Abstract:

In this study, nanoengineered pseudocapacitive electrodes are developed for
superior Na-ion storage. Main aim is to induce defect-driven
pseudocapacitive Na-ion storage in insertion and conversion type anodes.
Hybrid anatase-bronze TiO2 nanosheets composed of Nanocrystallites of 65%
anatase and 35% bronze was developed to enhance the Na-ion storage
performance of TiO2 based anodes. The biphasic TiO2 nanosheets demonstrated
superior Na-ion storage electrochemical performance compared to pure bronze
and anatase TiO2 nanosheet samples. A high specific capacity of 290 mAh/g
was achieved at a current density of 25 mA/g. Hybrid TiO2 anode maintained a
specific capacity of 105 mAh/g even at a high current density of 1 A/g, and
exhibited excellent cycling stability (90% after 2500 cycles) and coulombic
efficiency (100%). Pseudocapacitive Na-ion storage contribution of the
hybrid nanosheets were considerably higher (62%) compared to that of pure
bronze nanosheets (34%). In this case, nanosheet morphology and mesoporous
nature enabled superior Na-ion diffusion and contact with the electrolyte
solution respectively. It is proposed that grain boundaries between (010)
facet exposed bronze phase and (101) facet exposed anatase act as additional
sites for pseudocapacitive Na-ion storage.
Defect rich Co3O4 nanosheets were fabricated for enhanced pseudocapacitance
assisted Na ion storage. When tested as anode materials for Na-ion
batteries, these high aspect ratio nanosheets demonstrated excellent
specific capacities (622 mAh/g at 25mA/g) and rate performances (157mAh/g at
1A/g) compared to Co3O4 nanoparticles. Ultrathin nature and presence of
meso/macro pores are beneficial for superior interfacial charge transfer and
accommodating volume changes during conversion reaction. Superior Na-ion
storage performance of Co3O4 nanosheets is attributed to synergistic effect
of conversion reaction and defect induced pseudocapacitance.