Preparation Of Organic Carbonyl Compound Electrode Materials And Their Lithium And Sodium Storage Properties

The use of fossil energy causes global warming and environmental pollution,and there is an urgent need to develop green and sustainable energy systems and energy storage technologies.Lithium/sodium ion batteries are considered the most convenient and effective means of energy storage due to the advantages of being green,pollution-free,and sustainable.The main factor that affects the energy density of lithium/sodium ion batteries is electrode materials.The traditional electrode materials are mainly inorganic,but their theoretical specific capacity and structural stability are not ideal,limiting their practical application in lithium/sodium ion batteries.In recent years,organic materials have become a new choice of electrode materials for lithium/sodium ion batteries for their diverse types,rich resources,convenient access to materials,and clean and sustainable characteristics.Among them,organic carbonyl compounds have attracted researchers’attention owing to their high theoretical specific capacity and controllable structure.However,when organic carbonyl compounds are employed as electrode materials for lithium/sodium ion batteries,they also have some shortcomings that are common to other organic electrode materials,such as high solubility in the electrolyte,which leads to poor cycle stability;The doping degree is low,making the actual specific capacity low;poor conductivity,poor rate performance,etc.Based on this,this article mainly uses organic carbonyl compounds as electrode materials for lithium/sodium ion batteries and improves their shortcomings through polymerization and composite with carbon-based materials.The morphology and structure of the synthesized supramolecular assemblies（SA-1）,poly（2,5-dihydroxyterephthalic acid）,and tetrahydroxybenzoquinone orthodisodium salt/carbon point complexes（o-Na₂THBQ/CDs）were characterized.The electrochemical performance and lithium/sodium storage reaction mechanism of these organic carbonyl compounds were also investigated.The main research is as follows:（1）As an organic carbonyl small molecule compound,pyromellitic acid（PMA）has the characteristics of fast redox reaction speed and high theoretical specific capacity.Herein,a chemical synthesis method was used to synthesize the organic carbonyl small molecule compound PMA into a supramolecular assembly（SA-1）,which was selected as an anode material for lithium/sodium ion batteries to investigate their structural morphology and electrochemical performance.SEM results demonstrated that SA-1exhibited a regular rod-shaped structure.At a current density of 50 m A g^-1 and a voltage range of 0.05～3.0 V,PMA delivered a specific discharge capacity of 455 m Ah g^-1 in a lithium-ion battery after 200 cycles.Under the same conditions,SA-1 exhibited a specific discharge capacity of 578 m Ah g^-1.Subsequently,in the rate performance test,PMA and SA-1 showed a specific discharge capacity of 65 and 95 m Ah g^-1 at a current density of 2000 m A g^-1,respectively.In addition,when tested as anode materials for sodium ion batteries,the discharge specific capacities of PMA and SA-1 were 32.8 and92.1 m Ah g^-1,respectively,after 100 cycles at a current density of 50 m A g^-1.In the high current density of 2000 m A g^-1,the discharge specific capacity of PMA was 25.6m Ah g^-1,while SA-1 delivered a discharge specific capacity of 64 m Ah g^-1.The results suggested that SA-1 performed better cycle stability and rate performance than PMA in the process of being used as an anode material for lithium/sodium ion batteries.Subsequently,we explored the charge and discharge mechanism of SA-1 through ex-situ IR,and the results showed that the reaction mechanism was essentially a mutual conversion process between the carbonyl and enol groups of carboxylic acids.（2）Poly（2,5-dihydroxyterephthalic acid）（PDHTA）was synthesized by polycondensation using 2,5-dihydroxyterephthalic acid（DHTA）as a monomer and employed as an anode material for lithium/sodium ion batteries.SEM results revealed that the polymerized PDHTA exhibited a more regular layered structure.Electrochemical performance tests were conducted at a current density of 50 m A g^-1and a voltage range of 0.1～3.0 V.After 200 cycles,the specific discharge capacity of PDHTA in a lithium-ion battery was 180 m Ah g^-1,which was significantly improved compared with the specific discharge capacity of DHTA(106 m Ah g^-1)under the same conditions.Even after 1000 cycles at a high current density of 480 m A g^-1,the PDHTA still maintained a specific discharge capacity of 88 m Ah g^-1,with excellent cycle performance.In particular,when selected as an electrode material for sodium ion batteries,PDHTA still displayed good electrochemical performance with discharge specific capacities of 81.5 and 43.5 m Ah g^-1 at current densities of 50 and 480 m A g^-1,respectively.Subsequently,we explored the charge and discharge mechanism of PDHTA at 0.1～3.0 V through ex-situ IR.The reaction mechanism was essentially the mutual conversion between the carbonyl and enol groups of carboxylic acids.（3）Small molecule carbonyl compounds can improve their electrochemical performance to a certain extent through salinization,but the effect is not obvious.There are still shortcomings such as high solubility and poor conductivity.Composite with carbon quantum dot materials（CDs）can further optimize their cycle and rate performance.In this section,we obtained tetrahydroxybenzoquinone orthodisodium salt（o-Na₂THBQ）through a simple salinization reaction and then compounded it with CDs after ultrasonic stirring.The results showed that when the composite mass ratio of o-Na₂THBQ to CDs was 20%（o-Na₂THBQ/CDs-2）,the electrochemical performance was the best.As an electrode material for sodium ion batteries,under test conditions with a current density of 50 m A g^-1 and a voltage range of 1.0～3.0 V,the first cycle discharge specific capacity of the o-Na₂THBQ/CDs-2 composite material was 410 m Ah g^-1.Even after 1500 cycles,it still maintained a discharge specific capacity of 182 m Ah g^-1,and the coulomb efficiency was close to 100%during the entire cycle.After 1300cycles at a current density of 500 m A g^-1,the o-Na₂THBQ/CDs-2 composite exhibited a high specific capacity of 63 m Ah g^-1.The charge and discharge process of o-Na₂THBQ/CDs-2 at 1.0～3.0 V was investigated by ex-situ IR.The reaction mechanism was essentially the conversion between carbonyl and enol groups.