In recent years most of the researches on novel electrode materials for Li-ion rechargeable batteries have been concentrated on phosphoolivines and oxides of the spinel structure. There is a significant interest in structural properties of these materials because electrode capacity and battery performance depend mostly on the rate of lithium diffusion and electron transport. Phosphates – olivines have excellent structural stability (strong bonds: P-O), good cycle life, thermal and chemical stability and are safe [1]. Lithium iron phosphates LiFePO₄ have good lithium intercalation properties, high specific stored energy, and excellent charge/discharge reversibility. LiMnPO4 has a redox potential of 4,1 V versus Li⁺/Li which is considered to be the maximum limit accessible to the most liquid electrolytes.

Also, lithium manganese oxide (LiMn₂O₄) spinel 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 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. Recently, a new class of 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 olivine and spinel structures by modified sol-gel method. Examples are: olivins – LiFePO₄, LiMnPO₄ [2] and spinels: LiMn₂O₄ (stoichiometric, nonstoichiometric and substituted) [3,4] and Li₄Ti₅O₁₂.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). All obtained materials were single phase and with nano size of crystallites. 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.

[1] A. K. Padhi, K. S. Nanjundaswamy, J. B. Goodenough: Phospho-olivines as Positive-Electrode Materials for Rechargeable Lithium Batteries, J. Electrochem. Soc. 144 (4) (1997) 1188-1194.

[2] K. P. Korona, J. Papierska, M. Kamińska, A. Witkowski, M. Michalska, L. Lipińska: Raman measurements of temperature dependencies of phonons in LiMnPO₄, Materials Chemistry and Physics 127 (2011) 391-396.

[3] 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.

[4] Monika Michalska, Ludwika Lipińska, Ryszard Diduszko, Marta Mazurkiewicz, Artur Małolepszy, Leszek Stobinski, 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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