To investigate physicochemical relationships between ionic radii, valence number and cationic metal species in electrolyte solutions, propylene carbonate with Li[N(SO 2 CF 3 ) 2 ], Na[N(SO 2 CF 3 ) 2 ], Mg[N(SO 2 CF 3 ) 2 ] 2 and Ca[N(SO 2 CF 3 ) 2 ] 2 were prepared. The temperature dependence of density, viscosity, ionic conductivity (AC impedance method) and self-diffusion coefficient (pulsed-gradient spin-echo nuclear magnetic resonance) was measured. The effects of cationic radii and cation valence number on the fluidity and transport properites (conductivity and self-diffusion coefficient) were analyzed. Research and development of lithium-ion batteries (LIBs) have focused on the efficient use of energy. Application fields of LIBs are spreading from portable commercial use (mobile phone and laptop PC) to large-scale energy systems (electric vehicle and accumulator for household use).1 Furthermore, the usages (utilities, needs, requirements and demands) of industrial-scaled electricity storage systems using LIBs are increasing for applications alongside renewable energy systems (photovoltaics and/or wind energy) and frequency regulation demands. However, resources and stock amounts of Li are limited. Another reactive cationic species, such as high Clarke number Na + (2.63, 6th) and divalent cations Mg 2+ (1.93, 8th) and Ca 2+ (3.39, 5th) have been reported as new cationic species for next-generation batteries (Li + : 0.0006, 27th). 2 The number of reports for battery operations using a Na (sodium) system is increasing, and they have focused on the research and development of electrode and electrolyte materials for, mainly, positive electrodes.3-5 Because of the differences of ionic radii between Li + (60 pm) and Na + (95 pm), understanding the effects of ionic radii on electrolyte properties is important. 6,7 In addition, comparison between monovalent cations and divalent cations (Mg 2+ : 65 pm, 8 Ca 2+ : 99 pm 9 ) is also important to understand the effects of valence number of cation on the electrolyte properties. In this study, an electrolyte solutions of propylene carbonate (PC) and N(SO 2 CF 3 ) 2 − ([TFSA] − ) anion-based metal (Li, Na, Mg and Ca) salts were prepared and evaluated by measuring their physicochemical properties. We investigate the dependence of static (density) and dynamic (macroscopic fluidity: viscosity, ionic mobility: ionic conductivity and microscopic ionic diffusivity: self-diffusion coefficient) properties of electrolytes on the cationic metal species of salts (ionic radii and valence number) and salt concentrations. We also analyze the intermolecular interactions of the cations with PC and [TFSA] − by ab initio molecular orbital calculations. Using the mearurements of static and dynamic properties and analysis of interactions, the expectations of innovative next-generation battery systems are discussed. ExperimentalMaterials.-PC (Kishida Chemical, battery grade) and metal cation salts (Table I) were used as the solvent and dissolved salts for electrolyte solutions, respectively...

The development of new electrolytes for lithium–sulfur (Li–S) batteries is important. Electrolytes based on 1:1 glyme:Li+ complexes can be locally destroyed to form free glyme during charge/discharge cycles. Free glyme can cause Li2Sx dissolution, which is a major factor in Li–S battery degradation. To decrease the local generation of free glyme, the glyme:Li+ electrolytes with higher proportions of Li salts are developed to control the Li2Sx dissolution into the electrolyte. The chemical solubility of Li2S8 and the charge/discharge properties of Li–S cells are investigated by varying the glyme:Li salt molar ratio. Nonequimolar (high Li salt concentration) glyme:Li salt mixture electrolytes directly suppress the Li2S8 dissolution and improve the charge/discharge properties (cycling and coulombic efficiency) of Li–S cells. The electrolyte composition can control the chemical stability of reactive intermediates at the Li2Sx electrode and provide high‐performance Li–S cells for next‐generation batteries.

Highly-concentrated and low viscosity electrolyte for Li–S batteries.

Polyether-based polymer electrolytes containing an M x [N(SO2CF3)2] salt (x = 1 for Li and Na, 0.5 for Mg and Ca) were investigated for their thermal stabilities and ionic conductivities, owing to their high electrochemical stability and interfacial compatibility at electrodes as the electrolyte layer of all-solid-state batteries. The properties of an electrolyte / Na metal electrode interface were also explored. The thermal stability and ionic conductivity exhibited a strong correlation with the Coulombic interaction energy originating from cationic-radii and charge density derived from the cation’s valance number. The ionic conductivity of random copolymers of poly(ethyleneoxide) and poly(propyleneoxide) (P(EO/PO)) electrolytes increased slightly with decreasing cationic radii and decreased appreciably with valence number. In the [metallic electrode ∣ polymer electrolyte ∣ metallic electrode] cells, the interfacial resistances and their apparent activation energies at the polymer electrolyte / metallic electrode interfaces tended to be higher for the Na systems than for the Li systems. The calculated Na+ transport number exhibited a local maximum value when [Na]/[O] ∼0.04. To further evaluate the diffusive properties of active ions, nuclear magnetic resonance one-dimensional imaging was performed. The self-diffusion coefficient of TFSA was confirmed to correspond to the valence number of cation in the P(EO/PO)-M x [N(SO2CF3)2] electrolytes.

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