Preparation And Performance Of Gel Polymer Electrolyte For Quasi-solid State Lithium-Sulfur Batteries

Lithium-sulfur battery?LSB?has become increasingly attractive in the field of high energy battery due to the high specific capacity.At the same time,sulfur is abundant,cheap and environmentally friendly,which gives more significance to its study.However,in the liquid state LSB,the shuttle effect of polysulfide will hugely harm its cycle stability and longevity,which will impede the further development of LSBs.However,Using gel polymer electrolytes?GPEs?instead of commercial separator can not only increase the safety of the battery,but also effectively increase the ionic conductivity,inhibit the shuttle of polysulfide and hinder the growth of lithium dendrite,which will significantly improve the comprehensive performance of LSBs.Herein,in order to improve the electrochemical performance of LSBs and promote its commercialization,double-layer electrolyte membrane,3D electrolyte membrane polymerized via ultraviolet and electrolyte membrane with"core-shell" structure were prepared respectively.And the ionic conductivity,Li⁺transference number were tested.At the same time,LSBs were assembled,and their electrochemical performance were also studied systematically.?1?In order to optimize the interface performance of electrolyte and Li anode,a double-layer electrolyte membrane composed of a high conductivity layer and a transition layer is designed,which contact the positive electrode and the negative electrode respectively when assembling the battery.The high ionic conductivity layer is composed of polyacrylonitrile?PAN?and Li_1.3Al_0.3Ti_1.7?PO₄?₃?LATP?.PAN has high intrinsic ionic conductivity.Using it as the polymer matrix of the layer can fully leverage its high ionic conductivity and guarantee the electrochemical performance of the GPEs.However,pure PAN will cause the"passivation effect" of Li anode.Therefore,the layer contacting the anode is a transition layer with different components,which is composed of PAN,polyethylene oxide?PEO?and LATP.The addition of PEO can effectively weaken the"passivation effect" and protect the Li anode.As a result,the LSBs assembled with the double-layer GPE have the initial discharge capacity of904 mAh g^-11 at the current density of 0.1C.After 100 cycles,its capacity retention is79.0%,exhibiting the obviously improved electrochemical performances.?2?Ultraviolet polymerized GPEs were fabricated with two polymer matrices,in which the ultraviolet polymerized pentaerythritol tetraki-divinyl adipate?PETT-DA?is the 3D polymer matrix and polyvinylidene fluoride-hexafluoropropylene?PVDF-HFP?is the codoped polymer matrix.Simultaneously,the multi-walled carbon nanotubes?MWCNTs?served as the nanofillers can form different hydrogen bonds with PETT-DA and PVDF-HFP,which can further improve its comprehensive performances.For the assembled LSBs,at the current density of 0.5C,the initial discharge capacity can reach to 705 mAh g^-1.After 300 cycles,it has the capacity retention of 86.4%,demonstrating the elevated electrochemical performances.?3?GPEs with "core-shell" structure were fabricated via two steps:electrospinning and ultraviolet polymerization.The"core" was the electrospun membrane substrate,which was composed of PVDF-HFP and PEO.And the"shell" was the ultraviolet polymerized PETT-DA,coating on the outside.Meaningfully,inner porous electrospun membrane can provide the high electrolyte uptake rate,therefore,guaranteeing the high ionic conductivity and Li⁺transference number.Outside PETT-DA has the carbonyl groups,which can interact with lithium polysulfides and suppress the shuttle effect.As a result,the assembled LSBs have the initial discharge capacity of 543 mAh g^-1 at the high current density of 2C,with the capacity retention of 87.1%after 300 cycles,displaying the excellent electrochemical performances.