Fabrication And Study On Lithium/Sodium Storage Performance Of Metal Compound Anode Materials

With the increasing problems of resource shortage,global warming and environmental pollution,the living environment of human beings is in face of great challenge.The exploitation and utilization of renewable and sustainable energy is imminent.During the exploitation of renewable energy,the most important problem is energy storage and transmission.Long life and low cost energy storage system is the key to solve the problem of energy storage.Lithium-ion batteries(LIBs)have become one of the most important chemical power sources for their high energy density,long life,no memory effect and environmental friendly.Recent years,LIBs have been widely used in portable electronic devices,hybrid electric vehicles(HEVs),electric vehicles(EVs)and green grid energy storage.However,the improvement of battery technology can not solve the scarcity and uneven distribution of lithium resources,so the price of lithium resources is rising,which limits the large-scale development of LIBs.Sodium is rich in resources in the earth's crust and low in price,and the chemical and electrochemical properties of sodium are similar with lithium,so the development of LIBs undoubtedly builds a solid foundation for sodium-ion batteries(SIBs).However,since the radius of sodium ion is much larger than that of lithium ion,the mechanism of sodium ion intercalation and storage in batteries is worthy of further study and exploration.The development and performance optimization of anode materials are crucial for lithium/sodium ion batteries.Among them,metal compounds attract widely attention for the advantage of high specific capacity.However,due to the large volume effect of SnSb,the irreversible capacity is high and the cycle stability is poor.Besides,the cycle and rate performance of metal sulfides are unsatisfactory for their low conductivity and drastic structure change during electrochemical process.Based on above situation,the research emphasis of our work is improving the electrochemical performance of the above metal compounds through specific electrode structure design and battery technology optimization.The main contents are summarized as follows:(1)Through secondary high energy ball milling technology,the in-situ reaction was induced and high performance SnSb/TiO2/C nano-composite with special composite structure was constructed,then the nano-composite was used as anode material of LIBs.In this work,we want to build a nano-composite of SnSb and oxide with multi-level nano-structured,in which TiO2 is the matrix material and SnSb grows on the surface of TiO2 by high-energy ball milling,then the composite was coated with high conductive graphite.By comparing with SnSb/TiO2 and SnSb/C,it can be seen that carbon-coated SnSb/TiO2/C has higher reversible capacity of 630 mA h g-1 and better cycle performance(capacity retention of 80%after 200 cycles).The composite material obtained by in-situ reaction could reduce the effect of volume expansion,relieve the pulverization and peeling of the active material during the electrochemical process,and improve the cycle stability of the electrode material.(2)By high energy ball milling,a series of SnS2-C nanocomposites(SnS2/C-40,SnS2/C-50 and SnS2/C-60)were synthesized and applied in LIBs.The SnS2-C nanocomposites have advantages of high capacity,good cycle stability,high coulombic efficiency and excellent rate performance due to the carbon-coated and nanocrystallization caused by ball milling.When used as anode materials of LIBs,SnS2/C-50 exhibits a high discharge capacity of 863 mA h g-1 at 100 mA g-1,then maintain a capacity of 566 mA h g-1 after 100 cycles,so the capacity retention of SnS2/C-50 is 65.6%.Besides,the initial coulombic efficiency of the sample is up to 80.6%.After moderate carbon coating and ball milling nanocrystallization,the charge transfer resistance of SnS2 is obviously reduced,which demonstrating that the structure conductivity of SnS2-C is greatly improved,and the electrochemical activity of lithium storage is also improved.This improvement is more beneficial to the insertion/extraction of lithium ions in the electrode,thus obtaining better cycle and rate performance.(3)Two kinds of MoS2-C nanocomposites with different carbon contents are prepared by high-energy ball milling method.The MOS2-20%C and the MoS2-30%C were all made of MoS2 nanoparticles coated with amorphous carbon.When used as anode for LIBs,MOS2-30%C with 30%carbon content exhibits a better performance,which shows a high discharge capacity of 736 mA h g-1 at 100 mA g-1,and remains at 720 mA h g-1 after 200 cycles.At a current density of 2000 mA g-1,the reversible capacity of MOS2-30%C was maintained at 428 mA h g-1.In addition,the coulombic efficiency of this sample is also high.After carefully compared with the original MoS2,pure ball-milled MoS2 and MOS2-20%C,it can be seen that the electrochemical performance of MOS2-30%C is improved,which may attribute to the synergistic effect of moderate carbon coating and nanocrystallization by high-energy ball milling.(4)A series of flexible NiS2/C nanofibrous film(NiS2/C-03?NiS2/C-05 and NiS2/C-08)were obtained by electrospinning and subsequent high temperature vulcanization process,and successfully applied in SIBs as binder-free anodes.In this work,nanosized NiS2 was added into the carbon fiber network,and the transmission of electrons and ions were enhanced by this special structure,then the electrochemical performance of the sample was optimized.Due to the characteristics of flexible film,NiS2/C films could be used as a binder-free anode for SIBs.Among the samples,NiS2/C-03 exhibited high capacity(717.1 mA h g-1),excellent rate performance(459.9,416.9,377.5,318.7 and 246.1 mA h g-1 at 100,200,500,1000 and 2000 mA g-1),and excellent cycle performance(initial capacity of 717.1 mA h g-1 and 412.6 mAh g-1 after 100 cycles).The above results show that NiS2/C-03 nanofibrous film is an excellent anode for SIBs.