A long cycle-life Na-Mg hybrid battery with a chlorine-free electrolyte based on Mg(TFSI)2

The commercial applications of rechargeable magnesium batteries (RMBs) are hindered by the slow diffusion kinetic of Mg 2+ ions in cathode materials. To overcome this problem, we design a new Na-Mg hybrid battery with the NaTi 2 (PO 4 ) 3 @Carbon (NTP@C) nanoparticles as a cathode material, the Mg metal as an anode and the Mg(TFSI) 2  + NaBH 4 - triglyme/1,2-Dimethoxyethane (DME) as a hybrid electrolyte. For the first time, the Mg(TFSI) 2 is applied as a Mg 2+ ions source in the chlorine-free Na-Mg hybrid electrolyte with NaBH 4 as both Na + ions source and moisture scavenger. The NTP@C/Mg hybrid battery shows excellent electrochemical performance. The corresponding average capacity decay after 1000 cycles is only 0.004% and 0.008% per cycle at 2 C and 10 C, respectively. Even at 20 C, about 60 mAh g −1 can be obtained after 26000 cycles. The impressive capacity retention of 93.7% and 90.2% can be obtained at 5 and 10 C, respectively. The excellent electrochemical performance of the hybrid battery confirms the feasibility using Mg(TFSI) 2 in the chlorine-free hybrid electrolyte for long term cycle. The developed NTP@C/Mg hybrid battery possesses the advantages of excellent electrochemical performances, good safety and low cost, making it promising for the commercial applications, especially for the large-scale energy storages.