| Lithium-sulfur（Li-S）batteries have attracted great attention due to their theoretical energy density of 2600 Wh kg-1,abundant sulfur resources,and environmental friendliness.However,in practical applications,the dissolution and shuttling of polysulfides can lead to the loss of active materials and the volume change of sulfur during cycling destroys the integrity of the cathode,resulting in a sharp capacity decay.As an indispensable component in the cathode,the binder plays a crucial role in maintaining the integrity and stability of the electrode structure.In view of the above problems,this paper intends to use four different polymer binders containing thiol groups and with a network structure to explore the effects of thiol groups and polar functional groups in the binder on the electrochemical performance of lithium-sulfur batteries.The main research contents and results are as follows:Firstly,ethylene glycol diglycidyl ether（GDGE）and pentaerythritol tetraglycidyl ether（PETGE）were used as raw materials to prepare ethylene glycol diglycidyl ether-dithiocyclic carbonate（GDGE-DTCC）and pentaerythritol tetraglycidyl ether-tetrathiocyclic carbonate（PETGE-TTCC）,and further cross-linked with polyethyleneimine（PEI）to prepare two three-dimensional network polymer binders CAN-T and CAN-F with sulfhydryl groups.The network structure formed between hydrogen bonds and functional groups can resist the volume change of the positive electrode,strengthen the contact between the positive electrode material and the current collector,and improve the utilization rate of sulfur.The interaction between sulfhydryl groups can generate S-S bonds,which further stabilize the positive electrode structure and participate in the discharge process of the battery as an active material.At 0.2 C current density,the initial discharge specific capacities of CAN-F and CAN-T sulfur cathodes reach 1268 m Ah g-1 and 1147 m Ah g-1,respectively,and after 100cycles,95.9%and 86.3%respectively high capacity retention.When the sulfur loading reaches 4.8 mg cm-2,the high-sulfur-loaded cathodes prepared by CAN-F and CAN-T as binders also have good stability.After 60 cycles,the capacity retention rates are 98.5%and94.9%.On this basis,we introduce amide groups on the basis of thiol network structure binder to further strengthen the interaction with polysulfides.N,N’-bis（2-oxothiolan-3-yl）succinamide（BOTS）and N,N’-bis（2-oxothiolan-3-yl）adipamide（BOTA）were prepared by the reaction of DL-homocysteine thiolactone hydrochloride with succinyl chloride and adipyl chloride respectively.and further affinity ring-opening with polyethyleneimine（PEI）to synthesize CAN-S and CAN-L.In addition to containing sulfhydryl and amino groups,the bisamide structure of these two binders enables CAN-S and CAN-L to more effectively hinder the diffusion and shuttling of polysulfides in the electrolyte.At 1 C rate,the cathodes prepared based on CAN-S and CAN-L binders achieve initial discharge specific capacities of 871 and 837 m Ah g-1,and have 83.9%and 62.5%capacity retention after 500 cycles.In addition,at a high sulfur loading of 6.9 mg cm-2,the battery with CAN-S binder can also achieve 89%capacity retention after 60 cycles at 0.1 C.The S/CAN-S cathode exhibits excellent electrochemical performance under the condition of high current density and high sulfur loading,which provides the possibility to construct lithium-sulfur batteries with high energy density and high stability. |
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