Sulphur Substitution As an Effective Way to Promote the Structural and Electrochemical Performance of the LiMn2O4 Cathode Material

The lithium-ion batteries are considered as the most dominant technology in the field of energy storage due to their high energy density [1]. Since they were introduced into market, the application targets have expanded from small portable devices to large-scale applications including hybrid electric vehicles (HEV), electric vehicles (EV) and stationary energy storage systems [2,3]. Lithium manganese oxide spinel has been recognized as a potential alternative cathode material. In comparison with LiCoO₂, LiNiO₂ and related systems, LiMn₂O₄ spinel possesses many advantages, e.g. high abundance, non-toxicity, low cost and great safety characteristics [4]. Nevertheless, it is well known that stoichiometric lithium manganese spinel suffers from significant capacity fade during the electrochemical cycling which is generally attributed to structural changes caused by Jahn Teller distortion of Mn³⁺ ions [5]. One of the various approaches to achieve better structural stability and hence, improve capacity retention is modification of oxygen sublattice in the LiMn₂O₄spinel by partial substitution with sulphur [6].

The aim of this work was to investigate how sulphur substitution affect the structural and electrochemical properties of LiMn₂O_4-yS_yspinel materials.

Nanosized LiMn₂O_4-yS_y (y = 0 or 0.01) spinel materials were obtained by a modified sol-gel method based on the hydrolysis and condensation processes. The prepared Li-Mn-O-S spinel systems were investigated with regard to the physicochemical properties using X-ray powder diffraction (XRD), elemental analysis (EA), nuclear magnetic resonance (NMR), low-temperature nitrogen adsorption-desorption measurements (N₂-BET), differential scanning calorimetry (DSC) and electrical conductivity (EC) studies. The electrochemical performance of Li/Li⁺/LiMn₂O_4-yS_ycells was examined by galvanostatic charge/discharge tests (CELL TEST) and electrochemical impedance spectroscopy (EIS).

It was established that the introduction of a small amount of sulphur leads to the stabilization of the spinel structure and consequently, the enhancement of the cycling behavior what confirmed that sulphur substitution is an efficient way to advance the structural and electrochemical properties of the LiMn₂O₄spinel.

References:

[1] J. M. Tarascon, M. Armand, Nature 414 (2001) 359-367.

[2] K. Amine, J. Liu, I. Belharouak, S. H. Kang, I. Bloom, D. Vissers, G. Henriksen, Journal of Power Sources 146 (2005) 111-115.

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[4] J. W. Fergus, Journal of Power Sources 195 (2010) 939-954.

[5] L. Yang, M. Takahashi, B. Wang, Electrochimica Acta 51 (2006) 3228-3234.

[6] M. Molenda, R. Dziembaj, D. Majda, M. Dudek, Solid State Ionics 176 (2005) 1705-1709.