Journal
ADVANCED ENERGY MATERIALS
Volume 7, Issue 21, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201701189
Keywords
aqueous sodium-ion electrolyte; aqueous sodium-ion batteries; high concentrated electrolyte; sodium-ion batteries; water-in-salt
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Funding
- DOE ARPA-E [DEAR0000389]
- National Key R&D Program of China [2016YFB0901500]
- NSFC [51421002]
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Narrow electrochemical stability window (1.23 V) of aqueous electrolytes is always considered the key obstacle preventing aqueous sodium-ion chemistry of practical energy density and cycle life. The sodium-ion water-in-salt electrolyte (NaWiSE) eliminates this barrier by offering a 2.5 V window through suppressing hydrogen evolution on anode with the formation of a Na+-conducting solid-electrolyte interphase (SEI) and reducing the overall electrochemical activity of water on cathode. A full aqueous Na-ion battery constructed on Na-0.66[Mn0.66Ti0.34]O-2 as cathode and NaTi2(PO4)(3) as anode exhibits superior performance at both low and high rates, as exemplified by extraordinarily high Coulombic efficiency (>99.2%) at a low rate (0.2 C) for >350 cycles, and excellent cycling stability with negligible capacity losses (0.006% per cycle) at a high rate (1 C) for >1200 cycles. Molecular modeling reveals some key differences between Li-ion and Na-ion WiSE, and identifies a more pronounced ion aggregation with frequent contacts between the sodium cation and fluorine of anion in the latter as one main factor responsible for the formation of a dense SEI at lower salt concentration than its Li cousin.
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