MOFs-Derived Carbon Materials Anode For The Lithium-Ion Capacitors

Lithium ion capacitors（LICs）draw great attention due to its higher energy density than electronic double layer capacitors,as well as higher power density and cycle life than lithium ion batteries.Typical LICs consists of a capacitor-type cathode and a pre-lithiated anode.However,the sluggish redox reaction of the negative electrode is not matched by the fast adsorption/desorption process of the positive electrode and the power density of LICs is restricted by the anode material.Thus,development of anode with superior rate capability and cathode with high capacity is of great significance for boosting the performance of LICs.Metal-organic frameworks（MOFs）have become ideal precursors for preparing porous carbon due to the rich and adjustable properties of metal nodes,ligands and topological types.In this paper,a rigid ligand（2,7-bis（3,5-dimethyl）dipyrazol-l,4,5,8-naphthalenetetratetracarboxydiimide,H₂NDI）is used to synthesize triply-interpenetrated Co-MOF.Then,the MOF-derived porous carbons were prepared through carbonization of precursor and washing by HCl solution.The effects of carbonisation temperature and metal node ratio on LIC performance were explored.The main contents are summarized as follows:（1）Herein,a rigid ligand（2,7-bis（3,5-dimethyl）dipyrazol-l,4,5,8-naphthalenetetratetracarboxydiimide,H₂NDI）is used to synthesize triply-interpenetrated Co-MOF.Then,the MOF-derived porous graphitic carbons（PGCs）were prepared through carbonization of precursor at different temperatures（900℃,1100℃,1300℃）and washing by HCl solution.The high density of metal ions in interwoven packing structure not only acts as an efficient pore-forming agent,but also promotes in-situ catalytic graphitization of the carbon skeleton during carbonization.Due to the optimized graphitization degree and porous structure,as-prepared PGC-1300 exhibits both high plateau capacity and high-rate performance.Furthermore,LIC PGC-1300//AC is assembled with pre-lithiated PGC-1300 as anode and AC as cathode,delivering a high energy density of 102.8 Wh kg^-1,a high power density of 6017.1 W kg^-1and a cyclic retention of 93.6%after 5000 cycles at 1 A g^-1.（2）Based on the previous section,a series of isomeric bimetallic MOFs(Zn_xCo_100-x-MOFs)with various Zn/Co ratios were successfully synthesized by adding different ratios of Zn/Co salts to the synthesis solution while maintaining the original structure During the carbonisation of Zn/Co-MOF at 800℃,a range of porous carbon materials(Zn_xCo_100-x-PCs)with varying degrees of graphitisation and pore architectures were prepared.The Zn₈₀Co₂₀-PC exhibits proper graphitization degree,high specific surface and abundant pore structure,which provides convenient channels for lithium ion and electron transport to facilitate lithium ion storage.The Zn₈₀Co₂₀-PC shows a high reversible capacity 397.1 m Ah g^-1 at 0.1 A g^-1,and excellent rate capability(109.6 m Ah g^-1 at 1.6 A g^-1).In addition,Zn₈₀Co₂₀-PC also exhibits excellent cycling performance due to its partially graphitic structure(316.6 m Ah g^-1 after 300 cycles at 0.2 A g^-1).Furthermore,LIC Zn₈₀Co₂₀-PC//AC is assembled with pre-lithiated Zn₈₀Co₂₀-PC as anode and AC as cathode,delivering a high energy density of 123 Wh kg^-1,a high power density of 7150.3 W kg^-1and a cyclic retention of 90%after 5000 cycles at 1 A g^-1.