Preparation And Electrochemical Sodium Storage Of Biomass-derived Carbon/Transition Metal Sulfide Composites

Sodium ion batteries(SIBs),as the most promising new generation of energy storage device which has advantages of low cost,high safety and quick charging,have lower capacity and cycle performance than lithium-ion batteries,duing to the larger Na⁺ionic radius and the strongther resistance to intercalate/deintercalate among the electrode material.Therefore,it's great significant to research and development original electrode materials of excellent electrochemical performances for SIBs.MoS₂,as a typical layered metal sulfide,is very suitable for metal ion intercalation/deintercalation.In this thesis,the core-shell structure of carbon based on biomass/MoS₂ composite materials were constructed by hydrothermal method and normal temperature coating,and the electrochemical properties of sodium storage were systematically studied.The main research contents and conclusions are as follows:(1)BC/MoS₂@N-C composites with 3D core-shell structure were constructed by hydrothermal method and polymer-calcination method,during which the bifidobacterium was used of a carbon skeleton(BC).The 3D carbon conductive skeleton was builded by biomass carbon matrix and dopamine-derived carbon coating,which promoted the reaction kinetics of electrochemical sodium storage,mitigated the agglomeration of MoS₂ nanosheets and volume expansion in the process of charge/discharge,so as to obtain excellent electrochemical sodium storage performances.Such as at the current density of 0.2 A/g,after200 cycles,it can still maintain a reversible specific capacity of 371 m Ah/g,and at the large current of 2 A/g,the reversible capacity can also reach 351 m Ah/g.(2)A hollow tubular WC/MoS₂@N-C composite electrode was constructed with the waste water hyacinth stem as the carbon skeleton(WC).MoS₂ nanosheets were uniformly grown on the surface of WC and coated with a layer of nitrogen doped carbon by polymerization.Such hollow core-shell structure makes the electrolyte be in contact with the active material fully,promote the electrochemical reaction kinetics,nitrogen doped carbon coating layer at the same time,building a layer of a physical barrier layer,which can effectively promote the conductivity of the electrode material and structure stability,and thus achieve a good electrochemical storage performance.It can maintain a reversible specific capacity of 328.6 m Ah/g after loop 150 times at 0.1 A/g,and the retention rate is up to 97%.(3)The PC/MoS₂@PPy composite with core-shell structure was constructed with the carbon skeleton of stacked reticular Kapok flower petals(PC)and the outer coating of conductive polymer PPy.Modified by the double carbon conductive network and porous structure,the PC/MoS₂@PPy electrode with extended layer spacing(0.98 nm)showed excellent sodium storage performance.The initial discharge capacity at 0.1 A/g current density is up to 652.9 m Ah/g,and remains 394 m Ah/g after 100 cycles.