Compatibility of Li[sub x]Ti[sub y]Mn[sub 1−y]O[sub 2] (y=0, 0.11) Electrode Materials with Pyrrolidinium-Based Ionic Liquid Electrolyte Systems

Abstract

The possibility of using electrolyte systems based on room-temperature ionic liquids ͑RTILs͒ in lithium-battery configurations is discussed. The nonflammability and wide potential windows of RTIL-based systems are attractive potential advantages, which may ultimately lead to the development of safer, higher energy density devices than those that are currently available. An evaluation of the compatibility of these electrolyte systems with candidate electrodes is critical for further progress. A comparison of the electrochemical behavior of Li/RTIL/Li x MnO 2 and Li x Ti 0.11 Mn 0.89 O 2 cells with those containing conventional carbonate solutions is presented and discussed in terms of the physical properties of two RTIL systems and their interactions with the cathodes. Strategies to improve performance and minimize cathode dissolution are presented.The worldwide market for rechargeable lithium batteries currently exceeds U.S. $3 billion per year. 1 These devices are primarily for consumer applications, such as cell phones and laptop computers, but lithium-ion battery sales are projected to capture 5% of the hybrid and electric vehicle market by 2010, and 36% by 2015. 2 Safety requirements for vehicular applications are particularly stringent, and, in many cases, higher energy densities are needed than those that are currently available. Further improvements over the state of the art are needed to achieve these goals.Of particular interest for these applications are room-temperature ionic liquids ͑RTILs͒ because of several unique properties, including low volatility, low flammability, thermal and chemical stability, high ionic conductivity, and wide potential windows. 3 RTILs are ionic salts that are liquid over a wide temperature range, characteristically from below room temperature to above 200°C. Typical ionic liquids consist of quaternary ammonium cations and anions with low Lewis basicity. For example, the combination of 1-ethyl-3-methylimidazolium cations with various anions produces RTILs with low-enough viscosity and high-enough conductivity to be applied to different energy storage devices. 4,5 However, the practical application of imidazolium-based ionic electrolytes for lithium batteries is not possible because imidazolium cations are reduced at the surface of lithium metal at around 1 V vs Li + /Li. 6 RTILs based on tetraalkylammonium, pyrrolidinium, or piperidinium cations are somewhat more stable against reduction on lithium metal and these have shown better prospects for use in lithium batteries. 7-9 For example, it has been found that systems based on N-methyl-N-alkyl pyrrolidinium cations ͑P 1X + , where the subscript indicates the lengths of the alkyl chains coordinated to the pyrrolidinium nitrogen͒, and bis͑trifluoromethanesulfonyl͒imide ͑TFSI͒ anions ͑Fig. 1͒ allow lithium to be cycled with a high degree of reversibility such that cycling efficiencies exceeding 99% have been obtained. 10 The reversible cycling is attributed to the presence of the P 1X + cation, which is stable at negative poten...

Ionic Liquids with the Bis(fluorosulfonyl)imide Anion: Electrochemical Properties and Applications in Battery Technology

“…[16][17][18] At a platinum electrode, mixtures of C 3 mpyrFSI and LiTFSI not only display reversible lithium electrochemistry, 14 but the behavior is also characterized by a shift of Ͼ1 V in the cathodic reduction limit for the electrolyte. 19 This is consistent with the behavior expected when both Li + and TFSI − ions are present ͑see above͒.…”

Lithium batteries: Status, prospects and future

“…In the meantime, given to the actual high cost, it is likely that ILs, rather than full electrolyte media, will be used as additives to the common organic liquid electrolyte solutions [51,52].…”

Electrode Materials with the Na0.44MnO2 Structure: Effect of Titanium Substitution on Physical and Electrochemical Properties

“…6,7 Partial substitution appears to impart resistance against dissolution and degradation of the material in electrochemical cells with LiPF 6 -containing electrolytic solutions at elevated temperature. 5 Saint et al 8 have also observed a similar protective effect in cells with pyrrolidinium-based ionic liquid electrolytes; Li x MnO 2 undergoes rapid capacity fading due to an electrochemically induced dissolution/precipitation reaction whereas and SS-or GNC-Li x Ti 0.11 Mn 0.89 O 2 to specify which of the sodium-containing precursors was used in their preparation.…”