(Invited) Heat Generation in Batteries Under Extreme Fast Charge: A Multi-Scale Perspective
Authors: Santhanagopalan Shriram , Sunderlin Nathaniel , Fink Kae , Saxon Aron , Yang Chuanbo 
Published: February 2020

Lithium-ion batteries are entering the next generation of applications, ranging from wearable micro-watt scale electronics to mega-watt scale stationary installations. Target specifications for batteries have also been re-hashed over the recent years: the energy density (Wh/kg) at the material level, as well as the cell-level volumetric energy density (Wh/l of the cell) have almost tripled in the last 10 years; there are constraints on composition of the cathodes both from technical demands as well as availability of resources; there is an urgent need to drastically reduce charge times of batteries – which in turn has implications for choice of anode material and customizing cell architecture, among other changes. New materials, differences in cell architecture and operating conditions – all these factors contribute to the amount of heat generated within the battery, at various length and time scales.
At the micro-scale, changes to grain-size and orientation have been tied to efficiency losses in transport across the active material.1 Recently, experimental results relating changes in valences of specific transition metal cations to heat signatures of various NMCs have been used to study stability of these cathodes.2,3 These results correlate well with DFT calculations reported previously. At the meso-scale, resolving the micro-structure using tomography and phase-contrast has enabled us to resolve electrode geometries. In turn, these measurements have been used to develop recipes4 for electrodes suitable for fast charging. The meso-scale models also aid development of fabrication techniques such as patterning of the electrodes or developing printed electrodes for niche applications. At our lab, we have used micro-calorimetry to monitor thermal impedances across the interface of cell components. These measurements help isolate material contributions to heat generation within the cell from engineering limitations. At the cell-level, several complimentary approaches5-8 have been presented in the recent years to computing heat and reaction distribution. NREL has also shown experimental results on cell-level calorimetry that corroborate several of the model results.
This presentation will provide an overview of experimental measurement of performance limitations at different length scales and present a few case-studies that emphasize the use of mathematical models to interpret experimental results, as well as explore the implications for battery-design across multiple-length scales.
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