No abstract

Passivation of the sulfur electrode by insulating lithium sulfide (Li2S) restricts the reversibility and sulfur utilization of lithium–sulfur (Li–S) batteries. Although electrolytes with high donor number (DN) solvents induce tri‐sulfur radical intermediate thus 3D nucleation of Li2S with fast kinetics can be achieved, their catastrophic reactivities with Li metal hinder practical applications. Here, the use of high DN solvent as an additive instead of as co‐solvent to solve their incompatibility between cathode and anode is proposed, by adopting N‐methyl‐2‐pyrrolidone (NMP) as a proof‐of‐concept. Such a strategy is accomplished by the unique solvation structure of the NMP added electrolyte, where the preference of NMP‐Li+ coordination squeezes out partial 1,2‐dimethoxyethane (DME) molecules while enriching 1,3‐dioxolane (DOL) molecules in the first solvation sheath of Li+ ions. It affords the robust SEI on Li metal from corrosion either by NMP or the dissolved polysulfides. Spectral analyses (Raman and UV–vis) also verify that the coordinated NMP additive preserves its S3•− radicals stabilization ability as it does as a co‐solvent, which effectively improves the sulfur conversion kinetics and reversibility. This approach enables competitive capacity retention and a stable cycling performance of 340 cycles, which is one of the longest lifespans known for the high DN solvent involved Li–S batteries.

The zinc-copper redox couple exhibits several merits, which motivated us to reconstruct the rechargeable Daniell cell by combining chloride shuttle chemistry in a zinc chloride-based aqueous/organic biphasic electrolyte. An ion-selective interface was established to restrict the copper ions in the aqueous phase while ensuring chloride transfer. We demonstrated that the copper-water-chloro solvation complexes are the descriptors, which are predominant in aqueous solutions with optimized concentrations of zinc chloride; thus, copper crossover is prevented. Without this prevention, the copper ions are mostly in the hydration state and exhibit high spontaneity to be solvated in the organic phase. The zinc-copper cell delivers a highly reversible capacity of 395 mAh g−1 with nearly 100% coulombic efficiency, affording a high energy density of 380 Wh kg−1 based on the copper chloride mass. The proposed battery chemistry is expandable to other metal chlorides, which widens the cathode materials available for aqueous chloride ion batteries.

Carbonyl oxygen atoms are the primary active sites to solvate Li salts that provide a migration site for Li ions conducting in a polycarbonate-based polymer electrolyte. We here exploit the conductivity of the polycarbonate electrolyte by tuning the segmental motion of the structural unit with carbonyl oxygen atoms, while its correlation to the mechanical and electrochemical stability of the electrolyte is also discussed. Two linear alkenyl carbonate monomers are designed by molecular engineering to combine methyl acrylate (MA) and the commonly used ethylene carbonate (EC), w/o dimethyl carbonate (DMC) in the structure. The integration of the DMC structural unit in the side chain of the in situ constructed polymer (p-MDE) releases the free motion of the terminal EC units, which leads to a lower glass-transition temperature and higher ionic conductivity. While pure polycarbonates are normally fragile with high Young's modulus, such a prolonged side chain also manipulates the flexibility of the polymer to provide a mechanical stable interface for Li-metal anode. Stable long-term cycling performance is achieved at room temperature for both LiFePO 4 and LiCoO 2 electrodes based on the p-MDE electrolyte incorporated with a solid plasticizer.

No abstract