Synthesis and Electrochemical Performance of C-Base-Centered Lepidocrocite-like Titanates for Na-Ion Batteries

Lepidocrocite-like titanate, Na0.9[Ti1.7Li0.3]O4, having a C-base-centered lattice (C-type) is prepared by dehydration of Na0.9[Ti1.7Li0.3]O4·nH2O having a primitive lattice (P-type) and influence of the interlayer water on its electrochemical performance is examined in nonaqueous Na cells. Upon heating up to 350 °C, P-type Na0.9[Ti1.7Li0.3]O4·nH2O transforms into the anhydrous C-type phase as a result of gradual removal of the interlayer water. The C-type Na0.9[Ti1.7Li0.3]O4 delivers reversible capacity of 120 mAh g–1 between 2.0 and 0.1 V vs Na with high Coulombic efficiency at an initial cycle and good capacity retention over 50 cycles. Structural change of the C-type phase during sodiation is investigated by using operando X-ray diffraction measurement.