Study On Practical Lithium Sulfur Battery Based On Low Tortuosity And High-loading Sulfur Cathode

Sulfur has attracted widespread attention owing to the advantages of high theoretical specific capacity(1675 m Ah g^–1),natural abundance,low price,and environmental friendliness.However,sulfur electrodes generally face issues of slow reaction kinetics and limited cycling lifespan due to the insulating properties of sulfur and the transformation reaction mechanism during charge-discharge processes.Low ionic and electronic transport of high-loading sulfur electrodes(>5 mg cm^–2)lead to low utilization of active materials,which seriously affects the energy density and cycling lifespan of practical lithium-sulfur batteries.Furthermore,the high-loading sulfur electrodes suffer from severe shuttle effect and dramatic volume changes during cycling,resulting in low coulombic efficiency and rapid capacity decay of lithium-sulfur batteries.With the purpose of realizing high-energy-density and long-cycling life practical cells(sulfur loading>5 mg cm^–2,E/S<5,and N/P<5),the high-loading sulfur cathodes with a low tortuosity structure（LTS）have been designed to promote ionic/electronic transport kinetics,thus improves electrochemical performance of practical battery.Simultaneously,a low-density electrolyte is designed to study the effect of electrolyte on the energy density and cycling performance of practical battery.A high-loading sulfur-based full battery is constructed by employing lithiated thick sulfur cathode and pre-lithiated silicon anode,and modified electrolyte further improves the cycling performance of full cells.The main conclusions are summarized as follows:（1）A high-loading sulfur cathode with a low-tortuosity structure（LTS）is designed and the effect of LTS on the electrochemical performance of the high-loading sulfur cathode is investigated.As a result,LTS significantly improves the ion/electron transport kinetics of electrodes.In addition,the electrodes also exhibit outstanding mechanical properties and integrity due to the addition of interwoven CFs that can tolerate the volume change during cycling and the dimensional deformation under a high compaction density.Benefiting from LTS,the Li-S cell with high-loading cathode(20.2 mg cm^-2)delivers a high initial energy density(390 Wh kg^-1)and maintains a high-capacity retention ratio of 80.8%after 140cycles at a low E/S of 2 and limited lithium（N/P=2.7）.（2）To further improve the energy density and cycling lifespan of the above practical batteries,a fluorobenzene diluted high-concentration electrolyte（FB-DHCE-3）with the advantages of low density,high ionic conductivity and interfacial stability is successfully designed.As the result,the high-loading sulfur cathode(20 mg cm^-2)exhibits excellent cycle stability（80.3%capacity retention over 191 cycles）at a low E/S of 2 and limited lithium（N/P=2.5）,and realizes a high energy density of coin cell(up to 441 Wh kg^-1).（3）Although the electrolyte design significantly improves the performance of the practical battery,the cycling lifespan is still limited by lithium metal anode.To avoid the issues of limited cycling lifespan and potential safety concerns of Li-S batteries arising from serious dendrite formation of Li metal anodes,the full battery is constructed by employing high-loading sulfur cathode and silicon anode.A modified FB-DHCE-3 electrolyte（FB-DHCE-F₃B）is designed to regulate film-forming properties of electrodes,aiming at improving electrochemical performance of high-loading sulfur-based full battery.As a result,FB-DHCE-F₃B shows high ionic conductivity,improving reaction kinetics of full battery.Simultaneously,FB-DHCE-F₃B exhibits excellent compatibility with prelithiated Se_0.05S_0.95@p PAN cathodes and prelithiated Si O_x anodes,which not only effectively accommodates the volume expansion of the lithiated Si O_x electrode,but also improves active material utilization of S cathode.