Preparation And Properties Of Multifunctional Biomass Binder For Lithium-sulfur Battery

Lithium sulfur（Li-S）battery is deemed as one of the most promising next-generation energy storage systems due to the high theoretical specific capacity up to1675 m Ah g^-1,abundant reserves of active substance sulfur,low cost,and environmental friendliness.However,the notorious polysulfide shuttle effect,the volume effect of electrodes in electrochemical reactions,and the insulation characteristics of S and the product Li₂S lead to low Coulombic efficiency and fast capacity decay,limiting the practical application of Li-S batteries.The binder is important component of electrodes,and the related improvement is expected to enhance the electrochemical performance of Li-S battery.Therefore,this work aims to limit the shuttle effect of lithium polysulfide,reduce electrode volume changes,and ultimately improve the electrochemical cycling performance of Li-S batteries from the perspective of preparing binders.The main contents are as follows:In the first part,a sugar based multifunctional binder（PLG）with a three-dimensional network structure is prepared.The multifunctional binder is in situ generated through hydrogen bonding interactions between polyacrylamide（PAM）,locust bean gum（LBG）,and gelled gum（GG）,and its cross-linked structure helps to suppress the variation of electrode volume.The abundant hydroxyl/amino groups in the main chain can effectively anchor polysulfides and inhibit the shuttle effect.Through in situ impedance spectroscopy analysis,it is found that the PLG electrode greatly promote the redox reaction kinetics of battery.It is worth noting that the discharge capacity of PLG electrode is 623.4 m Ah g^-1 after 200 cycles at the rate of 0.2 C(1C=1675 m A g^-1),almost twice that of the PVDF electrode(342 m Ah g^-1).When the load is increased to 2.5 mg cm^-2,the initial capacity can reach up to 1392 m Ah g^-1 at0.2 C.In addition,the capacities of PLG electrode at 60 and 0℃ are 1579.7 and 904.5m Ah g^-1,respectively.The above results indicate that multifunctional PLG binders are beneficial for solving problems in Li-S battery,and can bring overall performance improvement even in extreme working environments,demonstrating enormous application potential in Li-S battery.Polysulfide radical anions are critical components of polysulfides and are often overlooked in the research on the inhibition of shuttle effects.Therefore,in order to further study the polysulfides variation in Li-S battery and the reaction mechanism of polysulfide radical anions,lipoic acid is selected as an effective component for capturing polysulfide radical anions,and is further grafted into polylysine molecular skeleton with the large number of amino and carboxyl groups through method of amidation reaction.Lipoic acid-polylysine biomass binder（LYS-LA）with double capture function of polysulfide radical anions and lithium polysulfide.The amino group in LYS is located on the side chain of the molecule,with a small steric hindrance,is expected to exert excellent lithium polysulfide capture and adhesion performances.Electron Paramagnetic Resonance（EPR）testing analyzes the presence and the composition of polysulfide radical anions,confirming the effective role of LYS-LA to capture free radicals.Meanwhile,the LYS-LA based Li-S battery also exhibits excellent electrochemical performance.At the current density of 0.2 C,a specific capacity of984.8 m Ah g^-1is remained after 200 cycles,with an average Coulombic efficiency of99.7%.At 2 C,LYS-LA electrode still provide a high specific capacity of 715.2 m Ah g^-1.At the temperature of 0℃,the initial specific capacity of LYS-LA electrode is 891.7m Ah g^-l（0.1 C）.After 200 cycles,the discharge capacity is 632.3 m Ah g^-l.It can be seen that LYS-LA binder is facile to improve battery performance.This work fully demonstrates the feasibility of achieving free radical capture through binder design,which helps deepen the understanding of the theory of polysulfide shuttle and broaden the solutions for polysulfide shuttle.