Synthesis And Properties Of High Conjugated Carbonyl Cathode Materials And Schiff Base Anode Materials For Sodium-ion Batteries

In cathode materials of SIBs, organic conjugated carbonyl compounds have advantages including high theoretical specific capacity and low solubility in electrolytes. In anode materials of SIBs, Schiff base compounds have been gradually used in anode of SIBs due to their low oxidation and reduction voltages. The serious attenuation of specific capacity in small molecule carbonyl and schiff base compounds as electrodes in sodium-ion batteries was resulted from high solubility in electrolyte,however, the effective way to change the high solubility problem is prepare the polymer electrodes and complex with the high conductive carbon material of large specific surface. This paper focus on the designation, synthesis and sodium-storage properties of electrode mateirals based on organic conjugated carbonyl and Schiff base compounds. Main contents and results are listed below:(1) Polymeric carbonyl compound namely polyimide(PI) has been prepared by a facile one-pot polycondensation. The electrochemical performance of the PI as cathode material for SIBs was studied systemically in three electrolyte systems(Na PF6/EC:DMC, Na Cl O4/EC:DMC and Na Cl O4/EC:PC). Study show that the attractive electrochemical properties of PI in Na Cl O4/EC:PC are closely related to the highest ionic conductivity, then, PI have the highest initial specific capacity of110 m Ah g-1and the best rate performance in Na Cl O4/EC:PC. At all current densities, in Na Cl O4/EC:PC, the capacities of PI are higher than other two electrolytes and PI delivers high reversible capacities of 100 and 89 m Ah g-1 at 2C and 8C.(2) Salicylaldehyde-based Schiff base cobalt(?)(SSB(Co)(?)) complexes have been synthesized from salicylic aldehyde, ethylenediamine and cobaltous acetate, SSB(Co)(?) complex/reduced graphene oxide(r GO) composites have been prepared using r GO and SSB(Co)(?) as precursors.Electrochemical experiments show that the superior electrochemical performances of the composite are due to the structure that the SSB(Co)(?) was dispersed in the three dimensional conductive network of r GO, which can improve the electrical conductivity of SSB(Co)(?)and reduce the complex solubility in electrolyte by strengthening the active complex. The SSB(Co)(?)/r GO electrode can deliver a higher discharge capacity(155 m Ah g-1 at 0.2C), greatly improved rate capacity(95 and 76 m Ah g-1 at 1C and 2C) and cycle stability(87.7% capacity retention after 100 cycles at 1C) in comparison with the SSB(Co)(?) electrode.(3) Salicylaldehyde-based polymeric Schiff base compound(SPSB) has been prepared from salicylic aldehyde, ethylenediamine and formaldehyde through two-step method, salicylaldehyde-basedpolymeric Schiff base cobalt(?) complexes(SPSB(Co)(?)) have been synthesized using cobaltous acetate and SPSB. The results show that the SPSB can deliver a reversible discharge capacity of 181 m Ah g-1 at a current density of 0.2C, the capacity remain 103 m Ah g-1 after 100 cycles with 57%capacity retention. At 2C, 4C and 8C, the SPSB also delivers a discharge capacity of 77, 64 and 49 m Ah g-1, respectively. the SPSB(Co)(?) shows higher specific capacities under different current densities, however, poorer cycle stability compared with pure SPSB. At 0.2C, the SPSB(Co)(?)delivers the discharge capacity of 211 m Ah g-1 only with 38.2% capacity retention during first 30 cycles. Also at 2C, 4C and 8C, the complex can deliver the discharge capacity of 118, 95 and 71 m Ah g-1, all higher than pure SPSB.