Conductive Nb25O62 and Nb12O29 anode materials for use in high-performance lithium-ion storage

Abstract

Conductive M–NbV–O compounds are high-capacity, fast-charging, safe and stable anode materials that have potential use in lithium-ion batteries. However, their studies are very limited. Here, we facilely fabricate Nb25O62 (i.e., NbIVNbV24O62) and Nb12O29 (i.e., NbIV2NbV10O29) from high-temperature reduction of Nb2O5 in a mixed H2/Ar atmosphere. Nb25O62 shows a monoclinic shear ReO3 crystal structure with a C2 space group and a structural unit containing a 3 × 4 octahedron-block and 0.5 tetrahedron, while Nb12O29 shows a similar structure with an A2/m space group and a 3 × 4 octahedron-block. Their resulting open crystal structures lead to their large Li+-ion diffusion coefficients. Due to the unpaired 4d electrons in Nb4+, their electronic conductivities are increased by three orders of magnitude in comparison with Nb2O5. First-principles calculations even demonstrate their conductor characteristics. Hence, Nb25O62/Nb12O29 exhibits comprehensively good electrochemical performance, including a significant pseudocapacitive contribution (72.7/79.0% at 1.1 mV s−1), high specific capacity (289/287 mAh g−1 at 0.1 C), high working potential (∼1.69/∼1.72 V vs. Li/Li+), superior rate capability (133/165 mAh g−1 at 10 C) and prominent cyclic stability (only 0.3/14.5% capacity loss over 1000 cycles at 10 C). These findings demonstrate that Nb25O62 and Nb12O29 are promising anode materials for future use in high-performance lithium-ion storage.