NASICON-structured NaTi2(PO4)3 has been considered as an outstanding potential cathode material for Na-ion batteries (NIBs) because of its good Na-ion intercalation reversibility and extremely small structural changes during charge/discharge cycling.1 Despite these advantages, NaTi2(PO4)3 suffers from intrinsically poor electronic conductivity, which leads to poor charging/discharging rate performance of NIBs. Up to now, several effective ways have been proposed to improve the electrochemical properties such as specific capacity and cycling stability, including reduction of the particle size to nanoscale, the addition of a surface coating and the synthesis of composite materials with conductive carbons.2
In particular, the composites of NASICON-structured materials with carbonaceous materials such as mesoporous carbon and graphene of reduced graphene oxide (rGO) has been recently proposed to enhance electronic conductivity of the electrode for improving the cycling performance.3 Graphene acts as a template due to its high specific surface area not only to deposite nano-sized metal oxide but also to connect the nano particles along a 2-dimensional conduction path. Furthermore, graphene can provide a void space against the volume changes of the metal oxide particles during lithium ion insertion/extraction process, which can improve the cycling performance. However, previously reported methods to fabricate of these composites require multistep, time-consuming processes, and complicated.4 Moreover, in this multistep method, the sodiation and heat treatment steps unfavorably affect the size, morphology and homogeneity of the resulting NaTi2(PO4)3 particles. Accordingly, their electrochemical properties showed only a marginal improvement compared with the bare NaTi2(PO4)3.
In this study, we have developed a phase-pure NaTi2(PO4)3/rGO nanocomposite through a facile one-pot synthesis based on microwave-assisted solvothermal synthesis, in which rGO was used to selectively heat the substrate to facilitate the preferential precipitation of NaTi2(PO4)3 nanoparticles (30-40 nm). Ti-O-C bonds formed during the synthesis process, which could efficiently transfer the electrons from the NaTi2(PO4)3 nanoparticles to rGO substrates. The strongly bonded NaTi2(PO4)3/rGO nanocomposite prepared in this study exhibited an excellent rate capability and good cyclability as an anode material for SIBs.
References
1. Il Park et al, J Electrochem Soc 2011, 158, A1067.
2. Pang, G. et al, J Mater Chem A 2014, 2, 20659.
3. Li et al,J Electrochem Soc 2014, 161, A1181.
4. Pang, G. et al, Nanoscale 2014, 6, 6328.