LiNi sub(0.5)Mn sub(1.5)O sub( 4) high-voltage cathode coated with Li sub(4)Ti sub(5)O sub(12): a hard X-ray photoelectron spectroscopy (HAXPES) study

• Published in: Physical chemistry chemical physics : PCCP Vol. 17; no. 47; pp. 31790 - 31800
• Main Authors: Sachs, Malte, Gellert, Michael, Chen, Min, Drescher, Hans-Jorg, Kachel, Stefan Renato, Zhou, Han, Zugermeier, Malte, Gorgoi, Mihaela, Roling, Bernhard, Gottfried, JMichael
• Format: Journal Article
• Language: English
• Published: 01.11.2015
• Subjects: Cathodes; Coating; Electrolytes; Manganese; Nickel; Photoelectron spectroscopy; Spinel; Titanium
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp03837e

A Li sub(4)Ti sub(5)O sub(12) (LTO) film was coated as buffer layer onto a LiNi sub(0.5)Mn sub(1.5)O sub(4) (LNMO) high-voltage cathode, and after cycling of the cathode in a battery electrolyte, the LTO film was investigated by means of synchrotron radiation based hard X-ray photoelectron spectroscopy (HAXPES). By tuning the photon energy between 2 keV and 6 keV, we obtained non-destructive depth profiles of the coating material with probing depths ranging from 6 nm to 20 nm. The coating was found to be covered by a few nanometers thin surface layer resulting from electrolyte decomposition. This layer consisted predominantly of organic polymers as well as metal fluorides and fluorophosphates. A positive influence of the Li sub(4)Ti sub(5)O sub(12) coating with regard to the size and stability of the surface layer was found. The coating itself consisted of a uniform mixture of Li(i), Ti(iv), Ni(ii) and Mn(iv) oxides that most likely adopted a spinel structure by forming a solid solution of the two spinels LiNi sub(0.5)Mn sub(1.5)O sub(4) and Li sub(4)Ti sub(5)O sub(12) with Li, Mn, Ni and Ti cations mixing on the spinel octahedral sites. The diffusion of Ni and Mn ions into the Li sub(4)Ti sub(5)O sub(12) lattice occurred during the heat treatment when preparing the cathode. The doping of Li sub(4)Ti sub(5)O sub(12) with the open d-shell ions Ni super(2+) (d super(8)) and Mn super(4+) (d super(3)) should increase the electronic conductivity of the coating significantly, as was found in previous studies. The complex signal structure of the Ti 2p, Ni 2p and Mn 2p core levels provides insight into the chemical nature of the transition metal ions.