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Wuhan University Deng Hexiang & Ke Fusheng Angew. Chem. Int. Ed. : MOFs Is Used For Lithium Sulfur Batteries With High Charge And Discharge Rate

- Dec 14, 2018 -

As a new type of porous material, metallic organic framework material (MOFs) has high porosity and specific surface area, and its application potential in the storage, separation and release of gas molecules has been widely studied.Theoretically, the porous properties of MOF can be used for electrochemical energy storage. However, MOFs usually has poor conductivity, so its application potential in electronic devices and energy storage has not been fully developed.As a new green energy storage technology, li-sulfur battery has a bright application prospect in the field of super-micro battery.The improvement of MOFs conductivity and the demand of high charging-discharge ratio for high-performance li-sulfur batteries provide new methods and ideas for the development of new energy storage technology.

Deng Hexiang recently, wuhan university, professor, associate professor, fu-sheng ke (corresponding author) jointly led the research team, after more than four years of trial and error, developed a MOFs with conductive polymer polypyrrole (ppy) composite material -- ppy - MOF, allows MOFs conductivity increase 5-7 orders of magnitude, and the preparation of low cost, suitable for mass production.The ppy-mofs composite was applied to the sulfur positive electrode carrier material of li-sulfur battery, which perfectly combined the polarity and porous advantage of MOFs and the conductive properties of conductive polymer, and discussed the influence of different pore structure of MOFs on the battery performance.For the first time, the relationship between channel geometry and high magnification performance is explained.Among them, the pcn-224 with interconnecting permeable pores and channels stands out at up to 16.8 under the charge-discharge current density of A g-1, ppy-pcn-224 / S electrode can be up to 670 and 440 mAh·g-1 respectively after 200 and 1000 cycles.The research results provide theoretical guidance for the design of the next generation of new battery energy storage electrode materials, and expand the application prospect of MOFs in electrochemistry.The result, "metal-organic Frameworks for high-charge -Discharge Rates in lithium-sulfur Batteries", was published in Angew.Chem.Int.Ed.And select VIP and cover articles.Jiang haoqing, a doctoral student at wuhan university, and liu xiaochen, a master's student, are co-authors of the paper.


Advantages of ppy-MOF

A) three criteria that high-performance li-s batteries should meet: porosity, polarity, and electrical conductivity. Ppy-mof can integrate the above characteristics.

B) compared with other common sulfur carriers (original MOF, porous carbon and ppy), ppy-mof structure is able to store polysulphides with better performance of ion diffusion and electron transfer.


Preparation, morphology and conductivity of ppy-s-in-MOF structure

A) preparation process of ppy-s-in-mof structure;

B-D) SEM images of crystals pcn-224, s-in-pcn-224 and ppy-s-in-pcn-224 (ruler 500 nm);

E-G) SEM images of mil-101, s-in-mil-101 and ppy-s-in-mil-101 crystals (scale 200 nm);

H) haadf-tem images of ppy-s-in-mil-101;

I-l) element distribution of ppy-s-in-mil-101;

M) electrical conductivity of the structures of MOF and ppy-s-in-mof;

N) ppy-MOF, MOF, ppy and porous carbon were used as sulfur carriers, 0.Under 2 C, ppy-mof structure has the best inhibitory effect on the shuttle of polysulfide.


Electrochemical properties of ppy-s-in-MOF structure

A) the key influencing factors for charging the battery at high and low magnification. The size of the circle indicates the importance of the factors;

B, C) the battery of ppy-s-in-mil-53, s-in-mil-53 and ppy-s is from 0.1, C to 1.The multiplier property of 0 C and its 1.The corresponding cycle performance of 100 cycles under 0 C;

D) ppy-s-in-pcn-224 and s-in-carbon from 0.5, C to 5.The multiplier property of 0 C;

E) 5.S-in-carbon electrode and 5 at 0 C.0, 10.GDC curve of ppy-s-in-pcn-224 electrode after 400 charge-discharge cycles under 0 C;

F) 5.The cycling performance of ppy-s-in-pcn-224, ppy-s-in-mil-53, ppy-s-in-mil-101 and s-in-carbon electrodes under 0 C;

G) 10.The long-term cycling performance of ppy-s-in-pcn-224 electrode under 0 C, and the coulomb efficiency was indicated by the gray point.


Structure of MOF and ion diffusion path

Crystal structures of pcn-224, mil-53 and mil-101 and their corresponding ion diffusion paths.Compared with the discontinuous channel of mil-53 and the 3D graded cage channel of mil-101, the crosslinked channel of pcn-224 can conduct ion diffusion more effectively.

The pore structure of porous electrode material plays an important role in the ion diffusion velocity, which affects the battery performance.The ppy-mof composite prepared by this work provides a new way to solve the conductivity problem of MOFs, and thus gives full play to the advantages of the polarity and porosity of MOFs in li-sulfur batteries.Studies have shown that MOFs with shorter ion migration paths and larger pore sizes are most suitable for li-s batteries with high magnification and long cycle.The research also opens up the prospect of electrochemical applications of MOFs.