Studies On The Preparation And Performance Of Binders For Lithium-sulfur Batteries

The lithium-sulfur?Li-S?battery has been considered as a good candidate to current LIBs,since it delivers an ultrahigh theoretical energy density of 2567 Wh kg^-1,5 times higher than that of current LIBs,and very low cost.Noted that huge volume expansion,the insulator nature of sulfur active materials?S/Li₂S?and rapid capacity fade owing to polysulfide shuttle during charge-discharge processes limit the practical applications of Li-S batteries.To counteract these shortfalls,rational design of advanced polymer binders has aroused increasing attentions.It is well known that pectin possess abundant polar groups?eg.carbonyl and hydroxyl groups?,and thus deliver interactions with polysulfides via ion-dipole interactions for suppressing the polysulfide shuttle.Therefore it has the potential to be a sulfur cathode binder,but it has not been reported before.Based on the above ideas,Pectin was firstly used as the cathode binder of lithium sulfur battery,and the discharge capacity for the first time was up to 1210.6 mAh g^-1 and there was still 837.4 mAh g^-1 discharge capacity after 200 cycles,superior to that of the CMC-SBR counterpart.Sodium carboxymethyl cellulose?CMC?has been widely used as a sulfur cathode binder,but its cycling performance still cannot meet the practical application requirements in Li-S batteries.We consider that the reason of the poor cyclic performance in CMC should blame the insufficient adsorption capacity to inhibit the polysulfide shuttle effect in that the carboxyl groups and hydroxyl groups in CMC can only interact with the polysulfide anions to form ion-dipole interactions.Given that quaternary ammonium salt with negatively charged sulfide anion can form strong electrostatic interactions,which are stronger than the ion-dipole interaction in CMC,therefore,the blend of poly?quaternary ammonium salt?and CMC,might possess the enhanced ability to capture polysulfide compared with CMC and thus is expected to further improve the cycle performance of Li-S batteries.Therefore,the properties of CMC and polyquaternium-28mixed binder were studied.The study found that the mass ratio between CMC and polyquaternium-28 was 1:1,which the electrochemical performance was the best.And the discharge capacity of up to 965 mAh g^-1 was obtained when the current of 0.5C was used for the cycle and still remaining discharge capacity of over 600 mAh g^-1 after 150 cycles.