Porous Carbon And Ni-NiO/C Derived From Electroreduction Of Molten Carbonates And Their Electrochemical Properties

Carbon materials with high specific surface area,stable physicochemical properties and low synthesis cost are required to be sodium ion batteries?SIBs?or lithium ion batteries?LIBs?anode candidates.At present,common carbon anode materials include graphite,carbon nanotubes,graphene,and porous carbon.Graphite has a low specific surface area and cannot exhibit a higher capacity.The specific capacity of carbon nanotubes is limited due to the insufficient utilization of inner surface area.Individual graphene suffers from complicated fabrication proces and serious agglomeration.As a high value-added carbonaceous product,porous carbon not only has great applications in SIBs and LIBs,but also plays an important role in the fields of separation,adsorption,catalysis and hydrogen storage.There are many ways to prepare porous materials,but from the view of long-term development,it is extremely important to develop a new method with simple process and abundant raw materials.In this research,the porous carbon was prepared by electroreduction of molten carbonates,and the influence of the molten salt temperature on the porous carbon morphology and the performance of sodium ion batterywas investigated.On this basis,the introduction of transition metal oxide significantly improves the capacity of lithium ion batteries.The main contents and results are as follows:1?In chapter three,porous carbon materials were prepared by electroreduction of molten carbonates?Li₂CO₃,Na₂CO₃,K₂CO₃?.XRD,BET and SEM analysis show that the temperature of molten salts has a great influence on the specific surface area and morphology of porous carbon.Among them,the tremella-like porous carbon prepared at 500 ^oC showed a micro/meso/macroporous hierarchical structure and a high specific surface area(691.77 m² g^-1).This unique structure has the following advantages as the anode of SIBs.On the one hand,micro/mesopore can shorten the ions transport distance,and macropore can provide the sodium ions storage site.On the other hand,the large specific surface area can increase the interface reaction area and improve the amount of sodium ions adsorption.Therefore,the tremella-like porous carbon exhibits high reversible sodium storage capacity:240 m Ah g^-1 at 0.05A g^-1 over 100 cycles.When the current density increases to 5.0 A g^-1,tremella-like porous carbon retained high capacity of 108 m Ah g^-1 even after 1000 cycles.Detailed theoretical calculations show that the high sodium storage capacity of tremella-like porous carbon greatly benefits from non-Faradaic capacitive sodium storage behavior.2?Based on the third chapter,we demonstrate a facile electrolytic strategy to synthesize a kind of Ni-Ni O/C nanocomposite via electroreduction of molten Li-Na-K carbonates synchronously combined with sacrificial nickel anode.Benefiting from its unique in situ synthesis mechanism,the Ni-Ni O/C nanocomposite exhibits well-interconnected architecture with fine Ni-Ni O nanoparticles embedded into electrolytic carbon matrix.The as-fabricated electrode shows ultra-long cycle stability(achieving a high capacity of 455 m Ah g^-1 at 1 A g^-1 after 1500 cycles,average coulombic efficiency 99.88%)and impressively improved rate capability,comparing with the reported Ni-Ni O/C nanocomposites.Such a superior lithium storage properties originates from the in situ formed nanoarchitecture of Ni-Ni O/C.This research offers a distinctive pathway for constructing novel composite materials for advanced lithium storage.