Li3V2(PO4)3 Particles Anchored in Carbon Nanofiber As a Cathode Material for High-Power Lithium Rechargeable Battery

Abstract

Lithium rechargeable battery has been rapidly developed for the applications in portable devices, electric vehicles (EV), and hybrid electric vehicles (HEV) due to their high energy density and durable cycle life. From the viewpoint of electrode, fast lithium ion and electron transport are essential to enhance its electrochemical performance. However, it is quite challenging to improve both properties at the same time, especially for cathode materials. Thus, no matter what we develop for new cathode materials, there have been severe limitations in terms of lithium ion diffusivity and electronic conductivity. Phosphate (PO4)3--based materials have been attracting tremendous interests due to their competitive energy density and remarkable thermal stability. Among these phosphates, monoclinic Li3V2(PO4)3 (LVP) was proposed as a highly promising cathode material, owing to its high operating voltage and very high theoretical capacity of 197 mAh g-1 when all three lithium ions are extracted/inserted between 3.0 and 4.8 V. In particular, its three-dimensional structure framework consisting of slightly distorted VO6 octahedral and PO4 tetrahedral sharing oxygen vertex provides large interstitial space that makes lithium ions capable of moving fast inside the structure. However, just like the other metal phosphates, it shows a limited electron conductivity (10-8 - 10-9 S cm-1), which makes LVP to be difficult for practical applications. Herein, we present a sagacious design of LVP/carbon nanofiber with a distinctive morphology where LVP nanoparticles are anchored in the surface of carbon nanofiber. In general carbon-coated LVP 1D materials, there has been a problem that the carbon coating layer additionally interferes with lithium ion diffusion into LVP bulk. However, in our structure, LVP particles can directly contact with electrolytes leading to an improved lithium ion conductivity. Furthermore, carbon nanofiber can provide fast electron transport along its 1D pathway. As a result, it was demonstrated that this unique structure is favorable for simultaneously maximizing Li ion conductivity and electronic conductivity for great electrochemical improvement of LVP materials. Figure 1