Preparation And Properties Of Li-rich Layered Oxides As Cathode Materials

In recent years, due to the global warming and shortage of fossil fuel, the people's living environment was further deterioration, ectricvehicles?EVs? and hybrid electric vehicles?HEVs? appear more viable and necessary than ever before, To meet the requirements, it is necessary to develop new cathode materials with large capacity and better safety. Among the main cathode materials which are commercial such as Li CoO₂, Li Mn2O4 and Li Fe PO4 of LIB. Lithium-rich layered solid solution oxide composites represented by a chemical formula of x Li2 Mn O3·?1-x? Li MO2?M= Mn,Ni and Co? are considered to be one of the most promising cathode materials for high performance lithiumion batteries?LIBs?, because they can deliver an exceptionally high capacity of above 250 m Ah/g and environment friendly. However, the materials are still suffering from several fatal limitations such as a high first-cycle irreversible capacity and a relatively poor rate capability. So this dissertation is intends improve the performance through optimizing synthesis method, dopping modification, coating modification, etc. for performance optimization.First, The lithium-rich layered cathode material Li?Li0.2Co0.13Ni0.13Mn0.54?O2 was synthesized through a facile organic co-precipitation route. The materials were characterized by XRD, SEM, C&D, etc. It is proved that the lithium-rich materials by the organic co-precipitation method have layered crystal structure as ?-Na FeO₂, well-ordered structure without impurity peaks. And optimized the organic co-precipitation method, explored the effect on the crystal structure and electrochemical properties of the material by change the lithium source added and the addition amount of lithium source, wherein the Li OH as lithium source,the added amount was 5%, the electrochemical properties of the material is the best, around 230 m Ah/g at a low rate, can also be reached 160 m Ah/g when current density was 500 m A/g, and later through the template?PVP, SDBS? assisted organic coprecipitation synthesis lithium-rich layered cathode material Li?Li0.2Co0.13Ni0.13Mn0.54?O2, All the peaks in XRD patterns are are subjected to the typical peaks of a rdered rock salt structure??-Na FeO₂? of space group R3 m, when selecting the template poly vinylpyrrolidone?PVP?, 4wt%, the discharge capacity still remains 236.9m Ah/g at a current density of 15 m A/g. Dodecylbenzenesulfonate?SDBS? was elected as a template, 4wt%, the material first discharge capacity increased to 225 m Ah/g, improved rate rate capability, battery still has 198 m Ah/g capacity at a lower rate of 0.5C.Firstly, synthesis lithium rich layered cathode materials and doped F- by organic co-precipitation method,used XRD, The doping scheme optimization were discussed based on the comprehensive characterization including XRD, SEM, C&D, cyclic voltammetry?CV? and AC impedance?EIS?. the first coulomb efficiency would be enhanced and the battery maintains 245 m Ah/g under a current density of 15 m A / g higher than the capacity of any material processed through. V doping lithium rich layered cathode material Li1.2Mn0.54-xNi0.13Co0.13VxO2 would be improved the rate capability, the first discharge capacity was 260 m Ah/g when the doping amount of x = 0.03, and remains 190 m Ah/g at a high rate of 125 m A/g. Cr-doped Li1.2Ni0.13-xCo0.13-yMn0.54-zCrx+y+zO2 cathode material by XRD analysis proved that all materials are attributed to the layered structure of ?-Na FeO₂, we discussed the doping and doping amount for the impact of electrochemical performance under low magnification, only when the chromium doped manganese bit, doping amount is 0.02, the discharge capacity has improved up to 248 m Ah/g, Ce-doped Li1.2Mn0.54-xNi0.13Co0.13CexO2, when doping amount is 0.01, the battery initial discharge capacity is 226 m Ah/g, higher than the 37 m Ah/g of untreated material, at a current density of 500 m A/g, Ce-doped material capacity and the doping amount is 0.03,exceeds the untreated material reached 30 m Ah/g. AC impedance spectra interfacial resistance and charge transfer resistance of the display after doping are improved.Respectively SiO₂, conductive polymer polyaniline?PANI?, polythiophene coating materials are chosen to be coated on the particle surface of Li?Li0.2Co0.13Ni0.13Mn0.54?O2, the 0.5wt% SiO₂ coated material present a best electrochemical properties, and XRD show, SiO₂ does not change the crystalline structure of the material, the material present specific discharge capacity of 225 m Ah/g, probably since electrolyte inert oxide shield the malignant interaction between material and electrolyte. Using conducting polymer of polyaniline deposited and coated on the surface,Polymerization of cyclic voltammetry curves showed that the oxidation peak obviously and redox peaks of strong symmetry, reversible.FTIR showed characteristic peaks with polyaniline, although the material in the process of polymerization of H in electrolyte corrosion due to material and capacity compared with the untreated materials have decreased, but after coating the capacity retention rate of some materials three. After the improvement of boron trifluoride ether?BFEE? as the electrolyte adding monomer, by electrochemical polymerization in the deposited material is coated on the surface of the conductive polymer polythiophene, FTIR showed that the coating of existing characteristic peaks of polythiophene, properties of materials is better than the blank rate after coating materials, coating materials can reach 250 m Ah/g the discharge capacity, discharge rate of 15 m A/g than the blank material is higher 50 m A/g than capacity before and after the coating material XRD were found no impurities. The radiation peak shows that the coating layer is amorphous.