Low cost electrochemical energy storage is very much desired for electric grid and transportation. Concerns on cost and availability of lithium are raised for lithium ion battery (LIB) and other Li-chemistry based energy storage technologies, such as Li-Air and Li-S systems. Sodium ion battery (SIB) is considered as an alternative technology, due to the potentially low cost and abundance of sodium^[1]. Yet many key components, including cathode, anode, electrolyte, still require further improvement.

Hard carbon and Sn alloys have shown good performance as anode for SIBs. Intercalation anodes are also desired owing to relatively small volume changes during cycling. Some titanates, such as Na₂Ti₃O₇ and Na₂Ti₆O₁₃ have been reported to have high performance. In this work, we report several new titanate compounds as promising anode material for sodium ion batteries. The compounds are synthesized through solid state reactions. Powder X-ray diffraction (XRD) and refinement were applied to identify and confirm the crystal structure. Electron microscopy was used to study the morphology of the compound and to compare the products with different synthesize treatments. The electrochemical tests showed that ~80 mAh/g reversible capacity can be achieved with good retention for one of the titanates, as shown in Figure 1, for cycling at C/10 rate between 0.01-2.5V. Ex situ and in situ XRD are used to study the structural changes during cycling. The results demonstrated a topological intercalation with small lattice volume change. The influence of synthesis conditions, including temperature, ball mill rate and carbon coating amount were also investigated.

Figure caption:  Figure 1. The electrochemical cycling voltage curves of the titanate at C/10 rate between 0.01 and 2.5V.

[1] S.P.Ong, G. Ceder, Energy Environ. Sci.,2011,4,3680-3688