Preparation And Investigation Of Li₆PS₅Br Sulfide Electrolyte For All-solid-state Lithium Batteries

All-solid-state lithium battery（ASLB）based on inorganic solid electrolytes has the advantages of stable safety,high energy density,wide operating temperature range and long cycle life,making it a very promising next-generation energy storage device.Sulfide solid electrolytes（sulfide-SEs）have been paid close attention by the industry and the academia for their high ionic conductivity at room temperature and good mechanical performance.In our research,we explored the optimized sintering condition for the electrolyte synthesis,and boosted the electrochemical performances of the ASLBs by modifying the electrode-electrolyte interface and structing the ion-electron conduction network.The main works were summarized as follows:（1）Li₆PS₅Br solid electrolyte（LPSBr）was prepared via solid-state sintering method with Li₂S,P₂S₅ and Li Br as starting materials.The phases and ionic conductivity of the samples synthesized at various temperatures and heating rates were compared.It was found that Li₆PS₅Br electrolyte sintering at 550℃with 0.5℃min^-1 showed the highest purity and the highest ionic conductivity,reaching 1.22 m S cm^-1 at room temperature.Moveover,the test results evidenced that the SE has a wide electrochemical window,a high lithium ion transference number and a good ductility,which make it capable of being applied to ASLBs.（2）Fe₇S₈was chosen as an active material,and was compound with LPSBr via simple ball-milling.The effect of different carbon types on the electrochemical performance of the solid-state composite cathode was investigated.The results showed that Fe₇S₈–Li₆PS₅Br electrode with VGCF as the carbon additive had the best electrochemical performances compared with those containing Super-P or no carbon additives.VGCF improves the electronic conductivity and contact areas within the composite cathode.Therefore,the initial discharge capacity of the cathode reached 754.1 m Ah g^-1at 0.045 m A cm^-2 current density.While at a high current density of 0.45 m A cm^-2,the cathode still contributed a reversible capacity of 64.2m Ah g^-1.（3）A novel infiltration method was designed to prepare Fe₇S₈–LPSBr composite electrode in order to further improve the electrochemical performance of ASLBs.Li₆PS₅Br electrolyte was firstly dissolved into ethanol.It was found that adding Triton X100 dispersant can improve the purity and ionic conductivity of the electrolyte after the removal of ethanol.The ionic conductivity of the solvent-treated electrolyte was 0.67 m S cm^-1 at room temperature,which can meet the requirements of solid-state batteries.The SEs fill the pores of electrode well and form a smooth ionic conduction network within the composite electrode.Therefore,the infiltrated Fe₇S₈–LPSBr composite electrode displayed a reversible capacity of 527 m Ah g^-1 at0.045 m A cm^-2,remaining at 560 m Ah g^-1 after 100 cycles.At higher current density of 0.45m A cm^-2,its reversible capacity could reach 189 m Ah g^-1,which was almost triple that of the ball-milled composite cathode.