| Non-aqueous rechargeable Li-O2 batteries have attracted increasing attention due to their higher theoretical specific energy(11000 Wh kg-1)compared with conventional lithium-ion batteries?LIBs?.Li-O2 batteries are expected to be widely applied as new energy storage systems for electric vehicles and other electric devices.Despite much research efforts have been devoted on Li-O2 batteries,some significant barriers still limit the practical application of Li-O2 batteries including the poor cycling stability and the low rate capability.The viscosity and oxygen solubility and diffusion of electrolyte has a great effect on rate capability of Li-O2 battery.In our experiment,Triethylene glycol dimethyl ether?G3?was evaluated as an electrolyte solvent for non-aqueous lithium-oxygen?Li-O2?batteries.G3??=2.5 cP?has much lower viscosity than G4??=4.05 cP?,then G3(H02=5.6 molm-3bar-1,DO2=3.2 molm-3bar-1)has higher oxygen solubility and oxygen diffusion than G4(H02=4.3 molm-3bar-1,DO2=2.6 molm-3bar-1).At a higher current density of 2.5 A g-1,the discharge capacity of the battery using the G3-based electrolyte was about 1472 mAh g-1,which is about four times higher than that of the battery using the G4-based electrolyte.Then,at current density of 1 A g-1carbon with a fixed capacity of 1000 mAh g-1,the battery using the G3-based electrolyte can be operated stably for 80 cycles,while only 20cycles were achieved by using the G4-based electrolyte.Therefore,we think the G3-based electrolyte could be a proper alternative electrolyte to the conventional G4-based electrolyte.Besides,decomposition of separator or electrolyte is one of the main problems that lead to the bad cycling stability of Li-O2 battery.In our experiment,we found tannic acid?TA?has the ability of anti-radicals.Thus,we tested the radical scavenging capability of TA,and successfully coated the tannic acid on the surface of PP membrane due to its self-polymerization.The TA protected the PP separator from the attack of superoxide radicals,and scavenged the O2·-,which greatly improved the electrochemical performance,especially cycling stability of Li-O2 battery.With a fixed discharge voltage of 2 V,the cycle number of TA-PP based Li-O2 battery?100 cycles?is much greater than that of PP based battery?60 cycles?under current density of 500 mA g-1 with a fixed capacity of 1000 mAh g-1.Furthermore,polymer electrolytes Li-O2 battery is very attracting nowadays,which can make up many problems that liquid electrolytes possess.In our experiment,a polymer lithium-oxygen battery based on the lithiated perfluorinated sulfonic conducting ionomer swollen with non-aqueous solvent used as both electrolyte and separator is successfully operated at room temperature,and shows good cycling stability and rate capability,at a fixed capacity of 1000 mAh g-1 and 1.0 A g-1,the Li-O2batteries with the PFSA-Li polymer electrolyte shows good cycling stability,and can be operated stably for 55 cycles.The addition of 50 mM LiI to the PFSA-Li/DMSO polymer electrolyte led to a noticeable drop in the overpotential,the battery with the PFSA-Li/DMSO+LiI polymer electrolyte can be operated stably for 100 cycles.After cycling process,the stability of polymer membrane was evaluated by FT-IR and 19FNMR,the results demonstrate the good stability of PFSA-Li polymer electrolyte.Thus,PFSA-Li polymer electrolyte maybe the proper candidate for the typical liquid electrolytes for Li-O2 battery. |
PDF Full Text Request