Design Of CoS₂ Based Anode Materials And Their Sodium Storage Performance

Lithium-ion batteries have been widely used in our life,but the development of lithium-ion batteries is limited by the low reserves and high price of lithium resources.Due to the abundant reserves and low price of sodium resources,sodium ion battery is considered to be an energy storage device which can replace lithium ion battery.Because the graphite anode in lithium-ion batteries is not ideal for sodium ion batteries,it is very important and urgent to find high performance anode materials.Metal sulfides with high specific capacity can be used as anode materials for sodium ion batteries.CoS₂ is considered to be a potential anode material due to its high theoretical specific capacity of 872 mAh g^-1.However,the low conductivity and serious volume expansion of CoS₂ lead to poor sodium storage performance.In view of the above problems,this paper aims to design CoS₂ based anode materials with high sodium storage performance.The specific research is as follows:1. The CoS₂ nanoparticles protected by graphitized carbon?GC?and bamboo-like carbon nanotubes?B-CNT?were designed?CoS₂@GC@B-CNT?.Because of high conductivity and good mechanical stability,graphitized carbon can not only improve the conductivity of materials,but also prevent particle agglomeration.The internal voids of bamboo-like carbon nanotubes can alleviate the volume expansion,stabilize the particle structure,and form a conductive network to provide transport channels for electrons and ions.CoS₂@GC@B-CNT shows good sodium storage performance.At the current density of 10 A g^-1,the capacity is as high as 419.6 mAh g^-1.At the current density of 5 A g^-1,the capacity is maintained at 432.6mAh g^-1 after 900 cycles,and the capacity retention is 95.9%.2. Bimetallic sulfide CoS₂/NiS₂ nanoparticles embedded with carbon nanotubes were designed by introducing NiS₂?CoS₂/NiS₂@B-CNT?.Because NiS₂ and CoS₂have similar structure,they can form a high quality interface and accelerate the transmission of electrons.At the same time,the introduction of NiS₂ enriches the redox reaction and improves the electrochemical performance.Carbon nanotubes can improve conductivity,prevent agglomeration of particles,inhibit volume expansion,and provide electron and ion transport channels.Under synergistic effect of CoS₂,NiS₂ and carbon nanotubes,CoS₂/NiS₂@B-CNT shows excellent sodium storage performance.At the current density of 10 A g^-1,the capacity is as high as 491.6 mAh g^-1.At the current density of 5 A g^-1,the capacity is maintained at 497.6 mAh g^-1 and the capacity retention is 93.0%after 1000 cycles3. The CoS₂ nanoparticles embedded by freestanding and flexible N,S co-doped carbon nanofibers?CoS₂@NSCNF?were designed by electrospinning.Embedding CoS₂ nanoparticles in carbon nanofibers can not only inhibit the volume expansion of CoS₂,but also prevent the agglomeration of CoS₂.At the same time,carbon nanofibers constitute a three-dimensional conductive network,which can improve the conductivity of materials.Nitrogen and sulfur can introduce more defects and active sites and enhance the electrochemical activity.The freestanding and flexible material can be directly used as the anode materials of sodium ion battery.At the current density of 10 A g^-1,the capacity can reach 405.9 mAh g^-1.At the current density of 5A g^-1,the capacity can be maintained at 431.8 mAh g^-1 after 500 cycles.4. The CoS₂ nanoparticles embedded by freestanding and flexible reduced graphene oxide/carbon nanofibers?CoS₂@rGO-CNF?were designed by introducing rGO.The addition of reduced graphene oxide can further improve the conductivity of the material,inhibit the volume expansion of CoS₂ and stabilize the structure.Meanwhile,carbon nanofibers provide transport channels for electrons and ions.The freestanding and flexible materials can be directly used as the anode materials of sodium ion battery.Under synergistic effect of reduced graphene oxide and carbon nanofibers,CoS₂@rGO-CNF shows excellent sodium storage performance.At the current density of 10 A g^-1,the capacity is up to 503.3 mAh g^-1.At the current density of 5 A g^-1,the capacity is kept at 550.5 mAh g^-1 after 300 cycles.