Shuting Feng

Mapping a stable solvent structure landscape for aprotic Li–air battery organic electrolytes

Electrolyte instability is one of the greatest impediments that must be overcome for the practical development of rechargeable aprotic Li–air batteries. In this work, we establish a comprehensive framework for evaluation of the stability of potential organic electrolytes for aprotic Li–air batteries that is based on four key descriptors: Bond dissociation energy, deprotonation free energy (i.e., Acidity), Nucleophilic substitution free energy, and Electrochemical oxidation/reduction. These parameters were calculated for several classes of organic compounds. The chemical stability of the molecules was studied experimentally under conditions designed to mimic the aprotic Li–air battery environment (heating in the presence of excess KO2 and Li2O2). In general, the calculated and experimental data agreed well for alkanes, alkenes, ethers, aromatics, carbonates, and S-containing and N-containing compounds. Using this dataset, we identified functional groups and other structural features of organic molecules that may be suitable for aprotic Li–air battery electrolyte design.

Fluorinated Aryl Sulfonimide Tagged (FAST) salts: modular synthesis and structure–property relationships for battery applications

Solid-state electrolytes are attracting great interest for their applications in potentially safe and stable high-capacity energy storage technologies. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is widely used as a lithium ion source, especially in solid-state polymer electrolytes, due to its solubility and excellent chemical and electrochemical stability. Unfortunately, chemically inert LiTFSI cannot be easily modified to optimize its properties or allow for conjugation to other molecules, polymers, or substrates to prepare single-ion conducting polymer electrolytes. Chemical modifications of TFSI often erode its advantageous properties. Herein, we introduce Fluorinated Aryl Sulfonimide Tagged (FAST) salts, which are derived from successive nucleophilic aromatic substitution (SNAr) reactions. Experimental studies and density functional theory calculations were used to assess the electrochemical oxidative stabilities, chemical stabilities, and degrees of ion dissociation of FAST salts as a function of their structures. FAST salts offer a platform for accessing functional sulfonimides without sacrificing many of the advantageous properties of TFSI.

Hot lithium-oxygen batteries charge ahead

Molten salt electrolytes and nickel oxide–based electrodes enable four-electron transfer The need to increase the energy storage per unit mass or volume and to decrease stored-energy cost from solar and wind (1) has motivated research efforts toward developing alternative battery chemistries. In particular, lithium-oxygen (Li-O2) batteries offer great promise (2, 3). During discharge, oxygen can be reduced to form either peroxide (Li2O2 in a two-electron pathway) or oxide (Li2O in a four-electron pathway). The estimated energy densities of lithium-oxygen batteries based on peroxide and oxide are two and four times higher than that of lithium-ion batteries, respectively (3), but degradation of organic electrolytes and of oxygen electrodes (typically made of carbon) by these reactive oxygen species has limited the reversibility of these systems. On page 777 of this issue, Xia et al. (4) address these issues by using inorganic components—a molten salt electrolyte and a nickel-based oxide supported by stainless steel mesh for the oxygen electrode—and demonstrate reversible operation for the four-electron–pathway Li-O2 battery at 150°C.