Oxygen-deficient Nb2O5-x decorated MCMB anode with much enhanced rate and cycle performances for Li-ion batteries

Abstract

Nanosized oxygen-deficient orthorhombic niobium pentoxide (Nb2O5-x) that possess high electronic conductivity and stable cycle performance for Li storage are uniformly deposited on the surface of mesophase carbon microspheres (MCMB), which as a whole exhibits very encouraging electrochemical Li ion storage performance, including a high specific capacity of 107 mAh g−1 at 10C (1C = 372 mA g−1) and a high capacity retention of 85.4 % after 300 cycles at 3C in the optimized case. The Li+ diffusion coefficient of the composite anode as determined by the potentiostatic intermittent titration technique (PITT) is obviously improved as compared to that of pristine MCMB. Ex situ X-ray diffraction characterizations confirm the phase transformation from orthorhombic Nb2O5-x to amorphous LiyNb2O5-x accompanied by the formation of NbO through a conversion reaction in the first lithiation process. The ultrafast Li+ diffusion within the amorphous LiyNb2O5-x as well as the current-sharing effect of the secondary particles can explain the much enhanced Li ion storage property. The results of this work convincingly demonstrate that designing MCMB/Nb2O5-x composite can be a more practical way to improve the energy and powder densities of Li-ion batteries rather than seeking alternative anode materials with higher capacities.