Lithiation and delithiation behavior of sodium lithium titanate anode

Na 2 Li 2 Ti 6 O 14 is synthesized by a simple solid state method between 500 and 900   °C. It is found that pure Na 2 Li 2 Ti 6 O 14 is only formed at 800   °C or above. The tap density of as-prepared Na 2 Li 2 Ti 6 O 14 is about 1.52   g   cm −3 . Particle morphology analysis shows that the size of Na 2 Li 2 Ti 6 O 14 gradually increases with the increase of sintering temperature. Calcined at 900   °C, Na 2 Li 2 Ti 6 O 14 shows slight particle aggregation and melting. As a result, Na 2 Li 2 Ti 6 O 14 formed at 800   °C reveals higher electrochemical activity than the sample obtained at 900   °C. Therefore, the suitable preparation temperature for Na 2 Li 2 Ti 6 O 14 by solid state reaction is 800   °C. Charge–discharge results show that Na 2 Li 2 Ti 6 O 14 prepared at 800   °C can deliver a reversible capacity of 89.9   mAh   g −1 at 100   mA g −1 , 81.3   mAh   g −1 at 200   mA   g −1 , 75.2   mAh   g −1 at 300   mA   g −1 , 69.6   mAh   g −1 at 400   mA   g −1 and 65.5   mAh   g −1 at 500   mA   g −1 . Besides, the lithium storage mechanism in Na 2 Li 2 Ti 6 O 14 is also studied by various in-situ and ex-situ methods, which prove that the structural evolution is highly reversible for Na 2 Li 2 Ti 6 O 14 during lithiation/delithiation process.