Generation of cathode passivation films via oxidation of lithium bis(oxalato) borate on high voltage spinel (LiNi0.5Mn 1.5O4)

The reactions of lithium ion battery electrolyte (LiPF6 in ethylene carbonate/ethyl methyl, EC/EMC, 3:7 v/v) with and without added lithium bis(oxalato) borate (LiBOB) on the surface of high voltage LiNi 0.5Mn1.5O4 cathodes has been investigated via a combination of electrochemical measurements, in situ gas analysis, and ex situ surface analysis. The oxidation of LiBOB on the cathode results in the generation of CO2 and a cathode passivation film containing borate oxalates. The cathode passivation film inhibits oxidation of the bulk electrolyte at high potential (\u3e4.8 V vs Li/Li+). © 2014 American Chemical Society

Reactivity of Amide Based Solutions in Lithium–Oxygen Cells

The stability of electrolyte solutions during lithium–oxygen cells operation is of great importance and interest. This is because oxides formed during reduction are strong nucleophiles which can initiate solvent decomposition. The highly polar amide based solvents have come to the fore as possible candidates for Li–O₂ applications. They show typical cycling behavior as compared to other solvents; however, their stability toward lithium oxides is shrouded in doubt. The present study has focused on Li–O₂ cells containing electrolyte solutions based on DMA/LiNO₃. We have used various analytical tools, to explore the discharge–charge processes and related side reactions. The data obtained from FTIR, NMR, XPS, and EQCM all support a rational decomposition mechanism. The formation of various side products during the course the first discharge, leads to the conclusion that amide based solvents are not suitable for Li–O₂ applications; however, electrolyte solution decomposition reduces the OER overpotential by forming oxidation mediators

On the Challenge of Electrolyte Solutions for Li–Air Batteries: Monitoring Oxygen Reduction and Related Reactions in Polyether Solutions by Spectroscopy and EQCM

Polyether solvents are considered interesting and important candidates for Li–O₂ battery systems. Discharge of Li–O₂ battery systems forms Li oxides. Their mechanism of formation is complex. The stability of most relevant polar aprotic solvents toward these Li oxides is questionable. Specially high surface area carbon electrodes were developed for the present work. In this study, several spectroscopic tools and in situ measurements using electrochemical quartz crystal microbalance (EQCM) were employed to explore the discharge–charge processes and related side reactions in Li–O₂ battery systems containing electrolyte solutions based on triglyme/lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) electrolyte solutions. The systematic mechanism of lithium oxides formation was monitored. A combination of Fourier transform infrared (FTIR), NMR, and matrix-assisted laser desorption/ionization (MALDI) measurements in conjunction with electrochemical studies demonstrated the intrinsic instability and incompatibility of polyether solvents for Li–air batteries

Understanding the behavior of Li-oxygen cells containing LiI

Mankind has been in an unending search for efficient sources of energy. The coupling of lithium and oxygen in aprotic solvents would seem to be a most promising direction for electrochemistry. Indeed, if successful, this system could compete with technologies such as the internal combustion engine and provide an energy density that would accommodate the demands of electric vehicles. All this promise has not yet reached fruition because of a plethora of practical barriers and challenges. These include solvent and electrode stability, pronounced overvoltage for oxygen evolution reactions, limited cycle life and rate capability. One of the approaches suggested to facilitate the oxygen evolution reactions and improve rate capability is the use of redox mediators such as iodine for the fast oxidation of lithium peroxide. In this paper we have examined LiI as an electrolyte and additive in Li oxygen cells with ethereal electrolyte solutions. At high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product. In turn, the presence of oxygen facilitates the reduction of I-3(-) to 3I(-) in these systems. At very low concentrations of LiI, oxygen is reduced to Li2O2. The iodine formed in the anodic reaction serves as a redox mediator for Li2O2 oxidation

Fluoroethylene Carbonate as an Important Component in Electrolyte Solutions for High-Voltage Lithium Batteries: Role of Surface Chemistry on the Cathode

The effect of fluorinated ethylene carbonate (FEC) as a cosolvent in alkyl carbonates/LiPF₆ on the cycling performance of high-voltage (5 V) cathodes for Li-ion batteries was investigated using electrochemical tools, X-ray photoelectron spectroscopy (XPS), and high-resolution scanning electron microscopy (HRSEM). An excellent cycling stability of LiCoPO₄/Li, LiNi_0.5Mn_1.5O₄/Si, and LiCoPO₄/Si cells and a reasonable cycling of LiCoPO₄/Si cells was achieved by replacing the commonly used cosolvent ethylene carbonate (EC) by FEC in electrolyte solutions for high-voltage Li-ion batteries. The roles of FEC in the improvement of the cycling performance of high-voltage Li-ion cells and of surface chemistry on the cathode are discussed