Novel Lithium Manganese Silicate with Stable Structure upon Cycling As Positive Electrode for Lithium-Ion Batteries

Abstract

Lithium manganese silicate Li2MnSiO4 is theoretically one of the most interesting polyanionic material for lithium-ion batteries positive electrode. Its theoretical capacity reaches 333mAh/g thanks to the possible exchange of two lithium ions per formula unit which happens below the organic electrolyte degradation voltage. Indeed, the first lithium ion is calculated to be exchanged at 4.1V vs Li+/Li and the second one at 4.4V [1]. The high energy density combined with the thermal stability of the Si-O bond make Li2MnSiO4 in theory one of the best choice to equip the next generation of electrified transportation [2]. 1st studied in 2006 by Dominko et al. [3], lithium manganese silicate still shows severe limitations. Both its ionic and electronic conductivities are low [4] and Li2MnSiO4 structure cannot accommodate large Li+ extraction without amorphization. Thus, it leads to high polarization and capacity fading during cycling, impeding its practical interest. Despite this trend, manganese-based silicate polyanions are essentially interesting because of their high abundance, low cost and environmental friendliness. Here we propose an unreported manganese silicate material that we recently patented. This new material, usable as a positive electrode for lithium ion batteries, showed remarkable cycling stability. 100 mAh/g were obtained in half-cells versus lithium metal counter-electrode (Figure 1). Ex-situ X-Ray Diffraction showed that the structure was maintained during cycling, demonstrating that the material can accommodate reversible extraction of Li+ ions. To limit particle growth careful attention was paid on the synthesis route. Primary particles of 50 nanometers were obtained by a sol-gel process (Figure 2). Rate capabilities of the material, studied by galvanostatic cycling, will also be presented. Deeper characterization by X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy-Selected Area Electron Diffraction (TEM-SAED) and Differential Scanning Calorimetry (DSC) will be shown to assess the redox process, structure and thermal stability of this material. [1] Arroyo-de Dompablo et al., Electrochem. Commun., 2006, 8, 1292–1298 [2] Andre et al., J. Mater. Chem. A, 2015, 3, 6709–6732 [3] Dominko et al., Electrochem. Commun., 2006, 8, 217–222 [4] Dominko et al., J. Power Sources, 2008, 184, 462–468 Figure 1