Mixed-valent Nb boosted the electrochemical performance of K3Nb6P4O26@C anode material for lithium-ion batteries

Abstract

Niobium-based anode materials have good prospects for application in lithium-ion batteries (LIBs) due to the advantages of high specific capacity and high safety. However, the low electronic conductivity poses the main obstacle that limits its performance at present. Here, a mixed-valent niobium based phosphate, K3Nb6P4O26@C (KNPO@C), was designed and prepared as the anode material for LIBs. The mixed-valent Nb in KNPO provides multi-electron electrochemical reactions and presents an electronic conductivity higher than that of a sole Nb5+-based material. In addition, the three-dimensional (3D) channels in the crystal structure of KNPO facilitate the rapid transport of lithium-ions. KNPO@C anode delivers a high specific capacity of 250 mA h g–1 at 0.1 C and an excellent cycling stability was measured with a capacity retention of 60.7 % after 1000 cycles at 2 C. The charge/discharge mechanism of KNPO@C was systematically investigated by ex-situ XRD and ex-situ XPS. The kinetic information obtained from the cyclic voltammetry (CV) suggests that the pseudocapacitance effect also play an important role in the specific capacity. These results demonstrate the potential of KNPO@C as a practical anode material for high-performance LIBs.