Polyvinyl Alcohol-assisted Synthesis Of Transition Metal Cathode Materials For Lithium Batteries

At present,because the electrode materials synthesized by transition metal oxides have remarkable advantages in capacity,cost and other aspects,and they are very suitable for use in business models,this kind of electrode materials has attracted extensive attention of researchers and business people.However,it is found that the transition metal oxide electrode materials have some drawbacks.For example,in the process of battery charging and discharging test,the cell volume of the positive material will change significantly,which will affect the specific surface area of the contact material with the battery components,and then change the battery capacity.In addition,the internal resistance of the battery will also change significantly,which will lead to a significant change.The battery changes during the rate performance test.Generally,researchers solve the above mention defects by means of element doping,morphology construction and material coating.Transition metal oxide LiNi_1/3Co_1/3Mn_1/3O₂ electrode material has attracted much attention of researchers because of its high reversible capacity,stable structure,strong thermal stability and low cost.However,researchers have found that the cyclic stability of transition metal oxide electrode materials will weaken obviously after repeated charge-discharge cycles.In addition,the low diffusion rate of lithium ion in this material is also the main reason that hinders its development.In view of these two problems,we have carried out special experimental research.In this paper,we divide the experimental research into two parts.In the first part,we will study the changes of electrochemical properties of electrode materials under the condition of iron doping.Here we use a certain amount of iron to replace nickel in LiNi_1/3Co_1/3Mn_1/3O₂ and then synthesize the required electrode materials.Firstly,the optimum proportion of iron doping is determined,and then the second part of the study is prepared.In the second part,we improved the synthesis of electrode materials by adding polyvinyl alcohol?PVA?.In this part,we focused on the effects of different proportions of polyvinyl alcohol on the electrochemical properties of electrode materials.Using MnCO₃ microspheres as a template and replacing nickel with a certain stoichiometric amount of iron,the electrode material LiNi_1/3-xFexCo_1/3Mn_1/3O₂?0.000?x?0.267?with microspherical morphology was successfully synthesized.By analyzing the XRD data,it can be concluded that the synthesized sample belongs to the structure type of layered?-NaFeO₂.The XRD data can be further refined by RIETAN-FP software,and the law can be obtained.When the doping ratio of iron element is x,when less than 0.133,the lattice constant of the synthesized sample material is proportional to the specific capacity;when the doping ratio x of the iron element is greater than 0.133,the two are inversely proportional;when x=0.133,the electric energy of the doped material Chemical properties are generally superior to other doped ratio materials.The ratio of x=0.133 was selected for the next experimental study.The nine sample materials Li_1.25Ni_0.2Co_0.333Fe_0.133Mn_0.333O₂?PVA=0.0,2.5?were synthesized by polyvinyl alcohol?PVA?sol-gel method,?PVA=0.0,2.5,5.0,7.5,9.0,10.0,11.0,12.5 and 15.0 wt%?.X-ray diffraction,electron microscopy and specific capacity tests were performed on these nine materials.It was proved that the synthetic material had the best electrochemical performance when PVA=10wt%,and the specific capacity retention rate could reach87.7%.