Lithium-ion batteries are becoming increasingly important for electrifying the modern transportation system and, thus, hold the promise to enable sustainable mobility in the future. However, their large-scale application is hindered by severe safety concerns when the cells are exposed to mechanical, thermal, or electrical abuse conditions. These safety issues are intrinsically related to their superior energy density, combined with the (present) utilization of highly volatile and flammable organic-solvent-based electrolytes. Herein, state-of-the-art electrolyte systems and potential alternatives are briefly surveyed, with a particular focus on their (inherent) safety characteristics. The challenges, which so far prevent the widespread replacement of organic carbonate-based electrolytes with LiPF6 as the conducting salt, are also reviewed herein. Starting from rather "facile" electrolyte modifications by (partially) replacing the organic solvent or lithium salt and/or the addition of functional electrolyte additives, conceptually new electrolyte systems, including ionic liquids, solvent-free, and/or gelled polymer-based electrolytes, as well as solid-state electrolytes, are also considered. Indeed, the opportunities for designing new electrolytes appear to be almost infinite, which certainly complicates strict classification of such systems and a fundamental understanding of their properties. Nevertheless, these innumerable opportunities also provide a great chance of developing highly functionalized, new electrolyte systems, which may overcome the afore-mentioned safety concerns, while also offering enhanced mechanical, thermal, physicochemical, and electrochemical performance.

In this study, we report on the electroplating and stripping of lithium in two ionic liquid (IL) based electrolytes, namely N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyr14FSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), and mixtures thereof, both on nickel and lithium electrodes. An improved method to evaluate the Li cycling efficiency confirmed that homogeneous electroplating (and stripping) of Li is possible with TFSI-based ILs. Moreover, the presence of native surface features on lithium, directly observable via scanning electron microscope imaging, was used to demonstrate the enhanced electrolyte interphase (SEI)-forming ability, that is, fast cathodic reactivity of this class of electrolytes and the suppressed dendrite growth. Finally, the induced inhomogeneous deposition enabled us to witness the SEI cracking and revealed previously unreported bundled Li fibers below the pre-existing SEI and nonrod-shaped protuberances resulting from Li extrusion.

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In this Full Paper we show that the use of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as conducting salt in commercial lithium-ion batteries is made possible by introducing fluorinated linear carbonates as electrolyte (co)solvents. Electrolyte compositions based on LiTFSI and fluorinated carbonates were characterized regarding their ionic conductivity and electrochemical stability towards oxidation and with respect to their ability to form a protective film of aluminum fluoride on the aluminum surface. Moreover, the investigation of the electrochemical performance of standard lithium-ion anodes (graphite) and cathodes (Li[Ni1/3 Mn1/3 Co1/3 ]O2 , NMC) in half-cell configuration showed stable cycle life and good rate capability. Finally, an NMC/graphite full-cell confirmed the suitability of such electrolyte compositions for practical lithium-ion cells, thus enabling the complete replacement of LiPF6 and allowing the realization of substantially safer lithium-ion batteries.

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Herein, cobalt orthosilicate (Co2SiO4, CSO) is presented as a new electrode material for rechargeable lithium-ion batteries. Orthorhombic α-Co2SiO4 (space group: Pbnm) was synthesized by a conventional solid-state method and subsequently characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). To study the reversible lithium uptake and release, cyclic voltammetry (CV), in situ XRD, as well as ex situ X-ray photoelectron spectroscopy (XPS) and SEM analysis were performed. Based on these results a new reaction mechanism is proposed including the reversible formation of lithium silicate. In addition, the electrochemical performance of CSO-based electrodes was investigated by galvanostatic cycling, applying varying specific currents. Such electrodes revealed a good high rate capability and a highly reversible cycling behavior, providing a specific capacity exceeding 650 mAh g(-1) after 60 cycles.

A VOx coating of Li1.2Mn0.56Ni0.16Co0.08O2, made through a low‐temperature annealing process (350 °C), results in the formation of a protecting layer, which enables electrodes to be prepared with an aqueous binder, offering a significantly improved electrochemical performance. The comparison with uncoated electrodes demonstrates the significantly improved performance of VOx‐coated Li1.2Mn0.56Ni0.16Co0.08O2, which substantially outperforms the uncoated material by 30 mAh g−1 at moderate rates. The VOx coating is found to prevent the contact of Li1.2Mn0.56Ni0.16Co0.08O2 with water from the aqueous‐binder processing, preventing leaching of metal cations. Upon cell operation, the coating delays the transformation of the active layer material into the spinel phase, occurring at low voltages, thus delaying its typical capacity fade upon cycling. Finally, the coating contributes to the overall material capacity, while ensuring the lithium deintercalation and intercalation processes.

Herein, we present an extensive physicochemical characterization of a series of fluorinated and nonfluorinated carbamates and their application as electrolyte solvents comprising lithium trifluoromethanesulfonyl imide (LiTFSI) as conducting salt. In a second step, these electrolyte compositions were characterized with respect to their ionic conductivity, salt dissociation, and electrochemical stability toward oxidation. In a third step, selected fluorinated electrolytes were studied concerning their ability to enable the utilization of LiTFSI as a conducting salt in the presence of an aluminum current collector by forming a protective aluminum fluoride surface layer, thus preventing the continuous anodic aluminum dissolution, i.e., aluminum corrosion. Finally, their electrochemical performance in combination with a state-of-the-art lithium-ion cathode material, Li­(Ni1/3Mn1/3­Co1/3)­O2 (NMC), was investigated. It is shown that higher fluorinated carbamates reveal a very stable cycling performance of such cathodes due to their ability to form a sufficiently thick, i.e., protective, aluminum fluoride layer on the surface of the aluminum current collector. These findings confirm their suitability as electrolyte solvents in combination with LiTFSI as a conducting salt, enabling the successful replacement of toxic and unstable LiPF6 for the development of intrinsically safer lithium-ion batteries.