Charge transfer through interfaces in metal-ion intercalation systems

Advantages of a Solid Solution over Biphasic Intercalation for Vanadium-Based Polyanion Cathodes in Na-Ion Batteries

“…A decrease in temperature leads to a significant increase in the charge transfer resistance, resulting in apparent activation energies of 53 ± 5 kJ mol –1 for the NaVPO 4 F material and 35 ± 3 kJ mol –1 for Na 3 V 2 (PO 4 ) 2 F 3 (Figure e,f). This high value of the interfacial charge transfer activation energy for the NaVPO 4 F material is close to the values of 50–60 kJ mol –1 , typically demonstrated by high voltage Li-ion cathodes and graphite anodes in Li-ion cells . The hindered surface reaction explains a more significant effect of lowering the temperature on the average discharge potential of NaVPO 4 F.…”

“…NaVPO 4 F shows a more pronounced drop of the discharge potential both at high rates and lower temperatures compared to Na 3 V 2 (PO 4 ) 2 F 3 (Figure ), although the latter exhibits an additional hysteretic feature due to the nucleation barrier. For the NaVPO 4 F material, the vertical downward shift of the discharge curves should be mainly related to the ohmic and charge transfer overpotentials . To quantify these contributions for the two materials, we performed temperature-dependent electrochemical impedance spectroscopy (EIS) measurements.…”

“…This high value of the interfacial charge transfer activation energy for the NaVPO 4 F material is close to the values of 50−60 kJ mol −1 , typically demonstrated by high voltage Li-ion cathodes and graphite anodes in Li-ion cells. 15 The hindered surface reaction explains a more significant effect of lowering the temperature on the average discharge potential of NaVPO 4 F.…”

“…For the NaVPO 4 F material, the vertical downward shift of the discharge curves should be mainly related to the ohmic and charge transfer overpotentials. 15 To quantify these contributions for the two materials, we performed temperature-dependent electrochemical impedance spectroscopy (EIS) measurements.…”

“…The number of possible rate-limiting steps increases with addressing higher technological levels, while the corresponding limitations remain poorly understood and commonly misinterpreted even at the level of a single particle of an MIB material . Polarization effects, which appear at high charge/discharge rates at room temperature and already at low charge/discharge rates at low temperatures, originate from the same sources of kinetic limitations: slow transport of ions in the electrolyte and the pores of composite electrodes with high tortuosity (ohmic polarization and concentration polarization in the porous medium), slow charge transfer at the electrode/electrolyte interface, , which causes the overpotential buildup (translating into continuous solvent oxidation and detrimental Li or Na plating at the carbonaceous anode at high charge rates and/or at low temperatures), polarization due to the slow diffusion/propagation of phase boundaries in the primary particles of the electrode materials, associated with mechanical stresses induced by steep concentration gradients inside the active materials, which lead to fracture, fatigue issues, and performance decay . The degradation mechanisms and patterns under low-temperature conditions , and at high charge/discharge rates , are, however, different, which again requires careful analysis and material-specific solutions to achieve satisfactory performance at extreme limits of LIBs and SIBs operation.…”