Host-guest Interaction Design Of Functional Metal-organic Framework Materials And Their Application In Lithium Metal Batteries

Due to the high theoretical specific capacity(3860 m Ah g^-1),low working potential（-3.040 V）,and low density(0.59 g cm^-3),lithium metal batteries with lithium metal as anode can match with various cathode materials and have become an important research object to solve the mileage anxiety of secondary batteries.Currently,the main problem of lithium metal batteries is how to improve the energy density and cycle life under the premise of ensuring its safety.The safety of lithium metal batteries can be achieved through the development of solid-state lithium metal batteries made of solid electrolytes（SEs）.Besides,lithium-sulfur batteries（LSBs）which are one of the most promising solutions for obtaining higher energy density.The main difficulty in the study of solid-state batteries（SSBs）lies in the research and development of SEs with high ion transport,while the main problem of LSBs is how to solve the capacity reduction and life degradation caused by the diffusion（shuttle effect）of soluble lithium polysulfide（Li PSs）.Both of these problems involve the diffusion and conduction of ions in lithium metal batteries.The metal-organic framework（MOFs）is chemically designable and structurally diverse,which is expected to achieve precise design of ion conduction and diffusion processes through the regulation of the interaction between the host and the object.Based on this,the MOFs-based SEs and sulfur host materials were developed by designing the channel structure and chemical environment of MOFs to realize the high-efficient lithium-ion conduction and the inhibition of Li PSs shuttle effect.The main research contents are as follows:（1）The concept of construction of continuous ion-conductive paths in SSBs via cross-linked MOF chains is proposed.Firstly,a newly developed MOF（Zr-BPDC-2SO₃H）was prepared.The high-density of-SO₃H groups can interact with the guest molecule Li⁺to promote ion conduction and improve its single-ion conduction ability.Then MOFs nanoparticles were continuously grown on the bacterial cellulose（BC）nanofibers to obtain cross-linked MOF chains.Excellent single-ion conductivity(t⁺_Li=0.88),low interfacial resistance（74Ω）,wide electrochemical window（5.10 V vs Li|Li⁺）,and excellent Li dendrite suppression were achieved.Li Fe PO₄/Li SSB with high active material loading of 14.6 mg cm^-2 and high-voltage Li Co O₂/Li SSB both exhibited excellent performances.（2）A MOF-sulfur copolymer（CNT@Ui O-66-V-S）was prepared as a cathode material for LSBs by copolymerizing guest molecule S₈ with vinyl-functionalized MOFs（Ui O-66-V）by inverse vulcanization to accelerate the redox kinetics and ameliorate shuttle effects.The MOF-sulfur copolymer cathode exhibits a low decay rate of 0.028%per cycle during 1000cycles at 1 C and also achieves stable cycling under a high sulfur loading of 5.6 mg cm^-2 at0.2 C.During the charge/discharge process,a radical reaction mechanism was presented in MOF-sulfur copolymer cathode,different from that of the traditional composite sulfur cathode,which promotes the conversion of Li PSs and effectively inhibits the growth of lithium dendrites.（3）A micro-nanoreactor（Ti O₂-in-101（Cr））with a high density of catalytically active sites was designed as a sulfur host material for LSBs.Benefiting from the synergistic effect generated by the host-guest interaction between the Ti O₂ in the pores and the MOFs matrix,Ti O₂-in-101（Cr）shows abilities to promote the conversion of Li PSs and achieve faster charge transfer capability and ion transport efficiency,enhancing the redox kinetics of LSBs.Finally,the LSBs assembled with Ti O₂-in-101（Cr）@S as the cathode achieve excellent rate performance,cycling stability at high C-rates,and high areal specific capacity under high sulfur loadings up to 8 mg cm^-2.