A thermodynamic study of Li-Al-O system and application to the cathode materials for lithium-ion batteries

Petronela Gotcu-Freis, C. Ziebert, H.J. Seifert

Karlsruhe Institute of Technology (KIT)

Institute for Applied Materials – Applied Materials Physics (IAM-AWP)

Lithium aluminate compounds became of interest among ceramic materials, with application in various areas of electrochemical energy storage and conversion. Three major lithium-aluminium based oxide compounds are known: Li₅AlO₄, LiAlO₂ and LiAl₅O₈. Extensive studies have been earlier carried on LiAlO₂ as an additive for the commercially in use but with high costs limitations LiCoO₂ cathode material. It has been shown [1] that the solid solution of LiAlO₂ with various lithiated transition-metal oxides can raise the cell voltage and cathode energy density. Such compounds like Li_xAl_yCo_1-yO₂ and further LiAlO₂ doped with Mn⁴⁺, Fe³⁺ and/or Ni³⁺ transition metal ions [2,3] make LiAlO₂ attractive as a constituent of intercalation electrodes.

The available information on the Li₅AlO₄ and LiAl₅O₈ compounds is limited and their applications have been very little explored. Thus, for a comprehensive understanding of the behaviour of active materials containing Li(M,Al)O₂ and, furthermore, higher order oxides such as Li(M,Al)₂O₄ spinels (with M=Co, Mn, Fe and/or Ni), the evaluation of the constituent systems and phase chemistry needs to be performed.

This study was focused on the Li-Al-O system with emphasis on the phase relations and thermodynamic properties of the relevant compounds. Lithium aluminate sample have been prepared by conventional solid-state reaction route and characterised by thermogravimetry and X-ray powder diffraction method. Heat capacities of individual ternary oxides were measured by differential scanning calorimetry in the wide temperature range from 173 to 1723 K. The results were compared with the available experimental data, restricted to a smaller temperature range and combined with the assessment of the Li-Al-O system using the CALPHAD method.

In order to investigate the battery performance, several Al-doped electrodes have been prepared and, subsequently, test coin cells have been assembled. Electrochemical and calorimetric measurements on these coin cells have been performed using an Isothermal Battery Calorimeter.

[1] G. Ceder, Y.-M. Chiang, D.R. Sadoway, M.K. Aydinol, Y.-I. Jang, B. Huang Nature 392 (1998) 694.

[2] Y.I. Jang, B. Huang, Y.-M. Chiang, D.R. Sadoway Electrochemical and Solid-State Letters 1 (1998) 13-16.

[3] R. Stoyanova, A.-L. Barra, M. Yoncheva, E. Kuzmanova, E. Zhecheva Dalton Transactions 40 (2011) 9106-9115.