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A sodium titanate-carbon (Na 2 Ti 3 O 7 /C) composite as an anode material for sodium-ion batteries (SIBs) is successfully synthesized via a moderate method (500 °C). It can deliver charge capacities of 161 mA h g −1 and 91 mA h g −1 at current densities of 0.05 C and 10 C, respectively. The material can be cycled at 0.2 C for 400 cycles without capacity or voltage decay. This low cost and environmentally friendly Na 2 Ti 3 O 7 /C exhibits excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

Polycrystalline sample of sodium titanium oxide Na 2 Ti 4 O 9 with the tunnel-type structure was prepared by topotactic sodium extraction in air atmosphere from the as prepared Na 3 Ti 4 O 9 sample. The starting Na 3 Ti 4 O 9 compound was synthesized by solid state reaction at 1273 K in Ar atmosphere. The completeness of oxidation reaction from Na 3 Ti 4 O 9 to Na 2 Ti 4 O 9 was monitored by the change in color from dark blue to white, and was also confirmed by the Rietveld refinement using the powder X-ray diffraction data. The sodium deficient Na 2 Ti 4 O 9 maintained the original Na 2.08 Ti 4 O 9 -type tunnel structure and had the monoclinic crystal system, space group C 2 /m , and the lattice parameters of a = 23.1698(3) Å, b = 2.9406(1) Å, c = 10.6038(2) Å, β = 102.422(3)°, and V = 705.57(2) Å 3 . The electrochemical measurements of thus obtained Na 2 Ti 4 O 9 sample showed the reversible sodium insertion and extraction reactions at 1.1 V, 1.5 V, and 1.8 V vs. Na/Na + , and reversible lithium insertion and extraction reactions at around 1.4 V, 1.8 V, and 2.0 V vs. Li/Li + . The reversible capacity for the lithium cell was achieved to be 104 mAh g −1 at the 100th cycle. [ABSTRACT FROM AUTHOR]