Searching for the Best Electrolyte Composition for the C/Li2MnSiO4 Based Battery Systems

Li₂MnSiO₄ is one of the most promising among all of polianionic cathode materials for Li-ion batteries [1-5]. Thanks to its unique composition the material is characterized by high theoretical capacity (333 mAh g^-1) and potentially low production costs. On the other hand, the main disadvantage of Li₂MnSiO₄ is its extremely low electrical conductivity [2]. Preparation of nano-sized material and its modification by carbon coating is in this case essential to provide good electrochemical properties [1,2]. Another drawback of this material is its structural instability in charge/discharge process. There is a number of reports showing that Li₂MnSiO₄ cathode material undergoes amorphization in the first few charging/discharging cycles [3-5]. Degradation of crystalline structure can be explained by Jahn-Taller distortion associated with changes in lattice parameters during Mn³⁺ → Mn⁴⁺ transition.  Another explanation may be occurrence of secondary reactions between electrolyte and delithated forms of lithium manganese silicate (LiMnSiO₄ and MnSiO₄). The aforementioned structural changes of the material entail variations in electrochemical properties of Li₂MnSiO₄.

           The goal of these studies is to examine influence of different electrolyte composition on C/Li₂MnSiO₄stability and its electrochemical properties in the first charging/discharging cycles.

           For the purpose of this studies we chose a set of electrolytes characterized by different chemical behavior toward electrode materials. The various electrolytes compositions based on LiPF₆, LiClO₄, LiBOB and LTFSi salts in different solvents mixtures (EC/DMC, EC/DEC, TMS/EMC) were tested with C/Li₂MnSiO₄ nanocomposite. Li₂MnSiO₄was obtained via sol-gel synthesis. Active material was carbon coated using poly-N-vinylformamide with pyromellitic acid additive as carbon precursor. Electrochemical properties of assembled cells (CR2032 housing) were studied by galvanostatic charge/discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) methods.

            This work was supported by the International PhD-studies programme at the Faculty of Chemistry Jagiellonian University within the Foundation for Polish Science MPD Programme co-financed by the EU European Regional Development Fund. The authors acknowledge a financial support from the European Institute of Innovation and Technology under the KIC InnoEnergy NewMat project.

References:

[1] M.E. Arroyo-de Dompablo, M. Armand, J.M. Tarascon, U. Amator, Electrochem Commun 81292-1298 (2006).

[2] A. Kokalj, R. Dominko, G. Mali, A. Meden, M. Gaberscek, J. Jamnik, Chem Mater 193633-3640 (2007).

[3] M. Molenda, M. Świętosławski, A. Rafalska-Łasocha, R. Dziembaj Functional Material Letters 4135-138 (2011).

[4] V. Aravindan, S. Ravi, W.S. Kim, S.Y. Lee, J Colloid Interf Sci 355472–477 (2011).

[5] M. Świętosławski, M. Molenda, K. Furczoń, R. Dziembaj, J Power Sources 244 510-514 (2013).