Construction And Sodium-storage Performance Of Of Carbon Nanotube-based Anode Composite Materials

Nowadays,the urgent need to improve energy efficiency and the continuous development of a sustainable energy supply system have created a huge demand for efficient and reliable energy conversion systems.Lithium ion batteries(LIBs)have been widely used in mobile electronic devices and new energy vehicles due to their advantages such as high specific capacity,high efficiency,convenience,and long cycle life.However,the limited lithium resources and high costs seriously hinder its larger-scale application.Sodium ion batteries(SIBs),which are rich in resources and low in cost,are expected to be used in high-performance large-scale energy storage systems.Therefore,the development of anode materials with high energy density and long cycle life for sodium ion batteries is an important task for the application of SIBs.New SIBs anode materials such as Ni₃S₂ and Sb suffer from severe volume effect,leading to serious specific capacity attenuation.Based on this,In this paper,carbon nanotubes(CNTs)with excellent electrical conductivity and stable structure were used to construct particular composite structures with active substances,and studies the electrochemical performance and charge-discharge mechanism of sodium storage.CNTs were used to construct a micro-nano secondary structure with Ni₃S₂,and then its sodium storage mechanism was studied.The content of carbon nanotubes has an important effect on the micro-nano structure and electrochemical performance of Ni₃S₂/CNTs.Ni₃S₂/CNTs composites with CNTs content of 3.8%shows a uniform spherical shape,and the CNTs embedded in the microspheres evenly,introducing abundant mesoporous about 3 nm,which can effectively relieve volume expansion and prevent electrolyte from entering the microspheres.Therefore,an improved electrode stability and high initial coulombic efficiency were obtained.Ex-situ XRD proves that the active substance of Ni₃S₂/CNTs electrode material is mainly Ni₃S₂,and the sodium storage is realized based on conversion reaction with good electrochemical reversibility.The stable SEI films on the surface of the microspheres can not only effectively prevent the loss of polysulfide generated when discharge,but also enable the material to have high coulombic efficiency.The overall structural stability of the active material is the key to realize the long cycle life of the Ni₃S₂/CNTs electrode.First,the directional carbon nanotube arrays were activated and acidified to obtain directional carbon nanotube arrays(HPACNTs)with good orientation,an opened cavity,and rich hierarchical pore structure.Then,Sb Cl₃ was filled into the inner cavity of carbon nanotubes by solution impregnation and melt infiltration,and then the composite material of Sb nanoparticles confined in HPACNTs was prepared by hydrothermal reduction.Among them,the stable and elastic tube walls have an excellent confinement effect on the Sb particles in the cavity,forming a stable nano-reaction container.Meanwhile,the directional arrangement and porous carbon nanotubes not only ensure the conductivity of the composite material,but also shorten the transmission distance of electrons and ions,improving the electrochemical reaction kinetics.When used for sodium ion batteries anode,it shows excellent cycle stability with a specific charge capacity of 477 m Ah g^-1 after 250 cycles at a current density of 1 A g^-1,and an average attenuation of only 0.037 m Ah g^-1 per cycle between 250-4500 cycles.This study provides an effective way to improve the cycle life of anode materials for sodium ion batteries.