Nitrogen doped carbon layer of Li2MnSiO4 with enhanced electrochemical performance for lithium ion batteries

Abstract

The nitrogen doped carbon coating layer on the surface of Li2MnSiO4 (Li2MnSiO4/NC) is successfully synthesized by a simple sol-gel process and examined as a cathode in lithium ion batteries. Surface composition and structure analysis confirm that nitrogen is homogeneous incorporated into the carbon layer and dispersed on the surface of Li2MnSiO4 particles, and the nitrogen doping types include contributions of pyridinic nitrogen, pyrrolic nitrogen, and graphitic nitrogen. Compare with undoped Li2MnSiO4/C, the Li2MnSiO4/NC exhibits even better capacity and rate performances. In particular, when the coating layer contains nitrogen with a desirable mass ratio, the specific discharge capacity for the Li2MnSiO4/NC can reach 277.3 mAh g−1 at the rate of 0.1C, corresponding to the capacity retention of 74.4% after 50 cycles. These excellent electrochemical properties are mainly ascribed to the nitrogen doping, which changes the electronic structure of the carbon layer to enhance the electrical conductivity of Li2MnSiO4 cathode, since the higher electronegativity of nitrogen than carbon. More importantly, pyridinic nitrogen and pyrrolic nitrogen play a leading role, which enhances the electronic conductivity as well as graphitic nitrogen but also creates abundant of defects as electrochemical actives to facilitate Li+ rapid migration at the interface.