Electrochemical Analysis and Interfacial Stability of Carbon-Overlay LiNi0.5Mn­1.5O4 Cathode Material for High Potential Lithium Ion Battery

Recently, researches in lithium ion battery have focused on interfacial properties of various cathode materials. The interfacial reaction on the electrode material greatly dominates its electrochemical performances and thermal stability, especially manganese-type spinels. The deteriorated cyclability of LiNi_0.5Mn­_1.5O₄cathode at elevated temperature greatly hinders its realistic applications. One of the reasons is that the high surface reactivity with the electrolyte at an ultimate operating voltage around 4.7V, associating with the dissolution of Mn and the formation of SEI layer.

A proper SEI-layer can not only facilitate lithium intercalations but also provides a good protection from the undesired electrolyte invasion. This study demonstrates the carbon-overlay on the surface of LiNi_0.5Mn­_1.5O₄ electrode through atmosphere-controlled sputter techniques. The advantage of sputtered carbon layer on the electrode surface is without the degrading of pristine spinel structure. The carbon-overlay with the appropriated thickness was found to extend the cycle life and suppress the swelling behavior of LiNi_0.5Mn­_1.5O₄ cathode material. The essential benefits of carbon-overlay is to stable the SEI layer on LiNi_0.5Mn_1.5O₄ cathodes, retarding the severe capacity decay at elevated temperatures. Charge transfer kinetics and failure mechanisms involving the high-voltage oxidation and high temperature degradation are also detailed discussed.