Design,Synthesis And Energy Storage Performance Of Oxygenated Conjugated Double Bond Compounds As Anode Materials For Lithium/sodium Ion Batteries

Lithium-ion batteries have been successfully applied to various portable devices and electric vehicles due to their unique advantages such as high capacity and high energy density.In the research of anode materials for lithium-ion batteries,commercial graphite anodes are difficult to meet the requirements of the society for energy storage equipment because of their low capacity.Inorganic anodes often exhibit severe volume expansion during lithium ion insertion/extraction process,resulting in rapid capacity decay.At the same time,the organic negative electrode has attracted extensive attention of researchers due to its molecular structure design,environmental friendliness,and low cost.Moreover,the organic electrode almost shows no obvious volume expansion after discharging.We can design electrode materials with higher capacity and magnification performance through the design of functional groups and adjustment of micromorphology.However,poor conductivity,easy dissolution in electrolytes and exposure of limited active sites have become major challenges for improving the electrochemical performance of organic materials.In view of the inherent shortcomings of organic electrodes,this paper attempts to synthesis the sodium salt of the small molecule to inhibit the dissolution of small molecules in the electrolyte,design the sandwich layered structure to accelerate the deintercalation rate of lithium ions,prepare the nanostructured active particles to obtain the more active sites and construct the porous polymer skeleton to achieve excellent cycle performance.The main content is as follows:(1)In order to reduce the solubility of organic carbonyl anode materials in electrolyte to obtain excellent cycle performance suppress the dissolution of small molecules in the electrolyte,this paper prepared sodium carboxylate(including sodium citrate,sodium tartrate,sodium oxalate and sodium pyromellitic acid)with the small molecule compound that is easily soluble in the electrolyte.When evaluated as an anode material for LIBs,the sodium carboxylate electrodes exhibit high reversible capacities.At a current density of 50 mA/g,sodium oxalate,sodium tartrate,sodium citrate and sodium pyromellitic acid can obtain 619.6 mAh/g,392.3 mAh/g,403.7 mAh/g,and 278.1 mAh/g respectively after 200 cycles.Their capacity retention rates were 179 %,148 %,173 %,108 % respectively.The increase of capacity is mainly due to the cleavage of large electrode active particles to generate more active sites and shorten the diffusion distance of lithium ions during the cycle.(2)Besides,in order to improve the electrical conductivity and the stability of the layered structure of organic conjugated anode materials to obtain excellent rate capacity,we prepared a sandwich layered structure of 4-nitro yttrium phthalocyanine(TNY-Pc)compound with a macrocyclic conjugated structure.XRD and TEM tests show that the interlayer spacing of phthalocyanine molecules was about 0.307 nm and the interlayer spacing after cycling had hardly been changed,which showed excellent structural stability.When used as a negative electrode for lithium batteries,the TNY-Pc electrode exhibits a high reversible capacity of 610 mAh/g at a rate of 140 mA/g after 1,150 cycles.Even at a current density of 3 A/g,it can reach 370.2 mAh/g.The excellent cycle life and rate capacity of this layered phthalocyanine are mainly attributed to the porous and stable conjugated molecular structure and the rich N=O,C=C and other active groups.(3)Moreover,in order to obtain more active sites of exposed organic active substances to obtain high capacity,excellent rate performance and long cycle life,this paper prepared NTCDA organic particles with nanoblocks,nanorods and nanowires shape using electrostatic spinning technology and the compound of porous diatomite.The electrochemical tests show that nanowire NTCDA electrode can still reach 1008.5 mAh/g at a current density of 100 mA/g after 200 cycles,and the capacity retention rate can reach 91.2 %,which is higher than 753.2 mAh/g of the nanorod electrode and 288.1 mAh/g of the nanoblock electrode.When the current density is increased to 1.5 A/g,the nanowire NTCDA electrode can still obtain 508.9 mAh/g.The long cycle life and high rate capacity of this nanowire electrode are mainly due to the larger specific surface area and more exposed active sites,which are conducive to the full penetration of the electrolyte and fast diffusion of lithium ion.(4)Finally,in order to reduce the solubility of organic conjugated electrode materials in electrolyte to obtain excellent cycle performance and rate performance,this paper attempts to graft macromolecular phthalocyanine onto MA-VA polymer to prepare porous polymer MAVA-PcNi.When used in the negative electrode of a lithium ion battery,at 200 mA/g,after 400 cycles,a capacity of 512 mAh/g can be obtained,which can reach the capacity retention rate of 71.5 %.As the negative electrode of sodium ion battery,under 100 mA/g,after 400 cycles,the capacity of 289 mAh/g can still be obtained.The MA-VA-PcNi electrode shows excellent sodium storage performance.This result is mainly due to the intra-molecular multi-frame pore structure of MA-VA-PcNi organic frame polymer electrode materials,which is conducive to the migration of lithium / sodium ions to improve the migration rate of lithium / sodium ions,and the low solubility of the polymer in the electrolyte,which shows excellent cycle stability.