Preparation And Modification Of Vanadium Pentoxide As Cathode Material For Lithium Ion Batteries

At present,common commercial cathode materials are lithium cobalt oxide（LiCoO2）,lithium manganese oxide（LiMn2O4）and lithium iron phosphate（LiFePO4）,while vanadium oxides such as vanadium pentoxide（V₂O₅）can insert/extract multiple lithium ions and release the higher theoretical capacity has also been widely concerned by the lithium-ion battery（LIB）industry.The unique layered structure in the vanadium pentoxide composed of a pyramid layer composed of VO5 provides a huge space for the insertion/extraction of lithium ions.However,the poor structural stability ofα-V₂O₅ leads to poor cycling stability.In addition,low electronic conductivity,low ion conductivity and slow electrochemical kinetics also limit its performance.In order to solve the above problems,this paper studies the modification of vanadium pentoxide from the two perspectives of construction of micro-nano materials and ion doping,and optimizes its morphology and electrochemical performance.Firstly,this article synthesized V₂O₅ micro-nano-level materials of different dimensions to improve its electrochemical performance.Using commercial V₂O₅ as raw material,through hydrothermal and calcination processes,one-dimensional nanoribbons and two-dimensional micro-flake V₂O₅ materials are obtained;at the same time,in order to obtain a three-dimensional structure,ammonium metavanadate is used as raw material and urea is used as morphology modifier,Using the same process,an octahedral structure is obtained.Tested under a voltage window of 2.5-4.0 V,the V₂O₅ nanoribbons and microflakes showed initial discharge capacities of 169 and 155 m Ah/g respectively at 1 C for the first cycle,and the capacities were 105 and 106 m Ah/g respectively after 200 cycles,corresponding to The capacity retention rate is 86%and 80%;the initial capacity of the V₂O₅ octahedron is 142 m Ah/g,and the discharge specific capacity remains at129 m Ah/g after 250 times,and the retention rate is 91%.It can be seen that the interconnected structures and micro-nano units in low-dimensional materials synergistically improve the electrochemical performance of V₂O₅.On the other hand,the octahedron has better electrochemical performance.This is due to the three-dimensional structure,which can reduce the Li⁺diffusion distance,and the deintercalation of lithium ions becomes more efficient;on the other hand,the three-dimensional structure effectively releases the internal stress during the charge and discharge process,making the electrode material obtains more stable cycle performance.In this paper,the method of ion doping is used to test under a wider voltage window.The fluorinated material can obtain a higher capacity while ensuring the stability of the structure.Using commercial V₂O₅ as a raw material,it is fluorinated by hydrothermal method to obtain fluorinated V₂O₅（V₂O₅-F）.Study the effect of fluoride ion doping on the structure,morphology and electrochemical performance of V₂O₅.The doping of fluorine can affect the growth of grains and adjust the size o f grains formed.As the degree of fluorination increases,the particle size keeps getting smaller,and the morphology tends to be consistent and regular,indicating that doping with fluorine will also affect the growth orientation of the crystal plane.V₂O₅-F maintains good cycle stability at high current density.The initial discharge specific capacity at 5 C is 227 m Ah/g.After 400 cycles,the discharge specific capacity can still be maintained at 167 m Ah/g,and the capacity retention rate is 74%,the material has a high specific capacity and high retention rate when cycling at a large current density under a voltage window of 2.0-4.0 V.The doping of fluoride ions improves the capacity and cycle stability of vanadium pentoxide,making it show higher reversibility during charge and discharge.