A systematic study of kinetics in mesocarbon microbeads anodes in presence of nano-conductive additives

Abstract

Nano-conductive additives in composite electrodes play a significant role in influencing the electrochemical performance of the carbon anode in Li-ion batteries. These additives with a high electronic conductivity lead to the formation of a uniform solid-electrolyte interfacial layer, improved cycle life, and rate capability. In this work, the parameters that lead to such a performance improvement, namely the kinetic and transport properties, are carefully studied with carbon black (CB), carbon nanotubes (CNT) and a mixture of the two as conductive additives in mesocarbon microbeads (MCMB) anode. Experimental measurements indicate that the electrochemical reaction rate is controlled by interfacial kinetics up to moderately high C-rate (<6C). Though nano-additives do not affect the solid phase diffusivity, the diffusion of Li-ion is considerably influenced by stages and their coexistence that is revealed through X-ray diffraction of cells at different depths of discharge. Using electrochemical impedance spectroscopy of half-cells cycled at different temperatures, the activation energy for charge transfer reaction and activation energy for SEI layer diffusion are estimated. The results exhibit an improvement in electron transfer and an ionically conducting SEI layer with the use of a mixture of CB and CNT as conductive additives. It is expected that the estimated kinetic and transport parameters and their temperature dependence for the additives under consideration will be of tremendous utility in the thermal, electrochemical, or aging modeling of batteries employing MCMB as anode material.