Synthesis And Surface Modification Of Spinel Lithium Manganese Oxide Cathode Materials

Because of abundant manganese resources,low cost,environmental friendliness etc.,spinel LiMn₂O₄is one of the most promising cathode materials for lithium-ion batteries.However,LiMn₂O₄usually suffers from the poor cycling stability and capacity deterioration during clycling,originating from well-known Mn dissolution,which restricts its industrial application,for instance,electric vehicles?EVs?and hybrid electric vehicles?HEVs?.To address these issues,many strategies have been reported to enhance the electrochemical performances of spinel Li Mn₂O₄.?a?The surface coating is one of effective and controllable approach that can be taken to prevent the contact between LiMn₂O₄ and electrolyte.?b?doping ions of a small fraction at the manganese sites can be investigated to stabilize the electrode material structure.?c?The morphology control can shortentheelectrons and ions transport length.In our work,we reported the synthesis of spinel LiMn₂O₄ via a two-step method in which the special morphology of Mn₃O₄ was easily obtained by the hydrothermal method.Then the truncated octahedral LiMn₂O₄ was prepared from the solid-state lithiation process.The truncated octahedral LiMn₂O₄ cathode materials present superior electrochemical properties.By optimizing the synthesis process of some important parameters,we obtained the lithium manganese oxide cathode material with good rate and cycling performance from the study of commercial lithium manganese oxide by surface coating to prevent the direct contact of electrode material and electrolyte and inhibit the dissolution of manganese,The major reseach contents as follows:?1?The uniform and well shaped Mn₃O₄ nanocrystals were synthesized via a facile one-pot hydrothermal reaction under the help of polyethylene glycol as both reducing reagent and structure-directing agent,potassium permanganate as manganese source,and water as solvent.Then the products were transferred to the truncated octahedral LiMn₂O₄ by solid-state lithiation process.We studied the factors of polymerization degree,reaction temperature,and reaction time on the morphology and structure of Mn₃O₄.We want to explore the growth process and the growth mechanism of Mn₃O₄.From further optimizing the lithium manganese molar ratio,calcination temperature,calcination atmosphere,we studied the effect of the morphology,structure,and composition of lithium manganese oxide.The results indicate that more Mn⁴⁺is formed in the surface and the average valence of Mn was improved under the oxygen atmosphere,which can inhibit effectively the Mn dissolution and promote the chemical stability.The discharge capacities of the lithium manganese oxide cathode materials are 110 mAh·g^-1,110 mAh·g^-1,105 mAh·g^-1,102 mAh·g^-1,99 mAh·g^-1 at 0.1 C,0.2 C,0.5 C,0.8 C,1.0 C,respectively and the capacity retention rate was about 93.9%after 500 cycles at 1.0 C.Here,we obtained the lithium manganese oxide cathode materials with good rate and cycling performance.?2?By controlling the hydrolysis of sodium silicate,a uniform and dense SiO₂ coating layer was coated in the commercialization of lithium manganese oxide material,and the existence of the coating layer can effectively prevent the direct contact of electrode material and electrolyte,further inhibiting the dissolution of manganese on the surface.When the coating amount is 0.5%of SiO₂,the capacity retention rate was about 75%after 300 cycles at 1.0 C.Therefore,we obtained the cathode materials with the best electrochemical performance.In order to reduce the corrosion of HF in the electrolyte and improve the cycle stability,the SiO₂ and Al₂O₃ double components coated LiMn₂O₄ cathode materials?SLMO@SiO₂@Al₂O₃?were designed and prepared.The results indicate that the cycling performance of the electrode material has been further improved under the double coating.