Preparation And Lithium/Sodium Storage Properties Of Electrode Materials Based On Small Carbonyl Organic Molecules

Advanced energy storage technology plays an important role for the development of human society.Owing to intrinsic excellent properties of energy storage,lithium ion batteries?LIBs?are widely applied in life and production of society.Nowadays,inorganic materials dominate commercial electrode materials of LIBs.However,energy density,power density,safety property,cost,environmental friendliness,and sustainability of LIBs need to be improved,which will restrict further development and application of LIBs.In comparison with inorganic materials,organic carbonyl electrode materials are getting more and more attention from researchers because of environmental friendliness,renewability,diversity,designability,and definiteness of structures.Small organic carbonyl molecules as electrode materials for LIBs and sodium ion batteries?SIBs?are in the first stage of the research.So,there are several challenges for these materials,such as dissolution problems,poor electronic conductivity,unsatisfying actual capacity,low inital coulombic efficiency and confusing mechanism of lithium-storage and sodium-storage.The dissertation focuses on small organic carbonyl molecules as electrode materials,and meet above-mentioned challenges by chemical modification,in-situ composites,ex-situ characterization,and theoretical calculation.The main content of this dissertation is as follows:1.With respect to serious dissolution problems of chloranilic acid in the organic electrolyte,a new oligomeric sodium salt is prepared by polymerization of chloranilic acid through thioether bonds.Besides,the oligomeric sodium salt?Na₂PDS?is further purified through a simple salification reaction,which endows organic electrode materials with intrinsic insolubility in the organic electrolyte.The ex-situ Fourier-transform infrared spectra?FTIR?and ex-situ dissolution experiments indicate that Na₂PDS is synthesized successfully and intrinsically insoluable in the organic electrolyte.As anode materials for SIBs,the discharge specific capacity of Na₂PDS electrodes is 183 m Ah/g after 150 cycles at a current density of 100 m A/g,exhibiting superior cycling performances.Moreover,Na₂PDS electrodes deliver a discharge specific capacity of 138 m Ah/g after 500 cycles at a current density of 500 m A/g,which shows outstanding cycling performances at high rate because of fast electrochemical kinetics.Furthermore,the sodium-storage mechanism of Na₂PDS was explored by ex-situ FT-IR characterizations.This word demonstrates that chemical modification of small organic carbonyl molecules can efficiently restrain the dissolution in the organic electrolyte,which is beneficial for improving the electrochemical performance of electrode materials.2.The previously reported small organic carbonyl molecules as electrode materials often comprise conjugated structures,whereby adjacent conjugated moieties could distribute partial concentrated negative charges to stabilize the enolic structures,achieving remarkable electrochemical performances.However,the variety of conjugated carbonylcontaining small organic molecules is small,and thus the screening of conjugated carbonylcontaining organic electrodes is limited.Organic carbonyl molecules with non-conjugated structures as electrode materials are arising much interest.Sodium humate?Na₂HA?with non-conjugated structures is a good candidate for sodium storage applications.Na₂HA is available in abundance in nature,renewable,insoluble in electrolytes,and low-cost.Besides,Na₂HA functionalized by reduced graphene oxide?rGO?has much better electronic conductivity than that of Na₂HA.As anode materials for SIBs,Na₂HA/rGO has a stable discharge specific capacity of 176 m Ah/g at a current density of 100 m A/g,and capacity retention of Na₂HA/rGO electrodes is as high as 92% after 2000 cycles at a current density of 500 m A/g.Na₂HA/rGO electrodes show wonderful high-rate cycling stability.Moreover,ex-situ FT-IR and X-ray photoelectron spectroscopy?XPS?tests initially reveal the mechanism of sodium-storage of Na₂HA,and density functional theoty?DFT?calculations further prove reversible sodium-storage of Na₂HA.3.Disodium rhodizponate?Na₂C₆O₆?has four carbonyl groups on six-carbon ring,which has great potential to be organic electrode materials with high capacity.Similarly,Na₂C₆O₆ has dissolution and poor conductivity problems as organic electrode materials,and this paper focuses on solving these problems.It is first time to prepare copper rhodizonate?CPR?complexes to solve dissolution problems of Na₂C₆O₆,and in-situ assembly of CPR complexes on rGO could dramatically improve the electroconductivity of CPR.Owing to electrostatic interaction among rhodizonate(C₆O₆^2-),GO,and copper ions(Cu²⁺),the CPR/rGO is prepared successfully through a one-pot hydrothermal method.As electrode materials for LIBs,CPR/rGO has a discharge specific capacity of 937 m Ah/g after 100 cycles at a current density of 100 m A/g,a discharge specific capacity of 503 m Ah/g at a current density of 5000 m A/g,and a stable discharge specific capacity of 510 m Ah/g after 250 cycles at a current density of 100 m A/g.CPR/rGO exhibits high capacity and excellent rate capability.4.In our work,an ionic liquid was selected as electrolyte to alleviate the dissolution problem of chloranil electrode materials.The electrochemical activity is improved by reducing the size of chloranil molecules.Three dimentional conductive network is builded to achieve organic electrodes with high loading of active materials.As cathode materials for LIBs,thick electrodes of chloranil show a stable discharge specific capacity of 60 m Ah/g after 50 cycles at a current density of 100 m A/g,and electrochemical performances are enhanced evidently compared with those with tradition electrolyte.The strategy is universal and inspire us to obtain better small organic carbonyl electrode materials.5.The electrochemical performances of chloranil could also be improved through chemical modification.Typically,a sulfurization-based oligomer is prepared successfully by a solvothermal process,and the polymerization degree with sulfur bonds is tunable by controlling the quantity of Na2 S.Besides,the relationship between the polymerization degree with sulfur bonds and electrochemical performances of oligomers was systematacially explored.To improve the electronic conductivity,in-situ growth of oligomers on rGO was carried out by a solvothermal process.Ex-situ dissolution experiments demonstrate the insolubility of composite electrode materials in the organic electrolyte.The as-obtained composite electrode of PDBS/rGO delivers a discharge specific capacity of 165 m Ah/g after 300 cycles at a current density of 100 m A/g,69 m Ah/g at a current density of 5000 m A/g,and 102 m Ah/g after 4000 cycles at a current density of 1000 m A/g.The strategy is of great significance to prepare organic composite electrodes made of small organic carbonyl electrode materials with high-rate properties.