Design And Performance Of Solid-sate Li-S Battery With Evaporated Lithium Anode

Nowadays,commercial Li-ion batteries have achieved great success as power supplies for portable electronic equipment.Due to limited energy density,however,the existing lithium-ion batteries are difficult to meet the demands for long-distance transportation of electric vehicles and hybrid electric vehicles.From this point,the Li-S battery system is considered as a very promising candidate for new generation storage devices due to its high specific energy(2600 Wh kg-1).Though many efforts have been made during the past decades,it is still difficult to develop conventional Li-S batteries because they have suffered from serious problems,including:(1)the intrinsic nature of sulfur:low electrical conductivity.(2)Large volume expansion when sulfur dissolves and finally forms into Li2S;(3)the shuttle of soluble lithium polysulfide intermediates.Of which,the shuttle mechanism of lithium polysulfides may be the most severe problem in Li-S batteries,which leads to rapid capacity fading and low Coulombic efficiency.In this paper,to enhance the conductivity of cathode materials,sulfur was composited with multi-walled carbon nanotubes(S-MWCNT),in which the loading of sulfur is as high as 80%.The entangled mesh structure of MWCNT is more capable of bearing the volume expansion of the cathode materials while providing sufficient ion transport channels.In a battery with S-MWCNT as a cathode and in use of ordinary organic electrolyte,however,serious shuttle effect and poor cycle life are still remained to be improved.The NASICON-type Li1.5Al0.5Ge1.5(PO4)3(LAGP)with satisfactory ion conductivity(?10-4 S cm-1)and stable ability was used as the solid electrolyte.Two steps were further taken to improve the contacts of interfaces.Firstly,lithium thin film was directly deposited on the LAGP pellet by vacuum evaporation method to improve the contact between Li-LAGP interface.Secondly,small amount of ionic liquid was dropped on the S-MWCNT cathode to improve the contact of cathode and LAGP.Results showed that impedance of a solid-state battery with evaporated lithium is 60%decreased than that of a solid-state battery with ordinary lithium foil.In summary,we designed a new structure of solid-state battery with S-MWCNT composite as cathode dropped with small amount of ionic liquid,LAGP pellet as solid electrolyte,evaporated lithium film as anode.First discharge capacity of the battery with this structure was 1510 mAh g-1,indicating 90%of the theoretical capacity was achieved.After 30 cycles the discharge capacity displayed 1400 mAh g-1,with 94%of the initial capacity retained.The Coulombic efficiency of each cycle almost reached 100%.Results showed that this structure of solid-state batteries displayed excellent electrochemical performance.