Preparation And Electrical Property Research Of Phosphate Cathode Composite Materials And Iron Oxide-based Anode Composite Materials

In this paper,a brief review about the lithium-ion battery was presented firstly.The advantages of the phosphate cathode material and the iron oxide-based anode materials were analyzed,and then puts forward the research emphasis of this paper: the lithium-ion battery electrode material was modified by the material with excellent electrical conductivity,in order to improve the electrochemical properties of the electrodes.The main content of this paper is as follows:?1??-LiVOPO₄ was synthesized by a sol-gel method,and then polyaniline?PANI?was coated on ?-LiVOPO₄ to get the ?-LiVOPO₄/polyaniline??-LiVOPO₄/PANI?composites.Scanning electron microscopy and transmission electron microscopy images show that the ?-LiVOPO₄ material was coated with a layer of polyaniline.Polyaniline presence greatly improves the conductivity of the material,thereby improving the electrochemical properties of the material.The initial discharge capacity for the composite material was 130.9 mAh/g at the current density of 16 mA/g,the discharge capacity was still 125.3 mAh/g after 100 cycles,and the capacity retention rate was 95.7%.?2?Li₃V₂?PO₄?₃?LVP?nanoparticles were first prepared via a simple sol-gel route,then deposited on graphene oxide nanosheets,and finally a composite of LVP/reduced graphene oxide?LVP/G?was obtained after heat treatment.Scanning electron microscope and transmission electron microscope images demonstrate that LVP nanoparticles are homogenously enwrapped into graphene nanosheets or anchored onto the surface of graphene nanosheets.Compared with pure LVP,LVP/G nanocomposites exhibited better electrochemical performance?118.4 mAh/g at the current density of 140 mA/g,and 112.1 mAh/g at the current density of 280 mA/g after 100 cycles?and higher cycling stability?97% capacity retention after 100 cycles at the current density of 140 mA/g,and 89.5% after 500 cycles at the current density of 1800 mA/g?as cathode materials for Li ion batteries.The enhanced performance can be attributed to the presence of graphene nanosheets among LVP nanoparticles.Electrochemical impedance spectroscopy indicates that graphene nanosheets significantly improve the electrical conductivity of LVP.?3?In this work,Li₃V₂?PO₄?₃ co-modified by nitrogen-doped GNSs and carbon coating composites?LVP/NGC?are fabricated for the first time,through a xerogel method using melamine-formaldehyde resin as carbon and nitrogen sources.Transmission electron microscopy and scanning electron microscopy showed that the nitrogen-doped carbon-coated LVP particles uniformly dispersed in the nitrogen-doped graphene surface.The obtained architecture combines two types of electronic contact with Li₃V₂?PO₄?₃ particles: the point-to-face contact of N-doped graphene and the face-to-face contact of N-doped carbon coating layers.Profiting from the favorable complex structure,graphene and carbon coating layers offer an extraordinary network for electron transfer and hence an excellent long-term and high-rate performance.At the current density of 5600 mA/g,the reversible capacity still maintains 86.9 mAh/g after 800 cycles without any fading.?4?Ultra-small Fe₃O₄ nanocrystals?NCs?/graphene nanosheets?GNSs?composites have been synthesized through a facile gel-like film?GF?assisted method in this work.Scanning electron microscope and transmission electron microscope images demonstrate that Fe₃O₄ NCs with particle size ¹0 nm homogeneously dispersed on 2D GNSs.Profiting from the ultra-small Fe₃O₄ NCs and GNSs,the composites demonstrate superior long-term and high-rate performance as anode materials for lithium ion batteries.Even at the current density of 5000 mA/g,the reversible capacity still maintains 323.4 mAh/g after 700 cycles.