| With the development of portable electronic devices and widespread use of EVs,as the main part of power system,lithium-ion batteries are required to provide higher capacity,longer cycle life,lower cost,and so on.To meet the requirements,the key point is to develop high performance electrode materials.While the anode material nowadays used for lithium-ion batteries is graphite,which shows low energy density.Therefore,high-capacity anode materials are urgent to develop for replacing graphite materia.Basing on conversion reaction,metal compounds could provide considerable capacity as well as high energy density.While the volume change during reaction limits actual performance,designing structure with a buffer environment could solve this problem.In addition,limiting by natural abundance of lithium and cobalt,cost of lithium-ion batteries is hard to reduce,which may throttle the scale application,especially for energy storage power station systems.Cost advantage by high natural abundance of potassium,potassium-ion batteries have drawn interests,and thus developing applicative electrode materials are important.Carbon coating has been regarded as an effective strategy to solve volume change as well as improving the conductivity.Hence,metal compounds/carbon composite material could keep high capacity of metal compounds as well as high stability.And the point is to ensure the homogeneous coating,thus the best way is in-situ coating.Connecting by metal ion center and organic linkers,Metal-organic frameworks(MOFs)materials show high porosity with 3D structure.During the thermal process of MOFs precursor,the organic linkers could form in-situ carbon coating and the metal center can be separated by carbon without agglomeration.So,using MOFs materials as precursor or self-template,we synthesized metal compounds/carbon composite materials and investigated their electrochemical performance as anode material for LIBs.Benefiting from lower cost and considerable energy density,potassium-ion batteries have been regarded as the next generation battery.Graphite could also be used as anode for PIBs with appreciable capacity.Hitherto,reported carbonaceous materials display low capacity and short cycle life,which is far away from ideal condition.In this paper,MOFs derived carbonaceous materials have been synthesized and invested as anode material for KIBs.The main contents as following:1.Using MOFs as precursor or self-temp late as well as facile thermal or chemical etching process,we synthesized metal compounds with in-situ carbon coating.The as-made product has porous hierarchical structure.One side,porosity and high specific area ensure sufficient contact between electrode and electrolyte and reduce ions'diffusion distance,on the other side,hierarchical structure and carbon coating could buffer volume change,thus structure stability could be improved.As a result,as-made samples show excellent capacity performance and long cycle life as anode for LlBs.For example,after 50 cycles at a current density of 100 mA g-1,porous MoO2@C electrode could provide a reversible capacity of 1442 mA h g-1;and CoxP-NC-800 electrode could still maintain 550mAhg-1 of reversible capacity after 1800 cycles at a current density of 1 A g-1.In addition,these works also provide a facile and efficient way to synthesize high-performance anode material.2.We synthesized nitrogen/oxygen co-doped mesoporous carbon by using MOFs as precursor.Porous structure could decrease diffusion distance for ions and the enlarged interspacing could accelerate the intercalation of potassium.What's more,DFT results prove that the introduce of heteroatom not only enhance the conductivity,but also raise the carbon layers' absorption process for potassium atom.Results display that at a current density of 0.05 A g-1,the as-synthesized product can provide high reversible capacity of 364 mA h g-1 after 50 cycles,and even at a current density of 2 A g-1,electrode materials can provide 80 mA h g-1 after 3000 stable cycles. |
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