Synthesis And Performances Of Novel Layered Lithium Manganese Oxides As Cathode Materials For Li-ion Batteries

To meet the increasing demand of electric vehicles?EVs?,it is efficient and urgent to explore high-capacity cathode materials for lithium ion batteries?LIBs?.In comparison with the commercial LiCoO₂ and LiFePO₄,layered manganese oxide?LiMnO₂?possesses higher operation voltages and capacities in particular,and hence is considered as a promising substitution.However,the low Li⁺/electron conductivity,Jahn-Teller distortion,and the solution of Mn²⁺ions during cycling seriously restrict its large-scale commercial applications.To resolve these shortcomings,researchers mainly focused on three modification strategies.?1?Preparing nanomaterials can shorten the transport path of electrons and Li⁺ions in comparison with the bulk one.?2?Doping with metal ions or preparing xLi₂MnO₃·?1-x?LiMnO₂ composites can optimize the crystal structure for better conductivity and structure stability.?3?Modifing the surface can minimize the direct contact between active particles and electrolytes and resultantly suppress or avoid the dissolution of manganese.In this work,well-dispersed 0.4Li₂MnO₃·0.6LiMnO₂composites were fabricated via a two-step hydrothermal method and further modified by Al₂O₃ and AlF₃ coating.X-ray diffraction?XRD?,scanning electron microscope?SEM?,and transmission electron microscope?TEM?were performed to confirm the composition,structure,and morphology.Galvanostatic charge-discharge,cyclic voltammetry?CV?,and electrochemical impedance spectroscope?EIS?were carried out to systemically analyze the electrochemical performances.?1?The well-dispersed 0.4Li₂MnO₃·0.6LiMnO₂ composites were fabricated by a hydrothermal method.Profiting from the electrochemical pretreatment,the sample showed a⁶%-higher reversible capacity of189.4 mAh g^-1?after 30 cycles?.It suggests that the electrochemical treatment can effectively activate Li₂MnO₃ for more lithium storage capacities..?2?The 0.4Li₂MnO₃·0.6LiMnO₂ composites were further modified Al₂O₃ and AlF₃ coating layers in aqueous solution.The results showed that both Al₂O₃ and AlF₃ uniformly coated the composites.The sample with 5wt%Al F₃ exhibited better cyclic stability and rate capability.The reversible capacity remained 123.1 mAh g^-1 after 50 cycles.In conclusion,well-dispersed 0.4Li₂MnO₃·0.6LiMnO₂ composites were fabricated via a hydrothermal method and further modified by Al₂O₃and AlF₃ coating.When used as cathodes for LIBs,the samples presented considerable cycling performance and high rate capability,in which the electrochemical treatment and coating modification played an important role.