  The concept of green in a battery involves the chemical nature of electrodes
and electrolytes as well as the economic sustainability of the cell. Although
these aspects are typically discussed separately, they are deeply
interconnected: indeed, a new electrolyte can allow the use of different
cathodes with higher energy, lower cost or more pronounced environmental
compatibility. We focus on alternative class of electrolyte solutions for
lithium batteries formed by dissolving LiX salts in glyme solvents, i.e.,
organic ethers with the molecular formula CH3O[CH2CH2O]nCH3 differing by chain
length. The advantages of these electrolytes are illustrated in terms of
flammability, stability, toxicity, environmental compatibility, cell
performances and economic impact. A particular light is shed on the stability
of these systems, particularly in the polymer state, and in various
environments including oxygen, sulfur and high-energy lithium metal. The most
relevant studies on the chemical-physical features, the characteristic
structures, the favorable properties, and the electrochemical behavior of the
glyme-based solutions are discussed, and the most recent technological
achievements in terms of cell design and battery performance are described. The
use of glyme-based electrolytes in high-energy cells arranged by coupling the
lithium-metal anode with conventional insertion cathodes as well as in
alternative and new batteries exploiting the Li-S and Li-O2 conversion
processes are described in detail. The paragraphs reveal bonuses, including
safety, low cost and sustainability, that can be achieved by employing the
glyme-based electrolytes with respect to the commercially available ones, in
particular taking into account future and alternative applications. Particular
relevance is given by the glymes with long chain that reveal a remarkable
stability, high safety and very low toxicity.
