A chemically bonded NaTi2(PO4)3/rGO microsphere composite as a high-rate insertion anode for sodium-ion capacitorsElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ta05252a

We report on the synthesis of a high rate NaTi 2 (PO 4 ) 3 /graphene composite for use as an anode material for high power Na-ion hybrid capacitors with the following characteristics; (1) reduction of the particle size of NaTi 2 (PO 4 ) 3 to the nanometer scale in order to reduce the Na + ion diffusion length, (2) chemical bonding between NaTi 2 (PO 4 ) 3 nanoparticles and graphene in order to improve electrical conductivity, and (3) interconnected nanoporous structures in order to allow easy access of Na + ions to NaTi 2 (PO 4 ) 3 . For this, the NaTi 2 (PO 4 ) 3 /rGO microsphere composite was prepared via a facile spray drying method using a solution mixture of graphene oxide, NaH 2 PO 4 ·2H 2 O, Ti(OC 2 H 5 ) 4 and NH 4 H 2 (PO 4 ) 3 , in which all the components of the titanium were present as ionic species in order to facilitate the chemical bonding between NaTi 2 (PO 4 ) 3 and rGO in the composite. The NaTi 2 (PO 4 ) 3 /rGO microsphere composite had a Ti-O-C bond between NaTi 2 (PO 4 ) 3 nanoparticles (