| Summary: | 碩士 === 國立臺南大學 === 綠色能源科技學系碩士班 === 104 === In the interest of expanding the available options for safe and inexpensive electrolyte in lithium ion batteries, we examined a novel electrolyte consisting of 30% IL (triethylmethylammonium bis(trifluoromethylsulfonyl)imide, N1222-TFSI) mixed with 70% commercial carbonate electrolyte (EC/DMC = 1:1 by wt%, 0.78 mol kg-1 LiPF6) to form a hybrid electrolyte. The hybrid electrolyte failed to ignite after exposure to flame, a demonstration of high thermal stability. The aluminum corrosion is inhibited in N1222-TFSI mixed carbonate electrolyte, while the N-methyl-N-propyl-pyrrolidinium TFSI mixed carbonate electrolyte experienced serious pitting corrosion. The electrolyte has been observed with the LiFePO4 as positive electrode and the mesophase graphite as negative electrode in 18650 full cells. The electrochemical properties of hybrid electrolyte for the LiFePO4 electrode at 25oC and 60oC showed improved performance at high temperature in comparison to commercial electrolyte EC/DMC (1:1 by wt%) 0.78 mol kg-1 LiPF6. Vinylene carbonate (VC) as electrolyte additive in hybrid electrolyte at 2.0% addition was found to enhance the cycling performance at 25oC and 60oC, however a decrease in cell performance was observed at -10oC.
Disordered carbons have been shown to possess high Na storage capacity. However, the mechanism of Na+ ion filled into disordered carbon is still controversial. The behaviors of sodium inserted in the hard carbon or spherical carbon electrode were investigated using high resolution neutron diffraction, cyclic voltammetry (CV), cyclability, and Transmission electron microscopy (TEM). Cyclic voltammetry indicates sodium metal plating and stripping on spherical carbon.The high resolution neutron diffraction has showed that spherical carbon consists of few-layer-stacked graphite nanocrystallites (around 1.8-3.0 nm) with large interlayer distances around 0.357 nm. Transmission electron microscopy has demonstrated that the Na-ion can be inserted into enlarged interlayer lattice carbon in nanospherical carbon and also show the Na metal crystal integrated in the nanopores between the few-layer-stacked graphite nanocrystallites domains in nanosphere carbon. The high resolution neutron diffraction has showed that crystal planes (200) and (220) of sodium metal in the hard carbon and spherical carbon electrodes were observed at room temperature, which were increased with decreasing the voltage states of electrode.
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