Recently, lithium-ion batteries have been attracting more interest for use in automotive applications. Lithium resources are confi rmed to be unevenly distributed in South America, and the cost of the lithium raw materials has roughly doubled from the fi rst practical application in 1991 to the present and is increasing due to global demand for lithium-ion accumulators. Since the electrochemical equivalent and standard potential of sodium are the most advantageous after lithium, sodium based energy storage is of great interest to realize lithium-free high energy and high voltage batteries. However, to the best of our knowledge, there have been no successful reports on electrochemical sodium insertion materials for battery applications; the major challenge is the negative electrode and its passivation. In this study, we achieve high capacity and excellent reversibility sodium-insertion performance of hard-carbon and layered NaNi 0.5 Mn 0.5 O 2 electrodes in propylene carbonate electrolyte solutions. The structural change and passivation for hard-carbon are investigated to study the reversible sodium insertion. The 3-volt secondary Na-ion battery possessing environmental and cost friendliness, Na + -shuttlecock hard-carbon/NaNi 0.5 Mn 0.5 O 2 cell, demonstrates steady cycling performance as next generation secondary batteries and an alternative to Li-ion batteries.

Fluoroethylene carbonate is an efficient electrolyte additive to improve the reversibility of electrochemical sodium insertion for hard-carbon and NaNi(1/2)Mn(1/2)O(2) electrodes in aprotic Na cells. The additive is also capable of the electrochemical deposition/dissolution of metallic Na with higher reversibility because of improved passivation and suppression of side reactions between Na metal and propylene carbonate solution containing Na salts.

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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.