Study On Preparation And Potassium Storage Properties Of The Transition Metal(Ni,Co,Fe) Chalcogenides

Lithium ion batteries are widely used for high energy density.But the lack of lithium resources and uneven distribution lead to its high price.Hence,it is necessary to seek new rechargeable batteries.Potassium,which is located in the same main group with lithium,possess similar chemical properties of lithium.Potassium ion batteries are promising new energy storage system with abundant resources and low cost.Transition metal chalcogenide as anode materials for potassium ion battery possess high theoretical capacity and abundant resources.However,the serious volume expansion and poor electrical conductivity hinder their further development.In addition,the electrolyte directly influences the formation of SEI on the electrode surface,and plays a crucial role in the batteries.This paper aims to improve the electrochemical performance of transition metal chalcogenides as anode materials for potassium ion batteries through the improved strategies,such as structural design of materials,carbon coating and electrolyte optimization.The detailed works included the following parts:?1?Nano-rose-like NiCo₂S₄/C composites were prepared by a simple hydrothermal method.On the one hand,the rose-like structure can provide a large specific surface area(146 m² g^-1),thus ensure sufficient infiltration of electrode materials and electrolyte.On the other hand,carbon coating can improve the conductivity,ease the composites volume expansion and improve the structural stability.In addition,compared with pure NiCo₂S₄ and carbon material,the electrochemical performance of NiCo₂S₄/C composite material is the best.After 650 cycles at the current density of 200 m A g^-1,it has a reversible capacity of 196 m Ah g^-1.At the current density of 1000 m A g^-1,it has a discharge specific capacity of 150 m Ah g^-1,showing a good rate capability.?2?FeSe₂-NC composites were synthesized by a simple solid-phase sintering,FeSe₂-NC composites have a large specific surface area and a special structure that can shorten the transport distance of potassium ions.Compared with 0.8 M KPF₆·EC/DEC electrolyte,the ionic diffusion rate of the electrode in 1 M KFSI·EC/DEC electrolyte is faster,and the SEI formed on the surface is more stable.The constant current charge-discharge test showed that FeSe₂-NC electrode had a reversible capacity of 460 m Ah g^-1 after 100 cycles at 100 m A g^-1,and the discharge capacity remained at 237 m Ah g^-1reversible capacity after 950 cycles at current density of 2000 m A g^-1 without obvious attenuation.Furthermore,the products of FeSe₂-NC during charging and discharging were further analyzed,and the mechanism of its potassium storage was studied.?3?The clubbed Fe₃Se₄/FeSe₂ carbon nanofiber composites were synthesized by electrostatic spinning.The spun Fe₃Se₄/FeSe₂ embedded in carbon nanofibers,which has a small particle size speeds up ion transport.Carbon nanofibers provide a good conducting network as well as relieve the bulk expansion of particles.It also presents a discharge specific capacity of 413.6 m Ah g^-1 after 100 cycles at 100 m A g^-1,and a high reversible capacity of 203.4 m Ah g^-1 at a high current density of 1000 m A g^-1.