Rational selection of amorphous or crystalline V 2 O 5 cathode for sodium-ion batteries.

Vanadium oxide (V2 O5 ), as a potential positive electrode for sodium ion batteries (SIBs), has attracted considerable attention from researchers. Herein, amorphous and crystalline V2 O5 cathodes on a graphite paper without a binder and conductive additives have been synthesized via facile anodic electrochemical deposition following different heat treatments. Both the amorphous V2 O5 (a-V2 O5 ) cathode and crystalline V2 O5 (c-V2 O5 ) cathode show good rate cycling performance and long cycling life. After five rate cycles, the reversible capacities of both the cathodes were almost unchanged at different current densities from 40 to 5120 mA g-1 . Long cycling tests with 10 000 cycles were carried out and the two cathodes exhibit excellent cycling stability. The c-V2 O5 cathode retains a high specific capacity of 54 mA h g-1 after 10 000 cycles at 2560 mA g-1 and can be charged within 80 s. Interestingly, the a-V2 O5 cathode possesses higher reversible capacities than the c-V2 O5 cathode at low current densities, whereas it is inversed at high current densities. The c-V2 O5 cathode shows faster capacity recovery from 5120 to 40 mA g-1 than the a-V2 O5 cathode. When discharged at 80 mA g-1 (long discharge time of 140 min) and charged at 640 mA g-1 (short charge time of 17 min), the a-V2 O5 cathode shows a higher discharge capacity than its c-V2 O5 counterpart. The different electrochemical performance of a-V2 O5 and c-V2 O5 cathodes during various electrochemical processes can provide a rational selection of amorphous or crystalline V2 O5 cathode materials for SIBs in their practical applications to meet the variable requirements.