Synthesis of layered cathode material Li[CoxMn1-x]O-2 from layered double hydroxides precursors

摘要

Cathode materials Li[CoxMn1-x]O-2 for lithium secondary batteries have been prepared by a new route-precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass pectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH center dot H2O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li+ into the lattice, resulting in the formation of layered Li[CoxMn1-x]O-2 with alpha-NaFeO2 structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[CoxMn1-x]O-2, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[CoxMn1-x]O-2 have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAhg(-1) for the layered material Li[Co0.80Mn0.20]O-2. (C) 2007 Published by Elsevier Inc.