Research On Olivine Type Cathode Materials Preparation Technology And Battery Characteristics For Li-ion Batteries

Among all of cathode materials for lithium ion batteries, the olivine cathodematerials are expected to be applied in electrical vehicle due to its low cost, friendlyenvironment, excellent cycling performance and thermal stability. However, thesynthesized technology and cost for the industrial LiFePO₄are still need to beimproved. In addition, the novel olivine LiMnxFe1-xPO4cathode materials have beenrecognized the promising candidate due to its higher energy density compared witholivine LiFePO₄.In this research, we prepared the olivine-type LiFePO₄and LiMnxFe1-xPO4cathode materials, explored the effects of different preparation approaches on theirmaterials structure, microscopic morphology and electrochemical property. Bysimplifying the process for the practical application, reducing the cost of rawmaterials, coating modification, the electrochemical properties of such materials andthe problem of the Mn dissolution into the electrolyte had been improved. The maininnovations are summarized sequentially as follow:1. LiFePO₄/C composite cathode materials were synthesized by the spray-dryingmethod. By adjusting the composition of the raw materials in the production whilereducing the cost of raw materials, the whole preparation process was moreenvironmentally friendly and safety. The process parameters have been optimizing toachieve fast drying and control of material morphology and particle size. The tapdensity of spherical particles LiFePO₄/C can be achieved1.39g·cm3. Under theoptimized conditions of650oC and10h, the obtained multicomponent olivinecathode material exhibited superior electrochemical performance, delivering adischarge capacity of158.9mAh·g1at0.1C and showed good cycling ability with anegligible capacity fade of200cycles.2. A multicomponent olivine cathode material, LiMnxFe1-xPO4, was synthesisedvia two different methods: solid state method and coprecipitation method. Thesynthesized LiMn_0.4Fe_0.6PO₄/C and LiMn_0.7Fe_0.3PO₄/C exhibit high energy densitiesof557.17Wh·kg1and618.94Wh·kg1. The process parameters of co-precipitationexperiments of pH, reaction time, reaction temperature, aging temperature and otherfactors on the preparation of material particle size and morphology were studied. Andby TG-DTA, XRD, SEM-EDS, TEM, ICP characterization and electrochemical performance analysis, the distribution of each transition metal and theirelectrochemical property were explored. Hence, the electrochemical activity of eachtransition metal in the olivine synthesis via coprecipitation method was enhancedremarkably. We also found that the presence of this kind of material problems andproposed a reasonable explanation.3. The carbon-coated LiMn_0.8Fe_0.2PO₄was prepared by a vapor depositionmethod and nanotechnology. The LiMn_0.8Fe_0.2PO₄/C cathode material exhibitedimproved cycle performance and rate capability, and presented the uniformly particleswith a narrow particle size distribution through the gasoline and ethanol as twodifferent organic carbon. These improved properties were ascribed to a uniformcoating of the nanoparticles, leading to a significant reduction in Mn dissolution intothe electrolyte.