Novel Lignin Based Aqueous Binder For Lithium-sulfur Batteries

Lithium sulfur?Li-S?batteries are regarded as the potential candidates for the next generation secondary batteries owing to their high gravimetric energy density(2600 Wh kg^-1),inexpensiveness,and eco-friendliness.However,there are still several barriers in Li-S batteries,such as the insulativity of sulfur,the large volume expansion and the nonnegligible shuttle effect from soluble polysulfides,which impede their commercial application.Functional binders can not only assist the electrode forming and structure preserving but also benefit high electrochemical performance.In this study,we explored the feasibility for directly introducing the pulping waste as ecofriendly and effective binder for Li-S batteries,and also synthesized poly?3,4-ethylenedioxythiophene?/lignosulfonic acid?PEDOT/LSA?conductive binder to further improve the cycle stability and rate performance.Specific contents are listed as follows:We first used the lignosulfonate as aqueous binder for Li-S batteries,and investigated the performance difference between sodium lignosulfonate?LSNa?and calcium lignosulfonate?LSCa?.The LSCa-based electrode retains a capacity of 453mAh g^-1 after 500 cycles at 1C(1C=1675 mA g^-1)with a capacity retention of 50.84%,which are much better than those of PVDF-based electrode.Furthermore,a preferable areal capacity of 4.16 mAh cm^-2 is obtained after 100 cycles at 0.05C with a high sulfur loading of 7.64 mg cm^-2.These achievements are ascribed to the better absorption ability to polysulfides,more favorable Li⁺transportation and superior adhesion property.Based on the above experiments,we further synthesized a series of PEDOT/LSA complexes,in which LSA worked as dispersant and dopant.The complexes were applied as conductive binder for Li-S batteries.The corresponding PEDOT/LSA complex benefit the batteries best,when the ratio of PEDOT and LSA is fixed at 1:4.Peeling tests show that the average force of PEDOT/LSA-based electrode is 1.8 N,which is much higher than those of LSCa-based and PVDF-based electrodes.The PEDOT/LSA-based electrode retains a capacity of 540 mAh g^-1 after 400 cycles at1C with a capacity retention of 72.97%.It also delivers an excellent capacity of 601mAh g^-1 even at the high current density of 5C.Moreover,a preferable areal capacity of 6.01 mAh cm^-2 is obtained after 80 cycles at 0.05C with a high sulfur loading of10.51 mg cm^-2.These results indicate that PEDOT/LSA binder enhances the cycle stability and rate performance of Li-S batteries.Compared to the PVDF and LSCa,this conductive binder has a better adhesion.Besides,the PEDOT improves the conductivity of electrode.In this study,lignosulfonate was used as cathode binder for Li-S batteries for the first time and derived for PEDOT/LSA conductive binder to further improve electrochemical performance.Our work not only shows the feasibility for introducing the pulping waste as ecofriendly and effective binder for Li-S batteries,but also suggests a facile and sustainable way for the high-value utilization of waste lignin.