Cobalt orthosilicate as a new electrode material for secondary lithium-ion batteries.

Herein, cobalt orthosilicate (Co2SiO4, CSO) is presented as a new electrode material for rechargeable lithium-ion batteries. Orthorhombic α-Co2SiO4 (space group: Pbnm) was synthesized by a conventional solid-state method and subsequently characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). To study the reversible lithium uptake and release, cyclic voltammetry (CV), in situ XRD, as well as ex situ X-ray photoelectron spectroscopy (XPS) and SEM analysis were performed. Based on these results a new reaction mechanism is proposed including the reversible formation of lithium silicate. In addition, the electrochemical performance of CSO-based electrodes was investigated by galvanostatic cycling, applying varying specific currents. Such electrodes revealed a good high rate capability and a highly reversible cycling behavior, providing a specific capacity exceeding 650 mAh g(-1) after 60 cycles.

Deep eutectic solvents based on N-methylacetamide and a lithium salt as suitable electrolytes for lithium-ion batteries.

In this work, we present a study on the physical and electrochemical properties of three new Deep Eutectic Solvents (DESs) based on N-methylacetamide (MAc) and a lithium salt (LiX, with X = bis[(trifluoromethyl)sulfonyl]imide, TFSI; hexafluorophosphate, PF6; or nitrate, NO3). Based on DSC measurements, it appears that these systems are liquid at room temperature for a lithium salt mole fraction ranging from 0.10 to 0.35. The temperature dependences of the ionic conductivity and the viscosity of these DESs are correctly described by using the Vogel-Tammann-Fulcher (VTF) type fitting equation, due to the strong interactions between Li(+), X(-) and MAc in solution. Furthermore, these electrolytes possess quite large electrochemical stability windows up to 4.7-5 V on Pt, and demonstrate also a passivating behavior toward the aluminum collector at room temperature. Based on these interesting electrochemical properties, these selected DESs can be classified as potential and promising electrolytes for lithium-ion batteries (LIBs). For this purpose, a test cell was then constructed and tested at 25 °C, 60 °C and 80 °C by using each selected DES as an electrolyte and LiFePO4 (LFP) material as a cathode. The results show a good compatibility between each DES and LFP electrode material. A capacity of up to 160 mA h g(-1) with a good efficiency (99%) is observed in the DES based on the LiNO3 salt at 60 °C despite the presence of residual water in the electrolyte. Finally preliminary tests using a LFP/DES/LTO (lithium titanate) full cell at room temperature clearly show that LiTFSI-based DES can be successfully introduced into LIBs. Considering the beneficial properties, especially, the cost of these electrolytes, such introduction could represent an important contribution for the realization of safer and environmentally friendly LIBs.