Sodiation of hard carbon: how separating enthalpy and entropy contributions can find transitions hidden in the voltage profile

Chemphyschem. 2021 Dec 3. doi: 10.1002/cphc.202100748. Online ahead of print.ABSTRACTSodium-ion batteries (NIBs) utilise 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 characterise 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 optimise 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.PMID:34859948 | DOI:10.1002/cphc.202100748

Source: Chemphyschem - December 3, 2021 Category: Chemistry Authors: Michael Mercer Sam Affleck Edgardo Maximiliano Gavilan-Arriazu Alana Aragon Zulke Philip A Maughan Shivam Trivedi Maximilian Fichtner Anji Reddy Munnangi Ezequiel P M Leiva Harry Ernst Hoster Source Type: research