Deep Eutectic Solvent Synthesis Of Nanostructural LiMnPO₄/C And Its Use As Cathonde Material For Lithium-ion Battery

Olivine-tpye LiMPO4(M= Fe,Mn)cathode materials have been considered as a promising cathode material in the field of lithium ion battery because of its structure stability,good safety,long cycle life,low-cost and environmentally friendly.Compared to LiFePO4,LiMnPO4 gives a much higher potential plateau and larger energy density.However,poor electrochemical performance limits its practical application.Synthesis of nanostrucutrual LiMnPO4 is an effective approach to improve its performance.Deep eutectic solvents(DESs)have been investigated as a sustainable media to overcome the limitations of ionic liquids(ILs).DESs have similar characteristics to traditional ILs.Comparing with traditional ILs,DESs are easy to make by mixing two widely available,low-cost starting materials,and are more suitable for large scale synthesis.Thus,DESs have widespread applications in the fields of chemistry,including synthesis,metal deposition,nanomaterials,gas adsorption,analysis and electrochemistry.However,the synthesis of nanostructural electrode materials for lithium ion battery in DESs has been seldom reported.In this work,a chloride/ethylene glycol-based deep eutectic solvent(DES)was applied to prepare nanostrucutral LiMnPO4/C using LiOH·H2O,H3PO4,MnSO4·H2O as the raw materials under atmospheric pressure.The effects of the heating method,reaction temperature,reaction time,sinter temperature and sinter time on the structure,morphology and elechemical performance of the prepared LiMnPO4/C were investigated.Nano rod-like LiMnPO4/C can be prepared by a conventional heating method in chloride/ethylene glycol-based DES,involving a formation of rod-like LiMnPO4 at 130 ? for 4 h and a subsequent heat treatment of LiMnPO4 rods/sucrose mixture at 600 ? for 5 h.The rod-like LiMnP04/C particles have a length of 80-110 nm and a diameter of 30-50 nm.As-synthesized LiMnP04/C nanorods deliver a discharge capacity of 127 mAh·g-1 with a capacity retention ratio of approximately 93%after 100 cycles at 1C.Nano-spindle LiMnPO4 can be prepared using a microwave-heating method at 130 ? for 30 min.The spindle-like LiMnP04/sucrose mixture was annealed at 600 ? for 5 h to get LiMnP04/C nano-spindles.The spindle-like LiMnP04/C powders have a length of?175 nm and a width of?45 nm.The prepared LiMnPO4/C nano-spindles exhibit a discharge capacity of 129 mAh·g-1 with a capacity retention ratio of approximately 97%after 100 cycles at 1 C.In short,chloride/ethylene glycol-based DES can act as a new crystal-face inhibitor to adjust the oriented growth and morphology of LiMnPO4/C.Furthermore,DESs provide a new approach to control the size and morphology of the particles,which has a wide application in the synthesis of electrode materials with special morphology.