The market of lithium-ion batteries develops rapidly. These batteries are commonly used in portable electronic devices, such as: cell phones, notebooks, tablets, ipods, media players, as well as in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), owing to its high energy density and working voltage, long lifecycle, small dimensions and weight. Especially, the last applications require large format batteries and the their safety becomes a key issue.

Lithium manganese oxide (LiMn₂O₄) of spinel structure has been extensively studied as a cathode material for Li-ion batteries. Application of LiMn₂O₄ has several advantages like: low cost, easy preparation, non-toxicity, high potential (4V vs. lithium metal), a satisfactory capacity, high-energy density, low self-discharge and high thermal and structural stability. In spite of these advantages, LiMn₂O₄ suffers from a serious capacity fading during charge-discharge cycles, which is unacceptable in commercial applications. This problem can be caused by several factors: manganese dissolution, electrolyte decomposition at high potentials, the Jahn-Teller distortion at the state of a deep discharge and lattice instability. There are various strategies to improve structural stability of LiMn₂O₄. One of them is a partial substitution of manganese ions by other divalent or trivalent metal elements e.g. Fe, Co, Ni, Al. Another way is to use nonstoichiometric lithium manganese spinel like – Li_1+xMn_2-xO₄. Modifying their surface by ceramic coating is practiced, too. Recently, a new class of safe anode materials – lithium titanium oxide (Li₄Ti₅O₁₂) of the spinel structure is investigated. This compound is very suitable for LiMn₂O₄ used as cathode.

We succeeded in obtaining nanocrystalline compounds of spinel structure by modified sol-gel method. Examples spinels: LiMn₂O₄ (stoichiometric, nonstoichiometric and substituted) [1] and Li₄Ti₅O₁₂ will be showed. The details of sol-gel synthesis will be presented at the Symposium. All mentioned above compounds are safe (resistant to uncontrolled oxidation) and environment friendly.

As-synthesized samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (differential scanning calorimetry DSC and thermogravimetry TGA), Raman spectroscopy. Also the electrochemical properties of synthesized powders were examined. All obtained materials were nanostructured, single phase and exhibited good specific capacity. Some of them showed improved cycle-ability. Application of nanocrystalline electrode materials has many additional advantages: high surface area, new active reactions, decrease the path length for Li ion transport, reduce the specific surface current rate, improved stability, enhanced specific capacity. The modified sol-gel synthesis turned out to be a very effective way for production of the electrode materials for lithium ion batteries.

References

[1] M. Michalska, L. Lipińska, M. Mirkowska, M. Aksienionek, R. Diduszko, M. Wasiucionek, Solid State Ionics 188 (2011) 160-164.

Acknowledgments

This work was supported by The National Centre for Research and Development through the research grant PBS1 (contract no. PBS1/A1/4/2012) and by The National Science Centre through the research grant PRELUDIUM 2 (decision no. DEC-2011/03/N/ST5/04389).

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