Abstract:

Layered lithium nickel-cobalt-manganese oxides (NCM) have been highlighted as advanced cathode materials for lithium-ion batteries (LIBs); however, their low interfacial stability must be overcome to ensure stable cycling performance of the cell. In this work, we propose a one-step surface modification method that uses a task-specific precursor, N,N,N,N-tetraethylsulfamide (NTESA), to improve interfacial stability of Ni-rich NCM cathode materials. The unstable surface properties of Ni-rich NCM cathode material are improved by embedding an artificial cathode-electrolyte interphase (CEI) layer on the cathode surface by heat treatment of the Ni-rich NCM cathode material with an NTESA precursor at low temperature. Our material analyses indicate that this approach allows the formation of amine- and sulfone-functionalized CEI layers on the surface of Ni-rich NCM cathode material without changing the layered structure of the cathode material. NTESA-functionalized Ni-rich NCM cathode materials exhibit improved cycling retention after 100 cycles: for example, a cell cycled with a 3.0 NTESA-modified NCM811 cathode presents the highest retention ratio of 88.3 %, whereas a cell cycled with a non-functionalized NCM811 cathode suffers from rapid fading of the cycling performance (68.4 %). Our additional SEM, XPS, and EIS analyses indicate that electrolyte decomposition is suppressed during electrochemical cycling, thereby leading to smaller increases in the internal resistances. ICP-MS analyses of the cycled anodes also indicate that the NTESA-based artificial CEI layer inhibits the dissolution of transition metal components from the Ni-rich NCM cathode materials, thereby contributing to an improved overall electrochemical performance of the cell.

Key words: Lithium-ion battery, Cathode, Cathode-electrolyte interphase, N,N,N,N-Tetraethylsulfamide, Electrochemical performance