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Sodium-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.

Sodium-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.

Sodium-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.

We report on the first year of calendar ageing of commercial high‐energy 21700 lithium‐ion cells, varying over eight state of charge (SoC) and three temperature values. Lithium‐nickel‐cobalt‐aluminium oxide (NCA) and graphite with silicon suboxide (Gr‐SiOx) form cathodes and anodes of those cells, respectively. Degradation is fastest for cells at 70–80 % SoC according to monthly electrochemical check‐up tests. Cells kept at 100 % SoC do not show the fastest capacity fade but develop internal short circuits for temperatures T≥40 °C. Degradation is slowest for cells stored close to 0 % SoC at all temperatures. Rates of capacity fade and their temperature dependencies are distinctly different for SoC values below and above 60 %, respectively. Differential voltage analyses, apparent activation energy analysis, and endpoint slippage tracking provide useful insights into the degradation mechanisms and the respective roles of anode and cathode potential. We discuss how reversible losses of lithium might play a role in alleviating the rate of irreversible losses on commercial cells.

We report on a cycle ageing study of commercial NCA/Gr+Si cells, in which reversible capacity fluctuations turn a central experimental finding upside down: an upper voltage limit of 4.1 V seems to cause faster degradation than going all the way to 4.2 V. The underlying effect is the reversible loss of lithium inventory into passive anode overhang areas. We demonstrate how the resulting artefact arises from a combination of slow transport processes and the related time periods spent in specific state-of-charge regions. We propose an alternative visualisation tool to identify and manage such artefacts, often neglected in typical ageing studies.

We demonstrate how insufficient heat transport in environmental chambers compromises the meaningfulness of high-precision charge counting and leads to an underestimation of lithium plating in fast-charged lithium-ion batteries. Direct-contact liquid cooling of cylindrical cells excludes temperature fluctuations observed in thermal chambers and restricts self-heating to 2 K in comparison to the 14 K in thermal chambers, under 1.5 C-rate cycling. Our thermal-electrochemical model replicated well the experimental results. For high-precision coulometric studies to be meaningful and more comparable across different laboratories, especially for large-format and high-power cells, direct-contact cooling in thermal baths must become the new standard.

Despite the constancy of all controllable experimental parameters, most natural and artificial oscillators are known to slowly evolve over time. In electrochemical systems, this spontaneous evolution has been ascribed to the surface deactivation that gently drives the system and acts a bifurcation parameter. We investigate the effect of temperature on the electro-oxidation of methanol on platinum, with focus on the potential oscillations and its spontaneous temporal evolution. The study was performed at comparable applied currents (normalized with respect to the oscillatory window) at nine temperatures between 10 °C and 50 °C, in acidic media, and oscillations were not observed at 50 °C. The main results were discussed in connection with voltammetric data, which were deconvoluted into three regions according to the electrode potential. While the frequency of potential oscillations followed a regular Arrhenius-like dependence, the size of the oscillatory window was found to remain nearly unaffected by temperature. From the mechanistic point-of-view, these dependencies were attributed to the existence of more than one Langmuir–Hinshelwood (LH) step that consumes adsorbed oxygenated species. This fact was corroborated by voltammetric data. The relative magnitude of the activation energies of the LH processes were estimated as higher than that of the deactivation process, as previously suggested.

The electrooxidation of small organic molecules such as formaldehyde, formic acid, methanol, ethanol, ethylene glycol, glycerol, and so on is relevant to interconversion between chemical and electrical energies. Although these have considerably low thermodynamic potentials compared to hydrogen, the oxidation process generally demands high overpotentials because of the ubiquitous formation of surface‐blocking carbonaceous species. The occurrence of parallel pathways and the formation of stable soluble by‐products also contribute to the poor utilization of all electrons involved in the oxidation process. Thecomplex kinetics found in these systems can also result in nonlinear manifestations such as autocatalysis and oscillatory dynamics. Besides the considerable amount of earlier experimental reports, only recently has some understanding of the chemistry underlying the dynamics been achieved. Moreover, a number of interesting and unexpected behaviors have been observed under oscillatory regime. In this chapter, we briefly review the recent advances on the oscillatory electrooxidation of small organic molecules, with emphasis on (a) the general phenomenology, (b) the use ofin situ andonline approaches, (c) the effect of temperature, and (d) the oscillations on modified surfaces. Moreover, some implications of nonlinearities in low temperature fuel cells are also discussed.