Surface Film Formation on LiNi0.5Mn1.5O4 Electrode in an Ionic Liquid Solvent at Elevated Temperature

Abstract

A comparative study is made on the surface film formation on the high-voltage LiNi 0.5 Mn 1.5 O 4 positive electrode at elevated temperature (55 C) in two different electrolytes; LiPF 6 /organic carbonate and LiTFSI/ionic liquid (propylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide, PMPyr-TFSI). The surface film derived by a decomposition of the former electrolyte is enriched by inorganic fluorinated species, which becomes thicker with cycling to lead a continued electrode polarization and cell failure. In contrast, organic carbon species are dominant in the film derived from the latter electrolyte. This organic-rich film deposited in the earlier period of cycling seems to effectively passivate the positive electrode presumably due to uniform coverage. As a result, the film does not grow with cycling and electrode polarization is not serious to give a stable cycling behavior.

Electrolyte Formulations Based on Dinitrile Solvents for High Voltage Li-Ion Batteries

“…It was shown by Mun et al that Li/LMNO half cell with 1 M LiTFSI EC:DEC binary electrolyte solution fails during the first cycle due to Al corrosion 9 and so it was not surprising to observe rapid ecsdl.org/site/terms_use address. Redistribution subject to ECS license or copyright; see 132.246.78.…”

“…• C. 9 However, they show low high-rate battery performance, have high viscosity and are still expensive to make in large quantities.…”

Effect of Fluoroethylene Carbonate in the Electrolyte for LiNi0.5Mn1.5O4 Cathode in Lithium-ion Batteries

“…From Fig. 1a, it was observed that every cell has one short and two long voltage plateaus at 4.05, 4.76, and 4.72 V, which correspond to the electrochemical reactions of Mn 3+ /Mn 4+ , Ni 3+ /Ni 4+ , and Ni 2+ /Ni 3+ respectively [15,16]. Theoretically, the components of the LNMO cathode have the initial oxidation states of Ni 2+ and Mn 4+ .…”

“…Therefore, the researchers have been forced to search for other candidates operating at a high potential of over 4.2 V, so that there is a large potential gap between the anode and cathode. Among the various positive electrodes working at such a high potential, the spinel-type LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode has attracted much attention because of the high lithiation and delithiation potential of Ni 2+ /Ni 4+ (~4.7 V vs. Li/ Li + ), low cost of Mn and Ni ions, and the robust crystalline structure resulting from the stabilization of Mn 4+ by Ni 2+ doping [14][15][16]. However, the high operating potential is beyond the electrochemical stability window of conventional electrolytes, and this restricts the applicability of the LNMO cathode [14,16,17].…”

“…To demonstrate the physical and electrochemical characteristics of the FEC-oriented SEI on the high-voltage LNMO cathode, systematic analytical methods involving electrochemical, spectroscopic, and microscopic techniques were applied. The LNMO powders were prepared by the previously reported citric acid sol-gel method [16]. For electrochemical analyses, the composite electrodes were prepared by casting the slurry of the LNMO powder (active material), super-P (conducting agent, TIM-CAL), and polyvinyledene fluoride (binder, Solvay) in 94:3:3 and 80:10:10 wt% composition in N-methylpyrrolidinone (NMP; Sigma-Aldrich) solvent onto a piece of Al foil.…”