O 7 ) 2 /multi-walled carbon nanotube (MWCNT) composite was fabricated by a solid state reaction and was further used to fabricate a cathode for sodium-ion batteries. The electrochemical behaviors were thoroughly investigated in assembled non-aqueous Na 3.12 Fe 2.44 (P 2 O 7 ) 2 /MWCNT//Na cells, showing higher specific capacity (over 100 mA h g À1 at a rate of 0.15C) and better stable cycle performance than those of the pristine Na 3.12 Fe 2.44 (P 2 O 7 ) 2 -based one. It is noted that with increased charge-discharge cycles, the specific capacity of Na 3.12 Fe 2.44 (P 2 O 7 ) 2 /MWCNT gets close to the theoretical capacity (ca. 117.4 mA h g À1 ). These good performances could be attributed to the incorporated MWCNTs, which improve the conductivity for lower charge transfer resistance and shorten the diffusion length for faster Na + diffusion to access the reaction sites. Through systematic studies of EIS at different states of charge and discharge, it is discovered that R ct decreases with the increase of voltage and reaches a minimum value at redox sites, but R e and D Na + show the opposite trend.Moreover, a full cell test using a carbon black negative electrode also demonstrates good capacity retention up to 50 cycles and a reversible capacity of 145 mA h g À1 with the average operation voltage of 2.8 V.

3D porous interconnected NaVPO4F/C network is fabricated by a hydrothermal method and sintering process. As a Na-ion battery cathode material, it delivers a good electrochemical performance.