Inorganic Porous Solid Electrolyte-cathode Components And Their Applications In Lithium-air Batteries

In the past decade,there have been exciting developments in the field of lithium ion batteries,which have been applied in areas ranging from small portable electric devices to larger power systems such as hybrid electric vehicles.However,because of the limited energy density,the lithium ion battery can’t meet the demands of electric vehicles for long distance transportation.Despite lithium-air battery owning very high theoretical energy density,there are still many problems such as electrochemical performance and safety.Among them,some intrinsic problems are caused by the use of organic liquid electrolytes,which are flammable and volatile.Solid-state lithium-air batteries using solid electrolytes instead of organic liquid electrolytes,have a better safety performance.But at the same time,solid electrolytes bring many new problems including the low conductivity and poor stability of solid electrolytes,slow reaction kinetics at cathode and large interfacial impedance.So,we did some research on the problems of cathode and electrolytesSolid electrolytes are the most important component of solid-state lithium-air batteries.First,we synthesized LAGP pellets by adjusting the Li2CO3 content in the raw materials.The highest ionic conductivity of LAGP pellets was 1.43×10-4 S cm-1.Among the LAGP pellets,only the LAGP pellet without excess Lithium had the ionic conductivity less than 10-4 S cm-1.In addition to LAGP,we also synthesized LLZTO pellet according to the variation of sintering time,ball milling speed and lithium source.The highest ionic conductivity achieved 2.32-10-4 S cm-1.In these three conditions,the change of the lithium source from Li2CO3 to LiOH·H2O suppressed effectively the grow of La2Zr2O7.But the ionic conductivity of the LLZTO pellet made from LiOH·H2O was merely 1.05×10-4 S cm-1.To avoid the reaction between LLZTO and the air,we stored the LLZTO in the argon glove box,but the ionic conductivity still fell by about half.Considering the air stability,we would not use LLZTO in the following experiment.After the LAGP was obtained,we used starch as pore-forming agent to prepare the porous LAGP pellet,and the diameter of the pore was essentially more than 10 μm.Then,we prepared a LAGP framework integrating the porous cathode and electrolyte via a simple one-step sintering.The interface contact between the porous cathode and electrolyte was good,and the overall ionic conductivity of LAGP framework was 4.58×10-5 S cm-1.Afterwards,carbon coating was through the carbonization process of four kinds of carbon sources under 700 °C.The carbon sources of carbohydrates brought us a higher carbon load and better battery performance.The solid-state lithium-air battery based on sucrose carbon coating won the highest discharge capacity of 842 mAh g-1.Because of the poor performance of solid-state lithium-air batteries,we tried to assemble the quasi-solid lithium-air battery.The battery exploited a composite electrolyte composed of porous LAGP and ionic liquid electrolyte LiTFSI-PYR14TFSI.The ionic conductivity of the around 50 μm thick composite electrolyte was 6.33×10-4 S cm-1.The introduction of PYR14TFSI could facilitate the charging reaction and reduced the charging platform to 3.2 V.The quasi-solid lithium-air battery using this composite electrolyte cycled over 10 times at a current density of 100 mA g-1 and a constant capacity of 1000 mAh g-1.