Electrochemical performance of sol-gel synthesized NaTi₂(PO₄)₃-carbon composites as aqueous na-ion battery anodes

Aqueous Na-ion based batteries are considered promising candidates for replacing Li-ion technologies, especially in the area of stationary energy storage. Research and development of novel electrode materials remain a central research effort in this field. NASICON-structured NaTi2(PO4)3 phosphate framework has attracted a great deal of attention and remains the most studied negative electrode material for aqueous Na-ion batteries. The active material preparation and carbon composite property tailoring play a critical role in the electrode materials engineering process which governs the performance of an entire electrochemical system. We present a study of a series of aqueous sol-gel synthesized NaTi2(PO4)3 - carbon composites using three different sol-gel approaches and three distinct pyrolysis/calcination strategies. The structural and morphological analysis shows that both the sol-gel route as well as the thermal treatment strategy have significant effects on active material purity and degree of crystallinity as well as the content and properties of the carbonaceous phase. Electrochemical investigations of these composites also show strong effects of the materials structure and carbon matrix morphology on the electrochemical performance and degradation of these materials when employed as aqueous Na-ion battery negative electrodes.