Entropy profile of NCR 18650 cylindrical cell at various states of health

Abstract

Entropy measurement at various states of charge (SOC) is a potential non-destructive tool for characterizing lithium-ion batteries; however, traditional potentiometric methods are time-consuming. To address this, we developed a fast potentiometric method that estimates entropy by employing charging after pulse discharging to partly eliminate voltage relaxation. This method, combined with precise mathematical processing, reduces estimation time by approximately 4.5 times compared to conventional approaches. We validated the method by comparing it with the traditional potentiometric method and applied it to obtain entropy profiles of an NCR 18650 Panasonic battery at various cycle numbers at a 1.5C rate. Additionally, we investigated how entropy changes with variations in the battery's state of health (SOH). The study established coefficients for a mathematical model representing SOC across different SOH, revealing a strong correlation for SOC estimation.

Keywords

• State of health
• State of charge
• Li-ion batteries
• Entropy
• Potentiometry