Dual electrolyte design for lithium-ion batteries
Examensarbete för masterexamen
Physics (MPPHS), MSc
The lithium-ion battery is the fastest growing energy storage technology, and dominates in demand for smaller portable applications and electric vehicles due to its high energy density, small weight, and long lifespan. New developments in the materials used as positive electrodes enable the battery cells to operate under higher voltages than their predecessors, increasing the maximal energy contained. However, the voltage range of these cells extends beyond the reduction and oxidation limits of conventional electrolyte solvents, causing degradation and subsequent failure. In this work, a dual electrolyte concept is proposed and evaluated, in which each electrode has its own catered electrolyte, reducing the voltage window each electrolyte must be electrochemically stable in. Pairs of immiscible electrolytes consisting of both organic solvents and room temperature ionic liquids were evaluated and the diffusion between them in a cell setting was studied by Raman confocal spectroscopy, showing little diffusion of higher viscosity ionic liquids. Furthermore, the electrochemical properties of the electrolyte pairs were tested by galvanostatic cycling, using lithium manganese nickel oxide (LNMO) and graphite as the cathode and anode respectively. An interface between two immiscible electrolytes, constituted by an ionic liquid and an organosulfur compound on one side, and an ether and a fluorinated carbonate ester on the other, was shown to allow for adequate mobility of ions in order to cycle a cell.
lithium-ion batteries, high voltage electrodes, LNMO, dual electrolytes, ionic liquids