Research On Sepiolite Modification Of Lithium-Sulfur Battery Separator At The Cathode Side

With the development of electronic information and automobile industry,portable electronic equipment and electric vehicles are gradually popularized,where people raise higher demands for high-capacity rechargeable batteries.Sulfur,the cathode material for lithium-sulfur batteries,has raised interests from many researchers owing to its high theoretical capacity(1675 m Ah g^-1),abundant reserves and environmental benign.However,polysulfides are generated in the charging and discharging processes of lithium sulfur batteries,dissolve into the electrolyte and shuttle across the separator to the negative electrode,leading to irreversible capacity fade of lithium sulfur batteries.Accompanied with another issue of severe lithium dendrite growth on the lithium metal anode,the two challenges greatly hinder the commercialization of lithium-sulfur batteries.Separator modification and interlayers are effective solutions to the shuttle effect and dendrite growth.Here,we design a natural sepiolite modified separator for high performance lithium sulfur batteries.From physical properties such as thermal stability,mechanical properties and contact angles of separators,to electrochemical properties such as electrochemical impedance,lithium ion migration number and battery cycle performance,the influence of sepiolite on the electrochemical performance of lithium-sulfur batteries is explored experimentally and theoretically.In this work,a sepiolite modified conductive separator is prepared by blade casting the slurry of dehydrated sepiolite particles and Super C45 on a commercial Celgard 2500separator.Compared with reference conductive separator,the sepiolite modified separator not only upgrades mechanical properties,electrolyte compatibility and thermal stability,but also significantly increases the lithium-ion mobility,improves cycle and rate performances and inhibits self-discharge of lithium-sulfur batteries.A low sulfur-loading(1.5 mg cm^-2)cathode with the sepiolite modified separator delivers a high initial capacity of 1231 m Ah g^-1 at a current density of 2 m A cm^-2.A high loading(5.1 mg cm^-2)lithium-sulfur battery retains a capacity of 848.1 m Ah g^-1 after 100 cycles.Besides,after a 15-day rest,self-discharge of the lithium-sulfur battery decreased to 19.84%.By evaluating the interaction with polysulfides in sepiolite channels and analyzing the diffusion barrier of lithium ions in pore channels with density functional theory calculations,we reveals that the sepiolite blocks polysulfide shuttling and the abundant nano-pore structures in sepiolite promote rapid transport of lithium ions,thus suppressing lithium dendrite growth.In summary,the bifunctional sepiolite modified separator effectively limits the shuttle of polysulfides in the electrolyte,inhibits the growth of lithium dendrites in the negative electrode,and thus improves the cycle and rate performance,cycle life and safety of the lithium-sulfur batteries.In this work,we provide new design concepts of functional separators for inhibiting the polysulfide shuttle effect and lithium dendrite growth in lithium-sulfur batteries.