Synergistic Effect of Dual Phases to Improve Lithium Storage Properties of Nb 2 O 5 .

Niobium pentoxides (Nb 2 O 5 ) present great potential as next-generation anode candidates due to exceptional lithium-ion intercalation kinetics, considerably high capacity, and reasonable redox potential. Although four phases of Nb 2 O 5 including hexagonal, orthorhombic, tetragonal, and monoclinic polymorphs show diverse characteristics in electrochemical performance, stable lifetime, high specific capacity, and fast intercalation properties cannot be delivered simultaneously with a single phase. Herein, this issue is addressed by generating a homogeneous mixture of orthorhombic and monoclinic crystals at the nanoscale. Reversible lithium-ion intercalation/deintercalation of the monoclinic phase is achieved, and exceptional lithium storage sites are created at the interface of the two phases. As a result, electrochemical features of stable lifetime from the orthorhombic phase and high specific performance from the monoclinic phase are harmoniously combined. This dual-phase Nb 2 O 5 /C nanohybrids deliver as high as 380 mA h g -1 (0.01-3.0 V) and 184 mA h g -1 (1.0-3.0 V) after 200 cycles. The essential principle of property enhancement is further confirmed through in situ XRD measurements and DFT calculations. The dual-phase concept can be further applied on electrodes with multiphases to achieve high electrochemical performance.