Hydrogen evolution reactions that cause the alkalization of aqueous electrolytes generally frustrate the structural stability and cycling performance of NaTi 2 (PO 4 ) 3 /C anode material for rechargeable aqueous sodium-ion batteries (ASIBs). Herein, a novel highly concentrated electrolyte with a large hydrogen-evolution overpotential and hydroxide-capture ability is rationally established by incorporating a bifunctional Mg(Ac) 2 additive into a concentrated NaAc aqueous solution. The highly concentrated electrolyte salts (4 m NaAc+3 m Mg(Ac) 2 ) favor regulation on hydrogen-bonding configurations and kinetically shift the hydrogen evolution potential to a lower value of −1.37 V (vs Ag/AgCl). The Mg(Ac) 2 additive plays particular roles in spontaneously capturing hydroxide ions generated during hydrogen evolution reactions on anode surfaces and simultaneously forming a protective Mg(OH) 2 -like interphase. As a result, the unique electrolyte significantly improves the structural stability and cycling performance of NaTi 2 (PO 4 ) 3 /C anode (94.8% capacity retention after 100 cycles at 100 mA·g −1 ). The effect of salt concentration on hydrogen bonding configurations of aqueous electrolytes is investigated with Raman spectroscopy and FTIR spectroscopy. The interphase is identified by coupling EDS mapping, X-ray photoelectron spectroscopy, and X-ray diffraction. This work provides a new strategy for improving the cycling stability of aqueous sodium-ion batteries.
Jing Lin,Fei Liang,Yaoming Wu,Wanqiang Liu,Limin Wang
We prepared Ti 1.4 V 0.6 Ni ribbons by arc-melting and subsequent melt-spinning techniques. Ti 1.4 V 0.6 Ni + x Mg ( x = 1, 1.5, 2, 2.5 and 3, wt.%) composite alloys were obtained by the mechanical ball-milling method. The structures and hydrogen storage properties of alloys were investigated. Ti 1.4 V 0.6 Ni + x Mg composite alloys contained icosahedral quasicrystalline phase, Ti 2 Ni-type phase, β-Ti solid-solution phase and metallic Mg. The electrochemical and gaseous hydrogen storage properties of alloys were improved with Mg addition. Ti 1.4 V 0.6 Ni + 2 Mg alloy showed maximum electrochemical discharge capacity of 282.5 mAh g −1 as well as copacetic high-rate discharge ability of 82.3% at the discharge current density of 240 mA g −1 compared with that of 30 mA g −1 , and the cycling life achieved above 200 mAh g −1 after 50 consecutive cycles of charging and discharging. The hydrogen absorption/desorption properties of Ti 1.4 V 0.6 Ni + x Mg ( x = 1, 2 and 3, wt.%) alloys were better than Ti 1.4 V 0.6 Ni. Ti 1.4 V 0.6 Ni + 3 Mg alloy also exhibited a favorable hydrogen absorption capacity of 1.53 wt.%. The improvement in the hydrogen storage characteristics caused by adding Mg may be ascribed to better hydrogen diffusion and anti-corrosion ability.
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