Preventing high temperature rise during fast charge/discharge is essential in avoiding thermal runaway and extending battery life. One key aspect of understanding temperature rise is being able to calculate the heat generation accurately. Among the four main sources of heat generation in a Li-ion battery, heat of mixing has often been regarded as insignificant and excluded from modeling. When modeled, it is often done using a Taylor expansion approximation. In this work, we carry out the calculation of the total heat generated from the fundamental equation of the rate of enthalpy change in insertion compounds. Heat generation thus calculated naturally includes irreversible, reversible, and mixing heat. We exclusively calculate the heat of mixing by subtracting the rate of enthalpy change by reaction from the rate of the total enthalpy change. Results show that at high charge/discharge rates, the Taylor expansion approximation is invalid and the heat of mixing thus calculated is erroneous. More importantly, the contribution of heat of mixing in the total heat generated increases significantly with the charge/discharge rate and is as large as 22% for 6C discharge of a cell with NMC cathode. This result suggests that while modeling heat generation and temperature rise at high charge/discharge rates, it is necessary to include heat of mixing and avoid calculating it using the method of Taylor expansion.


Heat of Mixing in Nmc523 Cathode During Fast Charge/discharge

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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