3 years ago

“Water-in-Salt” Electrolyte Makes Aqueous Sodium-Ion Battery Safe, Green, and Long-Lasting

“Water-in-Salt” Electrolyte Makes Aqueous Sodium-Ion Battery Safe, Green, and Long-Lasting
Chunsheng Wang, Xiiulin Fan, Fei Wang, Kang Xu, Oleg Borodin, Arthur V. Cresce, Wei Sun, Yong-Sheng Hu, Marshall A. Schroeder, Chongyin Yang, Xiaohui Rong, Shuyin Xu, Yuesheng Wang, Liumin Suo
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 Na0.66[Mn0.66Ti0.34]O2 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. The sodium-ion water-in-salt electrolyte with a wide electrochemical window is proposed through suppressing hydrogen evolution on anode with the formation of a Na+-conducting solid-electrolyte interphase and reducing the overall electrochemical activity of water on cathode. A full aqueous Na-ion battery constructed on Na0.66[Mn0.66Ti0.34]O2 as cathode and NaTi2(PO4)3 as anode exhibits superior performance at both low (0.2 C) and high (1 C) rates.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/aenm.201701189

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