| Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their high power/energy density and long-term cycling stability.Lithium organic molecules with electrochemical activity C=O are promising alternative electrode materials for portable electrochemical storage devices.However,due to their inherent solubility and electronic conductivity problems,they have low capacity,short cycling life and poor rate performance.In this paper,a series of terpyridine-based polycarboxylates and their supramolecular complexes were designed and synthesized,and used as anode materials for lithium-ion batteries.It was found that these materials have high specific capacity,long cycling life and excellent rate performance.The specific research content includes the following four aspects:(1)The coordination-driven stoichiometric self-assembly strategy was used synthesize the novel lithium-rich iron supramolecular compound(LiFeTPYTA)(TPYTA=[2,2':6',2''-terpyridine]-4,4',4''-tricarboxylic acid).The compound contains-[tpy-Fe(II)-tpy]-node and conjugated aromatic carboxylate-Li.Upon application as an anode material in lithium-ion battery,LiFeTPYTA delivered the discharge capacity of714.7 and 543.3 mAh g-1at the current density of 40 and 100 mA g-1after 100 cycles,respectively.And the coulombic efficiency is close to 100%,and the reversible capacity is three times of the reported Li-containing organic compounds.On the basis of XPS,CV and some control experiments,the possible redox mechanism of LiFeTPYTA was proposed.The synergistic effect among lithium salts,?-conjugated tpy-based polycarboxylate and Fe(II)center are an important reason to improve the electrochemical performance of LiFeTPYTA.(2)Two new organic salts(Co1.5TPYTA and Ni1.5TPYTA)have been synthesized by the stoichiometric reaction of lithium terpyridine polycarboxylate(Li TPYTA)with cobalt nitrate/nickel nitrate.The electrochemical performance test shows that Co1.5TPYTA and Ni1.5TPYTA anode materials have high reversible capacity,excellent cycling stability and rate performance.For example,the Co1.5TPYTA anode provides a stable discharge capacity of 973.5 mAh g-1at a current density of 100 mA g-1 after 200cycles,with a coulombic efficiency of 99.8%.The discharge capacity of 308.3 mAh g-1is maintained even when the current density is 1 mA g-1.The mechanism of multi-electron redox reaction in Li-ion batteries and the high degree of lithiation are the main reasons of high electrochemical performance.(3)CoFeTPYTA and NiFeTPYTA were synthesized by the stoichiometric reaction of lithium-rich iron suparmolecular compound(LiFeTPYTA)with cobalt nitrate/nickel nitrate and introducing different valence changing metal centers into the terpyridine-based polycarboxylic acid ligands.The electrochemical performance test showed that CoFeTPYTA and NiFeTPYTA anode materials have high reversible capacity,excellent cycling stability and rate performance.For example,when the current density is 100 mA g-1,the CoFeTPYTA and NiFeTPYTA electrodes provided stable discharge capacity of 1063.0 and 909.6 mAh g-1after 200 cycles,respectively,and the coulombic efficiency is close to 100%.The discharge capacity of 383.7 and192.7 mAh g-1 are maintained even at the current density of 1 mA g-1.The mechanism of the multi-electron redox reaction in Li-ion batteries and the different electrochemical properties with the reaction of different metals and ligands were explained by XPS and CV analysis.(4)A 4-pyridine functionalized terpyridine polycarboxylic acid ligand was designed and synthesized,and an iron supramolecular complex(Fe(HTPYPA)2[HTPYPA=4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylate])was synthesized by using the coordination-driven self-assembly strategy.The discharge capacity of Fe(HTPYPA)2 is 492.3 mAh g-1 at the current density of 100 mA g-1after100 cycles and the coulombic efficiency is close to 100%.The mechanism of redox reaction in Li-ion battery was studied by XPS and CV analysis. |
PDF Full Text Request