Preparation And Lithium Storage Properties Of Tin-based Metal-organic Frameworks

With the rapid advancement of global technology,society has increasingly demanded higher performance for energy storage devices.Commercial lithium-ion batteries are bottlenecked due to the low theoretical capacity of graphite cathodes.Therefore,researchers are exploring various aspects to solve the above problems.In this paper,two strategies are chosen to start the research with Sn-based MOF materials as the main body:first,to study other new energy storage devices such as lithium-selenium batteries;second,to explore a new anode material that can replace graphite materials,such as tin-based materials.Metal-organic framework materials have received a lot of attention from researchers due to their simple preparation,structural adjustment,high-proportioned surface area.Currently,MOFs exhibit superior electrochemical performance in various energy storage devices.In this thesis,tin-based metal-organic frameworks were studied and selenocarbon composites were prepared by argon calcination,acid etching and Se compounding to alleviate the shuttle effect of lithium-selenium batteries;different structures of tin-based MOF materials were also prepared by adjusting organic ligands and were directly used in lithium cathodes to improve the volume expansion and electrode pulverization of tin cathode materials.The specific study is divided into the following three parts:(1)The most studied Sn-PPA material was selected for calcination and acid etching to obtain carbon material,and then compounded it with Se to obtain the Se/C composite.The capacity of the Se/C material was 82 m Ah g^-1 after 100 cycles at a current density of 1 A g^-1,which was much better than that of the Se electrode at 23 m Ah g^-1.This indicates that the Se/C composite can be prepared to effectively alleviate the shuttle phenomenon of Se and thus improve the cycling performance.(2)One-step synthesis of Sn-PPA material by solution method using terephthalic acid as organic ligand,which is directly used as anode material for lithium-ion batteries.Thanks to the reversible Sn-O bonding,the material exhibits a cycle life that far exceeds that of Sn O₂/C materials,maintaining a discharge capacity of 663 m Ah g^-1 after 400 cycles at a current density of 1 A g^-1.This indicates that the Sn center can be immobilized onto the carboxyl group of terephthalic acid by preparing tin-based MOF material,thereby effectively relieving the volume expansion effect of the tin based material.(3)We used isophthalic acid and phthalic acid as organic ligands to synthesize Sn-MPA and Sn-PA materials,respectively.When used directly as anode materials for Li-ion batteries,Sn-MPA and Sn-PA materials exhibit excellent cycle stability and extremely high discharge specific capacity.The Sn-MPA and Sn-PA materials maintain high discharge specific capacities of 1024 m Ah g^-1 and 1104 m Ah g^-1 after 400 cycles at a current density of 1 A g^-1.This indicates that the structure and specific surface area of the Sn-based MOF material can be changed by changing the organic ligand,thus effectively increasing the discharge capacity.