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Sodiation Of Hard Carbon: How Separating Enthalpy And Entropy Contributions Can Find Transitions Hidden In The Voltage Profile |
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| Authors: | Dr Michael Peter Mercer Sam Affleck Dr Edgardo Maximiliano Gavilán-Arriazu Dr Alana Aragón Zülke Dr Philip A Maughan Shivam Trivedi Prof Maximilian Fichtner Dr Anji Reddy Munnangi Prof Ezequiel P M Leiva Prof Harry Ernst Hoster |
| Institution: | 1. Department of Chemistry, Lancaster University, Bailrigg, Lancaster, LA1 4YB UK;2. Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, INFIQC, Córdoba, Argentina
Facultad de Matemática, Astronomía y Física, IFEG-CONICET, Universidad Nacional de Córdoba, Córdoba, Argentina;3. Department of Chemistry, Lancaster University, Bailrigg, Lancaster, LA1 4YB UK The Faraday Institution, Quad One, Harwell Science and Innovation Campus, Didcot, UK;4. Helmholtz Institute Ulm (HIU), D-89091 Ulm, Germany;5. Faculty of Science and Engineering, Swansea University, Fabian Way, Swansea, UK;6. Departamento de Química Teórica y Computacional, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, INFIQC, Córdoba, Argentina |
| Abstract: | Sodium-ion batteries (NIBs) utilize cheaper materials than lithium-ion batteries (LIBs) and can thus be used in larger scale applications. The preferred anode material is hard carbon, because sodium cannot be inserted into graphite. We apply experimental entropy profiling (EP), where the cell temperature is changed under open circuit conditions. EP has been used to characterize LIBs; here, we demonstrate the first application of EP to any NIB material. The voltage versus sodiation fraction curves (voltage profiles) of hard carbon lack clear features, consisting only of a slope and a plateau, making it difficult to clarify the structural features of hard carbon that could optimize cell performance. We find additional features through EP that are masked in the voltage profiles. We fit lattice gas models of hard carbon sodiation to experimental EP and system enthalpy, obtaining: 1. a theoretical maximum capacity, 2. interlayer versus pore filled sodium with state of charge. |
| Keywords: | thermodynamics batteries hard carbon sodium-ion entropy |