| The development of green new energy puts forward higher requirements on battery materials.Owing to its low cost,high capacity,good cycle performance and environmentally friendly characteristic,natural graphite has become the choice of lithium ion battery anode materials.But graphite anode material has some defects,such as large first charge-discharge irreversible capacity,low coulomb efficiency in high magnification and so on.In this paper,oxidation,coating and doping were used to improve the shortcomings of graphite anode materials.XRD,SEM,the first charge-discharge,cyclic voltammograms and ac impedance test were used to analyze experimental results.In the experiment,concentrated sulfuric acid oxidation and phenolic resin coate d are used to improve natural graphite morphology defects and enhance the elect ric properties of materials.The effect of different coating amount,calcination tem perature and calcination time on materials properties are discussed.Materials are t ested in voltage of 0.005 V to 0.005 V,ratio of 0.1C,0.2C,0.5C and 1C.The ana lysis shows that performance of natural graphite become better after oxidation.O n the basis of the oxidation,13% amount of cladding,800? calcination tempret ure and 7h calcination time are the best modifying condition for materials.After oxidation,the surface of natural graphite is smooth,particles are arranged orderly and crystallinity is imoroved.The first charge and discharge amount are 319 m A h·g-1 and 333mAh·g-1 in 0.1C ratio,the first coulomb efficiency is as high as 95.7%,it is increased by 3.4% to natural graphite.The first charge and discharge qu antity of optimized cladding material in 0.1C,0.2C,0.5C,1C are 398mAh·g-1 an d 421mAh·g-1,364mAh·g-1 and 388 m Ah·g-1,323mAh·g-1 and 358 m Ah·g-1,221 mA h·g-1 and 251mAh·g-1 respectively.Capacity are 406 m Ah·g-1,364mAh·g-1,320 m A h·g-1and 206mAh·g-1 after 20 cycles respectively.The charge and discharge volume efficiency in 20 cycle are 92.01%,89.02%,86.24% and 75.58% respectively.Doping modification is used to prepare tin-graphite composite material.The effect of different oxide graphite,different doping amount and different calcination onmaterial are discussed.By the analysis of test results,the effect of sulfuric acid oxidation is better than hydrogen peroxide and concentrated nitric acid.1:6 molar mass ratio in SnCl2 and graphite oxide,500? calcination temperature are the best condition.Doping with concentrated sulfuric acid oxidation materials have good crystal structure and surface morphology,the impedance is small,cycle performance is improved.The first discharge in 0.1C ratio is 859mAh·g-1.Relative to HNO3 and H2O2 oxidation material increased 113mAh·g-1 and 76mAh·g-1 respectively.The first discharge capacity in 0.2C,0.5C,1C ratio are 809mAh·g-1,761mAh·g-1,627mAh·g-1 respectively.The first discharge capacity of optimizing materials in 0.1C,0.2 C,0.5C,1C ratio are 1206mAh·g-1,1126mAh·g-1,988mAh·g-1,602mAh·g-1.Discharge capacity after 20 cycles are953mAh·g-1,885mAh·g-1,749mAh·g-1,451mAh·g-1. |
PDF Full Text Request