Study On MoS₂ Based Composite Anode Materials For Lithium/Sodium-ion Batteries

Lithium-ion batteries?LIBs?have been widely used in human life for portable electronic devices and electric vehicles because of their cycle stability,high energy density and environmental friendliness.However,with the development of advanced electronic equipments and large-scale transportation systems,the current commercial LIBs should not be able to meet the requirements of energy storage devices due to the limited capacity of electrodes.Meanwhile,the rising costs and limited natural reserves of lithium will further restrict their application,especially in large-scale energy systems.Therefore,developing high-performance LIBs and novel battery systems are extremely urgent.Sodium-ion batteries?SIBs?have been considered as a promising alternative to LIBs in large-scale storage field in view of the wide abundance and low cost of sodium.The electrochemical performances of LIBs and SIBs are mainly decided by electrode materials.Thus,a great deal of effort has been devoted to seeking novel electrode materials with high capacity,excellent rate ability and long cycle performance.Recently,MoS₂,a representative two-dimensional material,has become a potential anode of LIBs and SIBs due to its high theoretical capacity and low price.However,its poor electrical conductivity and uneasing volume change will result in poor rate capability and rapid capacity fading during cycling process.In this paper,we focused on the synthesis and modification of MoS₂ based materials and evaluated their application as anode materials for LIBs and SIBs.In addition,the pseudocapacitance characteristics of those anode materials were also investiagted.The main contents and results of research are as follows:1.Nitrogen-doped carbon/few-layered MoS₂ nanocomposites?MoS₂/PC?were synthesized via low temperature solvothermal and heat treatment.It was found that the addition of carbon precursor could significantly promote the formation of few-layered MoS₂ and improve the performance of lithium-ion and sodium-ion storage.When used as anode of LIBs,MoS₂/PC could deliver a reversible capacity of 482.6 mAh g^-1 at a high current density of 2000 mA g^-1.When used as anode of SIBs,MoS₂/PC could maintain a reversible capacity of 171 mAh g^-1 at a high current density of 1000 mA g^-1after 600 cycles.The pseudocapacitance analysis showed that a significant pseudocapacitance effect of MoS₂/PC appeared when used as anode of LIBs and SIBs.The pseudocapacitance characteristic of MoS₂/PC was beneficial for its excellent rate performance.2.Nitrogen-doped carbon network/few-layered MoS₂ nanocomposites?MoS₂/CAC?were synthesized via a facile freeze-drying and heat treatment.The as-prepared electrodes demonstrated superior lithium-ion and sodium-ion storage performance.When used as anode of LIBs,MoS₂/CAC could maintain a reversible capacity of 801.5mAh g^-1 at 100 mA g^-1 after 100 cycles.Even at a high current density of 2000 mA g^-1,MoS₂/CAC could deliver a high reversible capacity of 599.8 mAh g^-1.When used as anode of SIBs,MoS₂/CAC could maintain a reversible capacity of 354 mAh g^-1 at 50mA g^-1 after 100 cycles.MoS₂/CAC could also deliver a high reversible capacity of298.7 mAh g^-1 at a high current density of 1000 mA g^-1.The pseudocapacitance analysis also showed that a significant pseudocapacitance effect of MoS₂/CAC appeared when used as anode of LIBs and SIBs.3.Carbon tube/few-layered MoS₂/TiO₂ nanocomposites?CMT?were rationally designed and synthesized.It was found that the TiO₂ coating is vital for the lithium-ion and sodium-ion storage performance.When used as anode of LIBs,CMT could deliver reversible capacities of 528.5 and 455.2 mAh g^-1 at high current densities of 1000 and2000 mA g^-1 after 1000 cycles,respectively.When used as anode of SIBs,CMT could maintain 130.9 mAh g^-1 at a current density of 500 mA g^-1 after 1000 cycles.In addition,the pseudocapacitance analysis showed that a significant pseudocapacitance effect of MoS₂/PC appeared during the charge and discharge process.Especially,the capacitive contribution could reach 85.6%when used as anode of SIBs.The high capacitive contribution can avoid the volume change of electrode structure and improve its rate performance.4.Ti₃C₂T_x/few-layered MoS₂ nanocomposites?FMCT?were synthesized via low temperature solvothermal and heat treatment.When used as anode of LIBs,FMCT could deliver a reversible capacity of 490.7 mAh g^-1 at 100 mA g^-1 after 100 cycles.Especially,FMCT could maintain 403.1 mAh g^-1 even at a high current density of 2000mA g^-1 after 1200 cycles,indicating its excellent cycling stability.However,the rate performance of FMCT still needs to be improved.The pseudocapacitance analysis showed that the lithium-ion storage was dominated by diffusion controlled process.The dominant diffusion controlled process should be the important reason for its low rate performance.When used as anode of SIBs,FMCT could deliver 137.5 mAh g^-1 even at a high current density of 2500 mA g^-1.In addition,FMCT could maintain 135.7 mAh g^-1 at a current density of 1000 mA g^-1 after 1900 cycles with coulombic efficience of nearly 100%.Meanwhile,the pseudocapacitance analysis showed that a significant pseudocapacitance effect of FMCT appeared when used as anode of SIBs.