Enhanced electrochemical kinetics and three dimensional architecture lithium iron phosphate/carbon nanotubes nanocomposites for high rate lithium-ion batteries

Abstract

Three-dimensional architecture lithium –iron phosphate (LiFePO4)/carbon nanotubes (CNTs) nanocomposites with outstanding high-rate performances are synthesized by using a combination of in situ microwave plasma chemical vapor deposition (MPCVD) and co-precipitation methods. A stainless-steel mesh is adopted as the green catalyst for the in situ controllable growth of CNTs. Highly conductive and uniformly dispersed CNTs weave an effective three-dimensional (3D) conductive network, each isolate active LiFePO4 nanoparticle is fully wrapped and connected by the CNTs. The optimized electrode of LiFePO4/CNTs nanocomposites deliverer a high initial discharge capacity of 168.7 mAh g−1 at 0.1 C. Amazingly, the discharge capacities can reach 126.1, 111.2, 99.5 and 71.3 mAh g−1 even at high rates of 10 C, 20 C, 30 C and 50 C. The LiFePO4/CNTs nanocomposite displayd an excellent electrochemical performance, such as ultrahigh cyclic stability, extraordinary rate capability and smaller capacity fading at high current densities, which can be ascribed to the synergistic effects of the highly 3D CNTs conductive network and the shorter lithium ion diffusion path in the LiFePO4 nanoparticles. The electrochemical kinetics demonstrate that the insertion process was the rate-determining step at low current densities, while the transports of charges from their reservoirs towards the active particles became prevailing at high current densities. The brilliant high-rate performance of LiFePO4/CNTs nanocomposites can be ascribe that the open and highly conductive network established by CNTs allows a much more efficient ionic and electronic conduction.