| Compared with other types of lithium ion battery cathode material,olivine-type LiMnPO4 has the advantages of stable lattice structure,high theoretical specific capacity(171 mAh/g),excellent safety performance,abundant raw material and environmental friendliness,etc.It is commonly considered as the next generation cathode materials for lithium ion battery.However,the low electronic and ionic conductivity constrains its further development.Therefore,the key point to achieve excellent electrochemical performance is to increase the conductivity of LiMnPO4.Based on the study with LiMnPO4,a series of research work has been carried out.In detail,based on the two aspects of fabrication and modification,this paper focuses on the key problems affecting LiMnPO4 as a power battery for lithium ion battery cathode material:complex preparation process,low electronic and ion conductivity.Manganese-based precursors have been prepared by the hydrothermal method.The influence of the manganese sources,hydrothermal temperatures,reactant concentration and hydrothermal time on the morphology and phase are investigated.The manganese-based precursor prepared by the hydrothermal method acts as the manganese source,and LiMnPO4 is prepared using solid state sintered technology.The optimum technique parameters are obtained:the hydrothermal time is 14 h,the concentration of manganese acetate is 1 mol/L,and the thermal temperature is 180? with n(Mn3O4):n(C12H22O11)=1:0.75.The optimized LiMnPO4/C has the dispersive particle distribution and uniform carbon coating,which improves the electrochemical performance.Likewise,the multi-layered LiMnPO4/C microspheres are prepared by freeze-drying and high-temperature calcination route with the spherical MnCO3 synthesized by hydrothermal.The multi-level layered structure has the characteristics of three-dimensional carbon network,large specific surface area,and fast ion and electron transport.For the first time,LiMnPO4 has been prepared by electrodeposition through the three-electrode system using the imidazole ionic liquid 1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide(BMIMTFSI)as the electrolyte.The nanorod-like LiMnPO4 is deposited on the surface of platinum mesh electrode Pt/Li3PO4 under the electrolyte temperature of 160? and reduction potential of-0.81 V,which provides a new method for the preparation of LiMnPO4.The effects of different kinds of ionic liquids,ratio of ionic liquids to deionized water on the phase,morphology and electrochemical properties of the products have been investigated systematically.When the imidazole-based ionic liquid is used as a reaction medium for ionic thermal synthesis,pure phase LiMnPO4 is not synthesized.However,when it is used as a template,the pure LiMnPO4 is synthesized except for the ionic liquid containing F-.When the volume ratio of deep eutectic ionic liquids choline chloride/ethylene glycol to deionized water is 1:1,the synthesized LiMnPO4 has the best crystallinity.The composite exhibits the specific discharge capacity of 147.6 mAh/g at 0.05 C(1 C=171 mAh/g),and the capacity retention rate is 99.86%after 20 cycles.Nanorod-like LiMnPO4/C with hierarchical structure has been prepared by anodic aluminum oxide(AAO)template assisted method.The interactive LiMnPO4/C nanorods shorten the transport distance of ions and electrons.When the composite is used as the electrode material,the capacity retention rate is 98.2%and 97.5%after 9 cycles at the current rate of 0.2 C and 1 C,respectively,showing the excellent cycling stability.Likewise,3D-LiMnPO4/C porous nanosheets with honeycomb structure have been successfully prepared by NaCl template assisted method.The mechanical stress caused by the volume change could be alleviated because of the unique honeycomb structure.The electrode material can deliver the discharge capacity of 103 mAh/g at 10 C and the capacity retention rate was 96%after 200 cycles,showing the excellent structural integrity during the long cycle.The composite structure of three-dimensional LiAlO2-LiMnPO4/C has been designed and synthesized using fast ion conductor LiAlO2 as template,which solved the problem of the low conductivity of LiMnPO4.The introduction of LiAlO2 forms a fast channel of Li+,which significantly reduces the polarization of the material,increases the diffusion coefficient,and achieves excellent kinetic performance.The specific initial discharge capacity of the LiAlO2-LiMnPO4/C electrode is 156.4 mAh/g at.05 C,and the discharge capacity retains 105 mAh/g after 100 cycles at 10 C with the capacity retention of 98.4%.Through material architecture design,the unique synthetic method may provide a simple and effective solution for improving the dynamic properties of materials. |
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