| The researches of efficient and pollution-free energy are getting great attention because the status quo of the energy crisis and the environment pollution is gradually deteriorating in recent years.The development of electric vehicles(EVs)is considered a feasible measure to relieve that problem.However,current conventional power systems such as lead-acid batteries,nickel-cadmium batteries,nickel-MH batteries,lithium-ion battery and so on can’t support the long-distance driving of electric vehicles.The lithium-air batteries with high theoretical specific energy(11140Wh/kg)are attracting more interest.They are considered the next generation power system for EVs.Nevertheless their commercial application is restricted by many problems,for instance the transfer tunnel for the oxygen is blocked by the discharge products which are not dissolved in the nonaqueous electrolyte and then the discharge is over ahead of time;the charge process of the lithium-air batteries is the decomposition of the lithium oxide with strong ionic bond,and it requires a high activation energy,the polarization of charge-discharge process makes the cycle efficiency of the batteries very low;the solubility and diffusion coefficient of oxygen in the nonaqueous electrolyte are very low,the discharge performance of the batteries with high-rate is not ideal,and the electrolyte systems such as the carbonate-based and ether-based and so on used in the lithium-air batteries are instability during the charge-discharge process of batteries,moreover the volatilization of the organic electrolyte is serious,all of them can lead the bad performance of the long-term work and cycle.Some basic researches as following are carried out in our paper for solving the above-mentioned problems:In the first part of our paper we prepared the air electrodes with double-layer structure(the gas diffusion layer and catalyst layer)which is usually used in proton exchange membrane fuel cell(PEMFC)to increase the discharge capacity,and some good results were obtained.We found that the gas diffusion layer(the carbon paper treated with PTFE)can support good tunnel for the transfer of the positive reactant oxygen and be good for the uniform distribution of the discharge products in air electrode.The catalyst layer fabricated by spraying attached to the fibers of the carbon paper,and that will enlarge the three-phase interface for the charge-discharge process.The air electrodes prepared with double-layer structure obtained higher discharge capacity than the air electrodes fabricated by spraying catalyst layer on the Celgard2400 membrane and coating the catalyst layer on the surface of the nickel foam.The air electrode with double-layer structure got a high discharge capacity of 6587mAh/g of carbon in pure oxygen at the rate of 0.15mA/cm2 when the carbon loading is 2.077mg/cm2.The effect of the catalysts(EMD,NiO,Co304,Fe203,a-Mn02,Pt and carbon powder without catalyst)on the performance of the air electrode was investigated in the second part of our paper.The catalytic activity of the catalysts on the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER)in the carbonate-based electrolyte was studied with two-electrode system,and the homemade a-Mn02 catalyst and the Pt/C catalyst purchased showed excellent catalytic activity for the ORR and OER.The homemade a-Mn02 catalyst got the highest discharge capacity and the best cycle performance in the subsequent charge-discharge process.We suggest that the effect of the catalysts on the first discharge capacity of the batteries is not outstanding,but the catalyst plays a important role in the subsequent charge-discharge process.In the third part,we synthesized a novel ionics liquid electrolyte(0.8M LiTFSI in[Bmim]TFSI)for the lithium-air batteries.And then we investigated the electrochemical characteristic and charge-discharge performance of three types of electrolytes as following:#1)1M LiPF6 in EC/EMC/DMC(weight ratio 1:1:1);#2)1M LiPF6 in EC/EMC/DEC(weight ratio 1:1:1);#3)0.8 M LiTFSI in[Bmim]TFSI.We found that the ORR in all three kinds of electrolyte was controlled by the diffusion of the oxygen.The high rate discharge performance of the batteries with the ionic liquid electrolyte was bad because of its high viscosity.The viscosity of the electrolyte#1)is lowest,and the batteries with the electrolyte#1)got the highest discharge capacity,the highest discharge voltage and the lowest charge voltage at the rate of 0.1mA/cm2.The volatilization of the ionic liquid electrolyte was weakest during the working of the batteries,the charge-discharge process of lithium-air batteries with the ionics liquid electrolyte have lasted for more than 2000 hours at the rate of 0.02mA/cm2. |
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