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Advanced materials: hard carbon nanosheets with uniform concentrated polar micropores and contactable functional groups for high performance sodium ion storage

wallpapers Cruise 2020-08-04

is rich in sodium resources low cost so sodium ion battery is considered to be one of the most promising large-scale energy storage technologies. Among them hard carbon anode composed of a large number of graphite microcrystals defects pore structure has attracted much attention in practical application. In recent years there are many reports about the hard carbon with high graphitization degree porous hard carbon. Their specific capacity is 200 ~ 500 mahg-1 the first coulomb efficiency is 30% ~ 80%. Due to the diversity of active sites the complexity of sodium storage behavior in these hard carbons it is difficult to take into account the above three key electrochemical indicators the corresponding potential regions have always been controversial. If the active sites in hard carbon can be controlled uniformly it will be helpful to explore the behavior of sodium storage. The introduction of pores into hard carbon can effectively reduce polarization improve the diffusion kinetics of sodium ions. However due to the lack of effective methods to control the pore size the irreversible capacity loss of porous hard carbon is large ice is low during the first charge discharge process. The total potential range of sodium storage is between 0 3.00 V the capacity below 1.00 V contributes to the energy density but it is usually less than 50% of the total capacity. In addition carbonyl hydroxyl groups can participate in the redox reaction chemical adsorption of sodium ions which is conducive to the rapid storage of sodium on the surface but also has the problem of low available capacity. Through the design synthesis of hard carbon materials with specific pore structure surface functional groups it is expected to solve the bottleneck problem. Lu Hui's "spkds" "spkd 1.5" hard carbon with uniform pore size distribution were synthesized by using the "spkds" "spkds" methods. The results show that the micropores are conducive to the rapid transport of sodium ions inhibit the contact between the electrolyte the inner surface of the micropores which can improve the rate performance the first coulomb efficiency of the hard carbon anode at the same time; the surface redox reaction chemical adsorption process of carbonyl hydroxyl groups are conducive to the rapid capacitive storage of sodium. Based on this special combined structure design the hard carbon can show high capacity (318 MAH) g-1@0.02 A g-1) excellent rate performance (145 MAH) g-1@5.00 A g-1) up to 95% of the available capacity (below 1.00 V potential) a new sodium storage mechanism of "double potential platform" is presented. The mechanism of sodium storage in the two potential plateau regions during charging was investigated by CV GITT XPS in-situ XRD. The low potential plateau region (0.01 ~ 0.10 V) is the desalting of sodium ions from the graphite layer; the high potential plateau region (0.40 ~ 0.70 V) corresponds to the desalting process of carbonyl hydroxyl functional groups on the surface. The related achievements were published in advanced materials under the title of "hard carbon nanosheets with uniform ultramicropores accessible functional groups showing high real capacity superior rate performance for sodium ion storage"( DOI:10.1002/adma.202000447 )It's on.

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