Formation and operating mechanisms of single-crystalline perovskite NaNbO3 nanocubes/few-layered Nb2CTx MXene hybrids towards Li-ion capacitors

Lithium-ion capacitors (LICs), combining the merits of both lithium-ion batteries and supercapacitors, possess high energy/power density and a long-duration lifespan in one device. However, the dynamic imbalance between the positive and negative electrodes greatly limits their further practical application. Herein, we first fabricate single-crystalline perovskite NaNbO3 nanocubes (S-P-NNO NCs) via a simple hydrothermal alkalization strategy by using the few-layered Nb2CTx MXene (f-Nb2CTx) as a precursor, and further assemble the resultant S-P-NNO NCs with f-Nb(2)CT(x)via a freeze-drying process to fabricate S-P-NNO/f-Nb2CTx hybrids. The in-depth understanding of the formation of the S-P-NNO NCs is reasonably unveiled with comprehensive experiments. Benefiting from the compositional optimization and synergistic effects between S-P-NNO NCs and f-Nb2CTx, the optimized S-P-NNO/f-Nb2CTx nanohybrid exhibits a large reversible capacity of similar to 157 mA h g(-1) at 2.0 A g(-1). The S-P-NNO/f-Nb2CTx based LICs are endowed with an energy density of similar to 56 Wh kg(-1) at an ultrahigh power density of 13 kW kg(-1), along with a long-duration cycle stability (similar to 75% retention after 4000 cycles). The intrinsic Li-storage mechanism of the S-P-NNO/f-Nb2CTx anode is put forward with in/ex situ X-ray diffraction analysis. More meaningfully, the devised synthetic methodology and unique insights here will stimulate the extensive development of novel Nb-based oxides towards next-generation LICs and beyond.

Automated summary

In this study, lithium-ion capacitors based on S-P-NNO/f-Nb2CTx hybrids were developed, demonstrating high energy density and long cycle stability. The formation mechanism of the hybrids was revealed, with the optimized nanohybrid showing excellent electrochemical performance at high power densities.