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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]

Ti 2 Nb 2 O 9 with a tunnel-type structure is considered as a perspective negative electrode material for Li-ion batteries (LIBs) with theoretical capacity of 252 mAh g -1 corresponding to one-electron reduction/oxidation of Ti and Nb, but only ≈160 mAh g -1 has been observed practically. In this work, highly reversible capacity of 200 mAh g -1 with the average (de)lithiation potential of 1.5 V vs Li/Li + is achieved for Ti 2 Nb 2 O 9 with pseudo-2D layered morphology obtained via thermal decomposition of the NH 4 TiNbO 5 intermediate prepared by K + → H + → NH 4 + cation exchange from KTiNbO 5 . Using operando synchrotron powder X-ray diffraction (SXPD), single-phase (de)lithiation mechanism with 4.8% unit cell volume change is observed. Operando X-ray absorption near-edge structure (XANES) experiment revealed simultaneous Ti 4+ /Ti 3+ and Nb 5+ /Nb 4+ reduction/oxidation within the whole voltage range. Li + migration barriers for Ti 2 Nb 2 O 9 along [010] direction derived from density functional theory (DFT) calculations are within the 0.15-0.4 eV range depending on the Li content that is reflected in excellent C-rate capacity retention. Ti 2 Nb 2 O 9 synthesized via the ion-exchange route appears as a strong contender to widely commercialized Ti-based negative electrode material Li 4 Ti 5 O 12 in the next generation of high-performance LIBs.