Soft X-Ray Absorption Spectroscopic Study of a LiNi0.5Mn0.5O2 Cathode During Charge

Published

February 1, 2004

Author(s)

W S. Yoon, Mahalingam Balasubramanian, Xiao-Qing Yang, Ziwen Fu, Daniel A. Fischer, James McBreen

Abstract

Soft X-ray (200 eV to 1000 eV) absorption spectroscopy (XAS) at the O K-edge and the metal L_II, _III-edges, in both the fluorescence yield (FY) and the partial electron yield (PEY) mode, has been used to probe the electronic structure of electrochemically deintercalated Li_l-xNi_0.5Mn_O.5O₂. FY and PEY spectra of the transition metal L_II, _III-edges, indicated that Mn ions remain mostly unchanged in the Mn⁴⁺ state at all levels of charge. However, the Ni FY L-edge spectra show a continuous shift to higher energy during charge, but remain mostly unchanged in the PEY data. The results of the FY data show that the Ni ions in the bulk are oxidized from Ni²⁺ to Ni⁴⁺ during charge. The difference between the surface sensitive PEY data and the bulk sensitive FY data indicates that the surface of Li_l-xNi_O.5Mn_O.5O₂ has a different electronic structure than the bulk. The shift in the O K-edge to lower energies and the development of a shoulder on the low energy side of the first pre-edge peak indicates that the holes compensating the lithium ion deintercalation are located in O 2p states as well as Ni 3d states. These results show that soft x-ray absorption is a powerful technique to study the electronic structure of new battery materials and it provides unique complementary information to that obtained from hard x-ray (above 1000 eV) absorption studies at the transition metal K-edges.

Citation

Journal of the Electrochemical Society

Volume

151

Issue

No. 2

Pub Type

Journals

Keywords

batteries, cathodes, lithium, NEXAFS, soft x-ray

Citation

Yoon, W. , Balasubramanian, M. , Yang, X. , Fu, Z. , Fischer, D. and McBreen, J. (2004), Soft X-Ray Absorption Spectroscopic Study of a LiNi_0.5Mn_0.5O₂ Cathode During Charge, Journal of the Electrochemical Society (Accessed April 25, 2024)