement, the duration of the aging period can simply be increased. But longer aging periods incur significant costs: larger cell storage facilities, more measurement infrastructure, and a slower production pipeline. As such, cell manufacturers necessarily make tradeoffs between sensitivity and cost.
The proprietary cell screening technology (CST) behind SensLi completely rewrites the cost/sensitivity tradeoff for self-discharge analysis, achieving far better sensitivity than OCV-based methods in a fraction of the time.
The difference: kΩ-range sensitivity in days or weeks using OCV monitoring…
…versus MΩ-range sensitivity in hours using SensLi
Source: McCoy, PSC, 2023
Case study: 18650 screening for a high-reliability application
SensLi instruments were used to screen 18,000 2.6 A-h 18650 format cells from a leading manufacturer, with the intent of building an inventory of “known good cells” for a high-reliability application. Upon reviewing the results, more than 1% of the incoming cells—all of which had passed manufacturer quality control—were found to have elevated self-discharge. This represented a change in quality from the previous generation of cells from the same manufacturer. Subsequent long-duration OCV monitoring of the flagged cells validated these findings, with many cells approaching 0% state-of-charge after 18 months and one cell failing via over-discharge. These CST results, among other factors, led the customer to transition to a different cell manufacturer for their application.
SensLi screening results for 18,000 cells (2.6 Ah, 18650 format) as received from a leading manufacturer. More than 1% of these cells exhibited elevated self-discharge, despite having passed manufacturer quality control. (Click to expand)