Lithium based material such as lithium manganese oxide (LiMn₂O₄) of spinel structure is very promising as a cathode material for secondary Li-ion batteries. This compound has several advantages like: low cost and easy preparation, non-toxicity, high discharge potential (4V vs. lithium metal), a satisfactory capacity, high-energy density, low self-discharge and high thermal stability. In spite of these advantages, LiMn₂O₄ suffers from a capacity fading during charge-discharge cycles, which limits the application in commercial lithium-ion batteries. To reduce this undesired phenomenon many strategies have been applied, as described in our earlier works [1, 2]. Another, less serious drawback of lithium manganese oxide is its modest electronic conductivity. There are several ways of enhance it: i) by doping with high valence ions, ii) introducing metal particles or conducting polymers onto LiMn₂O₄ internal surfaces and iii) the most popular – mixing as-synthesized material with carbon species.

In our studies we used various forms of carbon in order to prepare LiMn₂O₄ composites of good electrochemical performance and electronic conductivity.

In this work we prepared series of LiMn₂O₄/C composites. Firstly, using a modified sol-gel method we obtained xerogels of LiMn₂O₄ from lithium and manganese salts and citric acid as a main chelating agent. The gels were dried at 150ºC and ground in an agate mortar. Then they were heated at 450 – 700ºC for a few hours in air, resulting in pure lithium manganese oxide nanocrystalline powders. In the second step we prepared LiMn₂O₄/C composite using different carbon sources: graphene flakes and acetylene black. LiMn₂O₄ powders and carbon species were either blended in an agate mortar or ball-milled, next pelletized in die set under high pressure.

The crystal structures of all samples were characterized by X-ray powder diffraction (XRD) and Raman spectroscopy. The particle size and morphology were observed by scanning electron microscopy (SEM). Impedance spectroscopy (IS) was used to determine the electrical conductivity vs. temperature. Moreover, the galvanostatic charge-discharge tests were carried out to examine the electrochemical performance of LiMn₂O₄/Carbon composites.

[1] M. Michalska, L. Lipińska, M. Mirkowska, M. Aksienionek, R. Diduszko, M. Wasiucionek: Nanocrystalline lithium-manganese oxide spinels for Li- ion batteries – sol-gel synthesis and characterization of their structure and selected physical properties, Solid State Ionics 188 (2011) 160–164.

[2] Monika Michalska, Ludwika Lipińska, Ryszard Diduszko, Marta Mazurkiewicz, Artur Małolepszy, Leszek Stobiński, Krzysztof J. Kurzydłowski: Chemical syntheses of nanocrystalline lithium manganese oxide spinel, Physica Status Solidi C 8, No. 7–8, 2538–2541 (2011) / DOI 10.1002/pssc.201001195.

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