A₄C₈H₂O₆（A=Li/Na） And Biphenyl Quinones Carbonyl Compounds:Synthesis And Application For Li-/Na-ion Batteries

Traditional electrode materials of lithium ion batteries (LIBs) and sodium ion batteries (SIBs) are mostly based on expensive and depletable inorganic transition metal compounds. Recently, the new concept of "green organic rechargeable batteries" promoted the use of the environment friendly, sustainable, and electrochemically active organic compounds as electrode materials of LIBs and SIBs. Organic conjugated compounds have advantages including structural diversity, molecule level controllability, resources renewability, and high theoretical specific capacity. This thesis focus on the designation, preparation and performance study of new type electrode mateirals based on organic small-molecule conjugated compounds. Main contents and results are listed below:(1) Organic tetralithium salts of2,5-dihydroxyterephthalic acid (L14C8H2O6, U4DHTPA) with the morphologies of bulk, nanoparticles, and nanosheets were synthesized through a simple acid-base neutralization reaction, ball-milling and in-situ ultrasonic exfoliation processing, respectively. Electrochemical investigations indicated their applicability as the positive and negative active materials of LIBs. The performance from high to low followed the sequence of nanosheets> nanoparticles> bulk. Remarkably, Li4C8H2O6nanosheets as the positive and negative electrodes showed the discharge capacities of223and241mAh g-1with average voltages of2.6V and0.8V at0.1C rate, respectively. Capacity retentions of94%and96%were sustained after50cycles. Moreover, the use of Li4C8H2O6nanosheets as the initial active materials for both electrodes produced all-organic LIBs with an average voltage of1.8V and an energy density of about130Wh kg-1. The combination of ex-situ IR, in-situ Raman and DFT modeling investigations revealed that reversible redox electrochemical reactions of two two-electron in Na4C8H2O6are separately associated with the enolate groups and carboxylate groups at high potential range of1.6-2.8V and low potential range of0.1-1.8V.(2) Tetrasodium salt NaC8H2O6microrods were synthesized for the first time with2,5-dihydroxyterephthalic acid and sodium hydroxide as raw materials. The microrods had a length of several micrometers and a width of tens to hundreds nanometers. It was demonstrated that reversible two Na+reactions of Na4C8H2O6proceeds smoothly at high potential of2.3V and low potential of0.3V, respectively. The corresponding initial discharge capaicities were183mAh g-1and207mAh g-1with the capacity retentions of84%and89%in the high and low potential region, respectively. The discharge specific capacities at5C were84mAh g-1and117mAh g-1,exhibiting excellent rate capability. The use of "Na-reservoir" Na4C8H2O6as the initial active materials for both electrodes provided the first example of all-organic "rocking-chair" SIBs with an average operation voltage of1.8V and a practical energy density of about65Wh kg-1. Ex-situ IR study and theoretical calculation simulation showed that the active sites at high potential interval of1.6-2.8V and low potential range of0.1-1.8V are the enolate and carboxylate groups of Na48H2O6, respectively. Further quantitative ICP analysis suggested a "shuttle" operation mechanism of the full organic cell.(3) Three kinds of tetra-carbonyl biphenyl quinone derivatives DBT (C14H10O4), BNT (C20H10O4) and BFT (C16H6O6) with similar structure were synthesized by facile oxidative coupling reaction. These compounds were used as the cathode material of LIBs for electrochemical investigations and theoretical calculations. Both experimental and computational results indicated that all the three compounds afford four-electron redox reaction along with4Na+ions intercalation and deintercalation. The initial discharge capacities of DBT, BNT and BFT were406mAh g-1,317mAh g-1, and326mAh g-1,while the utilization efficiency of carbonyl active sites were92%,87%, and96%, respectively. After20cycles, the retained capacities were227mAh g-1,216mAh g-1and170mAh g-1, respectively. These electrochemical results further verified our proposed theoretical rule that the symmetry and distribution of the plots of HOMO electron cloud within the molecular framework can be applied to estimate the utilization efficiency of the active sites of organic conjugated carbonyl compounds.