Research Of Chalcogenide As Anode Materials Of Lithium-Ion Batteries

Lithium-ion batteries,as a new generation of clean and green secondary battery energy storage systems,have become the first choice of current energy storage systems.At present,commercial lithium-ion batteries generally use graphite as the anode material,but the graphite has low tap density and low specific capacity(372 mAh g-1).As well as low lithium insertion potential,which makes the battery easy to deposit lithium during the cycle and generate lithium dendrite,causing a series of safety hazards.Therefore,graphite anodes have been unable to meet people's needs for high-capacity and high-safe lithium-ion batteries.Based on this,the development and research of anode materials for high-performance and high-safety lithium-ion batteries has become a hotspot for current researchers in lithium-ion batteries.Chalcogenide compounds,especially oxy compounds and chalcogen compounds,have become a new generation of anode materials with commercial potential due to their high theoretical specific capacity,suitable lithium intercalation potential,low price,and environmental friendliness.But at the same time,oxygen compounds are facing some obstacles on the road to commercial development.For example,the metal oxide based on the conversion reaction has low conductivity and large volume expansion affects the coulomb efficiency and cycle stability during the cycle;while the vanadium oxide based on the intercalation/deintercalation mechanism has good cycle stability and smaller volume expansion,but also facing problems such as unknown thermal safety and stability;in addition,metal sulfide has excellent cycle rate performance,which also makes it a potential anode material for development.However,because metal sulfides are not active in ester electrolytes,and ether electrolytes have weak oxidation resistance,and it cannot match high-voltage commercial cathode materials,which limits the development of metal sulfides;This thesis focuses on the problems mentioned above,and carries out research on the modification and mechanism of lithium ion battery anode materials from three directions,including the following:1.CoFe2O4 is used as a representative of conversion mechanism metal oxides to study the modification of materials.In order to solve the problems of low electrical conductivity and volume expansion,a soft template-assisted spray-drying method was used to synthesize a carbon composite material PS-CFO/CNTs/rGO with a honeycomb structure.In this composite,carbon nanotubes serve as the conductive network skeleton,and reduced graphene oxide isolates the direct contact between the material and the electrolyte.The hollow and porous structure provides a good buffer space.The combination of these three effectively improves the overall composite conductivity and mitigates volume effects.Electrochemical tests show that PS-CFO/CNTs/rGO composites exhibit high reversible discharge specific capacity and excellent cycle performance in lithium-ion batteries(at 0.2 A g-1,maintain a high reversible capacity of 916 mAh g-1 after 100 cycles).The mechanisms of electrochemical and reaction kinetics of the composite were studied by Cyclic Voltammetry(CV),Galvanostatic Intermittent Titration Technique(GITT),and electrochemical impedance spectroscopy(EIS).It was found that the complex of carbon and the design of the structure can effectively shorten the lithium ion diffusion path and enhance lithium ion conduction.And through a novel pretreatment method,the pole pieces are pretreated and applied to sodium ion batteries,which improves the reversible capacity and high rate cycling performance of sodium ion batteries(at current density of 1 A g-1,the reversible specific capacity is still maintained at 195 mAh g-1 after 5000 cycles.)This method can be applied to other oxide materials.2.Li3VO4 anode is used as the representative of the intercalation/deintercalation mechanism oxide to investigate the thermal behavior mechanism.The DSC test was used to analyze the thermal behavior mechanism of Li3VO4/Li system.The reaction mechanism of exothermic peaks in different temperature sections of 35-800? was analyzed by controlling variable method.The thermal reaction temperature and exothermic heat of the active material,the passivation film on the surface of the material,the electrolyte and the binder in the Li3VO4 system were analyzed separately.And through the condition experiment,it is found that the heat release of the system increases with the number of cycles and the degree of lithium intercalation,and the degree of lithium intercalation has a greater effect on the heat release.This systematic thermal analysis has guiding significance for the future commercial safety design of Li3VO4 batteries.3.The Cu2S anode is used as the representative of sulfide to study the compatibility with the ester electrolyte.Modified the system of Cu2S and ester electrolyte through carbon-embedded,artificial SEI,electrolyte additives and other methods to improve the cycle performance of Cu2S in the ester electrolyte(Before modified,it will be inactivated after five cycles,and the capacity will decrease to zero.After modification,the reversible specific capacity of 308 mAh g'1 is maintained after 100 cycles at a current density of 0.2 A g-1).The SEI-formation mechanism of the electrolyte additive was investigated,and it was found that the VC electrolyte additive would form a film on the side of the Cu2S electrode,thereby exerting a desolvation effect.