Preparation And Lithium/Sodium Storage Properties Of Sunflower Seed Shell Based Carbon Spheres And Their Composites

With the massive application of clean energy,energy storage technology has been developed into the mainstream direction of research today.Among them,Lithium-ion batteries are widely used in electronic products,electric vehicles and other fields because of their excellent cycle performance,high reversible specific capacity as well as green and pollution-free.In the past decades,although LIBs have been rapidly developed,it still doesn’t meet the needs of people.In addition,the reserve of Li on the earth is limited,and its use cost will increase year by year.Therefore,it is urgent to study its substitutes while developing LIBs batteries.Na is considered to be the most hopeful replacement for Li since it has abundant resources and low cost.It is well known that the most commonly used anode material for LIBs/SIBs is graphite.Due to its low theoretical specific capacity(372/279 m Ah g^-1)and poor multiplier performance,it is difficult to meet the growing demand for energy storage equipment.Therefore,it is extremely essential to seek better anode materials to replace graphite.Because of the high theoretical specific capacity(838/548 m Ah g^-1),transition metal compounds MoO₂ and MoSe₂are particularly suitable to be used as LIBs/SIBs anode materials.However,as a result of huge volume change,slow reaction kinetics and easy agglomeration during charging and discharging,their practical applications are extremely limited.In this paper,sunflower seed shell carbon balls were combined with nano-sized MoO₂ and MoSe₂ respectively by hydrothermal method to prepare electrode materials,and the influence of volume effect on capacity was reduced by nanization.In this work,we first studied the electronic structure of the materials through the calculation of DFT and tested the rationality of the existence of the composite materials SSCC/MoO₂ and SSCHC/MoSe₂.At the same time,it was found that the construction of the composite materials could increase the stability of MoO₂and MoSe₂ and reduce the adsorption energy of Li⁺/Na⁺,so as to realize the irreversible adsorption to reversible absorption.Its electrochemical properties were investigated by a series of characterization and tests.The specific research content is as follows:（1）High-performance LIBs/SIBs anode material SSCC/MoO₂ was prepared by successfully attaching MoO₂ small particles to carbon spheres using the solvothermal method.The core-shell structure formed by nano MoO₂ and SSCC can reduce the capacity attenuation caused by volume expansion during charge and discharge,thus improving the cycle stability.In addition,SSCC and MoO₂ have been shown to be strongly connected via C-O-Mo bond,which provides a good pathway for charge transfer,thus improving the rate performance Thanks to the above characteristics,when SSCC/MoO₂ acts as the negative electrode of LIBs,its capacity finally stabilizes at 1441.3/654.9 m Ah g^-1 after 100/1000 cycles at 0.2/2 C.When used as SIBs anode material,the capacity stabilizes at 345.6 m Ah g^-1 after 180 cycles at 0.2C.（2）MoSe₂ nanosheets were coated on the surface of hollow carbon spheres by solvothermal method to prepare SSCHC/MoSe₂ composites.As the frame material,C material can enhance the electrical conductivity of MoSe₂ and avoid the problems of volume collapse and agglomeration.As a LIBs anode material,SSCHC/MoSe₂ has excellent electrochemical performance,showing excellent capacity retention rate,long cycle stability and good cycle stability.After 150/5500 cycles at 0.2/5 C,the capacity of SSCHC/MoSe₂ as a LIBs anode material finally stabilizes at 1662.5/470.1 m Ah g^-1.When used as SIBs anode material,after200 cycles at 0.2 C,the capacity stabilizes at 320.3 m Ah g^-1.