Oxygen vacancies-enriched sub-7 nm cross-linked Bi2.88Fe5O12- nanoparticles anchored MXene for electrochemical energy storage with high volumetric performances

To improve the structure stability and accelerate electrochemical reaction kinetics, oxygen vacancies-enriched sub-7 nm Bi2.88Fe5O12-x nanoparticles with high electrochemical activity have been elaborately anchored on two-dimensional MXene nanosheets through a facile electrostatic assembly approach for electrochemical energy storage. MXene nanosheets could not only effectively buffer the serious volume change of Bi2.88Fe5O12-x nanoparticles but also facilitate fast electron transfer as a flexible, well-conductive but robust substrate in the fast charge/discharge processes. Owing to the three-dimensional distinct structure and the strong synergistic effects between MXene and Bi2.88Fe5O12-x nanoparticles, the obtained composite exhibits impressive electrochemical performances. The composite electrode possesses high gravimetric specific capacity of 176 mAh g−1 with ultrahigh volumetric specific capacity of 476 mAh cm−3 at 0.5 A g−1 in an aqueous electrolyte, superior to those of the so-far reported Bi2O3-based electrode materials. In addition, our fabricated asymmetric device displays a high volumetric energy density of 177 Wh L−1 and remarkable cycling performance with 93.3% retention ratio after 10,000 cycles. Moreover, the resultant MXene/Bi2.88Fe5O12-x composite presents high reversible specific capacity of 805 mAh g−1 for Li-ion storage, corresponding to the volumetric specific capacity of 2176 mAh cm−‍3.