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Sodium-ion batteries are a technology rapidly approaching widespread adoption, so studying the thermal stability and safety of their components is a pressing issue. In this work, we employed differential scanning calorimetry (DSC) and ex situ powder X-ray diffraction to study the thermal stability of several types of sodium-ion electrolytes (NaClO4 and NaPF6 solutions in PC, EC, DEC, and their mixtures) and various cathode and anode materials (Na3V2(PO4)3, Na3(VO)2(PO4)2F, β-NaVP2O7, and hard carbon) in combination with electrolytes. The obtained results indicate, first, the satisfactory thermal stability of liquid Na-ion electrolytes, which start to decompose only at 270~300 °C. Second, we observed that charged vanadium-based polyanionic cathodes, which appear to be very stable in the "dry" state, demonstrate an increase in decomposition enthalpy and a shift of the DSC peaks to lower temperatures when in contact with 1 M NaPF6 in the EC:DEC solution. However, the greatest thermal effect from the "electrode–electrolyte" interaction is demonstrated by the anode material: the heat of decomposition of the soaked electrode in the charged state is almost 40% higher than the sum of the decomposition enthalpies of the electrolyte and dry electrode separately. [ABSTRACT FROM AUTHOR]

The thermal stability of NASICON-type cathode materials for sodium-ion batteries was studied using differential scanning calorimetry (DSC) and in situ high-temperature powder X-ray diffraction (HTPXRD) applied to the electrodes in a pristine or charged state. Na3V2(PO4)3 and Na4VMn(PO4)3 were analyzed for their peak temperatures and the exothermic effect values of their decomposition processes, as well as the phase transformations that took place upon heating. The obtained results indicate that Mn-substituted cathode material demonstrates much poorer thermal stability in the charged state, although pristine samples of both materials exhibit similar thermal behavior without any DSC peaks or temperature-induced phase transitions in the studied temperature range. The in situ HTPXRD revealed the amorphization of desodiated Na4VMn(PO4)3-based electrodes occurring at 150~250 °C. [ABSTRACT FROM AUTHOR]

Layered O3-type NaMO 2 oxides (M = transition metals) are the main candidates for cathode materials in the actively developing technology of sodium-ion batteries. Nevertheless, despite many years of research, the optimal composition of such materials is still a matter of debate. In this work, we studied the effect of the Fe, Mn and Ni content on the phase composition, structure, thermal stability and electrochemical properties of the cathode materials NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM111), NaNi 0. 5 Fe 0.25 Mn 0.25 O 2 (NFM211), NaNi 0.25 Fe 0.5 Mn 0.25 O 2 (NFM121) and NaNi 0.25 Fe 0.25 Mn 0.5 O 2 (NFM112). All materials demonstrate similar discharge capacity (125–131 mAh·g−1) when cycling in the 1.9–4.0 V vs Na/Na+ potential range. However, only the NFM111 and NFM112 samples show a low increase in charge transfer resistance during cycling and acceptable thermal stability. Low-temperature experiments revealed good capacity retention for the NFM111 electrode material with loss of only ∼20 % of capacity when the temperature drops from +25 to −30°С. Thus, the NFM111 oxide exhibits a balanced combination of the electrochemical properties and, along with manganese-enriched composition, can be considered as a good choice for further development of cathode materials for sodium-ion batteries. [Display omitted] • Influence of the Fe/Mn/Ni ratio on the electrochemical properties of NaMO 2 is studied. • Equimolar and Mn-rich samples demonstrate the best cycling and thermal stability. • Equimolar NaNi 1/3 Fe 1/3 Mn 1/3 O 2 sample exhibits the highest diffusion coefficients. • Equimolar and Mn-rich samples demonstrate the lowest growth in Rct upon cycling. • Equimolar oxide retain up to 80 % of the capacity upon cooling down to −30 °C. [ABSTRACT FROM AUTHOR]