Heat loss distribution: Impedance and thermal loss analyses in LiFePO4/graphite 18650 electrochemical cell

• Published in: Journal of power sources Vol. 328; pp. 413 - 421
• Main Authors: Balasundaram, Manikandan, Ramar, Vishwanathan, Yap, Christopher, Lu Li, Tay, Andrew A.O., Palani Balaya
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2016
• Subjects: Calorimetry; Impedance; Internal resistance; Irreversible heat; Reversible heat; Thermal loss; Calorimetry; Irreversible heat; Impedance; Internal resistance; Reversible heat; Thermal loss
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2016.08.045

We report here thermal behaviour and various components of heat loss of 18650-type LiFePO4/graphite cell at different testing conditions. In this regard, the total heat generated during charging and discharging processes at various current rates (C) has been quantified in an Accelerating Rate Calorimeter experiment. Irreversible heat generation, which depends on applied current and internal cell resistance, is measured under corresponding charge/discharge conditions using intermittent pulse techniques. On the other hand, reversible heat generation which depends on entropy changes of the electrode materials during the cell reaction is measured from the determination of entropic coefficient at various states of charge/discharge. The contributions of irreversible and reversible heat generation to the total heat generation at both high and low current rates are evaluated. At every state of charge/discharge, the nature of the cell reaction is found to be either exothermic or endothermic which is especially evident at low C rates. In addition, electrochemical impedance spectroscopy measurements are performed on above 18650 cells at various states of charge to determine the components of internal resistance. The findings from the impedance and thermal loss analysis are helpful for understanding the favourable states of charge/discharge for battery operation, and designing better thermal management systems. •Determination of entropic coefficient and its correlation with cell temperature.•Contribution of reversible and irreversible heat losses at various current rates.•Compliance of total heat loss by ARC with sum of component heat losses.•Resolving internal resistance into different components using impedance technique.•Ohmic resistance is found to be the major contribution to internal resistance.