Ang Xiao

Examining the Solid Electrolyte Interphase on Binder-Free Graphite Electrodes

The solid electrode interphase (SEI) on graphite electrodes is important to the performance, calendar life, and safety characteristics of lithium-ion cells. This article examines the SEI formed on binder-free graphite electrodes prepared by electrophoretic deposition. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis data were obtained on electrodes cycled in cells containing four electrolytes comprising ethylene carbonate: ethylmethyl carbonate (3:7 by weight) solvent and 1.2 M LiPF{sub 6}, 1 M LiF{sub 2}BC{sub 2}O{sub 4}, 1 M LiBF{sub 4}, or 0.7 M LiB(C{sub 2}O{sub 4}){sub 2} salt. Our observations suggest that, in addition to solvent reduction, the reduction of electrolyte salts plays an important role in SEI formation. Mechanisms to account for the formation of these SEI constituents are included in the article.

Thermal Reactions of LiPF6 with Added LiBOB Electrolyte Stabilization and Generation of

The effect of thermal storage on 1.0 M LiPF 6 in 1:1:1 ethylene carbonate/dimethyl carbonate/diethyl carbonate with 5 wt % added lithium bisoxalatoborate [LiB(C 2 O 4 ) 2 LiBOB] was investigated. Thermal storage of LiPF 6 initiates disproportionation reactions of LiBOB, which generate LiBF 4 , lithium difluorooxalatoborate [LiBF 2 (C 2 O 4 ), LiF 2 OB], and lithium tetrafluorooxolatophosphate [LiPF 4 (C 2 O 4 ), LiF 4 OP]. The synthesis and characterization of LiF 4 OP are presented along with a preliminary electrochemical investigation of LiF 4 OP-based electrolytes.

Surface Analysis of Electrodes from Cells Containing Electrolytes with Stabilizing Additives Exposed to High Temperature

We have conducted a detailed investigation of the effect of thermal stabilizing additives, including dimethyl acetamide (DMAc), N-methyl pyrrolidone, vinylene carbonate (VC), and vinylethylene carbonate (VEC), on the reactions of the electrolyte with the surface of the electrodes in lithium-ion cells. Cells were constructed with mesocarbon microbead anodes, LiNi 0.8 Co 0.2 O 2 cathodes, and 1.0 M LiPF 6 in 1:1:1 ethylene carbonate/diethyl carbonate/dimethyl carbonate electrolyte with and without electrolyte additives. The cells were stored sequentially at 55, 60, and 65°C for 10 days at each temperature. The cells were then dismantled, and the surfaces of the electrodes were analyzed via a combination of infrared spectroscopy with attenuated total reflection, X-ray photoelectron spectroscopy, and scanning electron microscope-energy dispersive spectroscopy. The surface of the electrodes extracted from cells containing the baseline electrolyte contained thick surface films composed of electrolyte decomposition products. The addition of 1% DMAc inhibits the reaction of the electrolyte with surface of the electrodes, especially on the anode. The addition of 1.5% VC results in the formation of poly(vinylene carbonate) on both electrodes and inhibits the reaction of electrolyte with the electrodes, especially the cathode. The addition of 1.5% VEC or 10% DMAc did not significantly impede the reaction of the electrolyte with the electrodes.

Investigation of Lithium Tetrafluorooxalatophosphate [ LiPF4 ( C2O4 ) ] as a Lithium-Ion Battery Electrolyte for Elevated Temperature Performance

The thermal stability of lithium tetrafluorooxalatophosphate [LiPF 4 (C 2 O 4 )] electrolyte was investigated. Although the thermal stabilities of the solid LiPF 4 (C 2 O 4 ) and LiPF 6 were comparable, the thermal stability of the liquid LiPF 4 (C 2 O 4 )/carbonate electrolyte was better than LiPF 6 /carbonate electrolytes. Lithium-ion cells containing LiPF 4 (C 2 O 4 ) electrolyte had better capacity retention than LiPF 6 electrolyte containing cells upon cycling after storage at 65°C for 2 weeks. Ex situ analysis of the electrodes before and after storage at 65°C and cycling suggested that differences in the structures of the anode and cathode surface films contributed to the superior performance of cells containing LiPF 4 (C 2 0 4 ) electrolyte.

Investigation of Lithium Tetrafluorooxalatophosphate as a Lithium-Ion Battery Electrolyte

A lithium tetrafluorooxalatophosphate [LiPF 4 (C 2 O 4 )] salt, was prepared and its properties as a lithium-ion battery electrolyte were investigated. The conductivity, electrochemical stability, and cycling performance of 1.0 M LiPF 4 (C 2 O 4 ) in 1:1:1 ethylene carbonate/dimethyl carbonate/diethyl carbonate are comparable to the industry standard LiPF 6 electrolyte. While the reversible capacity of the first cycle is lower than LiPF 6 -based electrolytes, the reversible cycling efficiency is equivalent. Electrochemical impedance spectroscopy and electrode surface analysis provide insight into the differences between LiPF 6 and LiPF 4 (C 2 O 4 ).

Novel Electrolyte for Lithium Ion Batteries: Lithum Tetrafluorooxalatophosphate (LiPF4C2O4)

A novel salt for lithium ion battery electrolytes, lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), has been prepared and investigated. The conductivity, electrochemical stability, and cycling performance of 1.0 M LiPF4(C2O4) in 1:1:1 ethylene carbonate:dimethyl carbonate:diethyl carbonate are comparable to the industry standard LiPF6 electrolyte. However, the LiPF4(C2O4) electrolyte has much better thermal stability. LiPF4(C2O4) electrolytes are a promising alternative for lithium ion batteries.