Synthesis And Electrochemical Performance Of Lithium Manganese Phosphate Composite Cathode Materials For Lithium-ion Battery

The olivine LiMnPO₄ has advantages in the field of high energy density,high discharge potential,and high theoretical capacity,which is regarded as one of the valuable cathode materials for lithium ion batteries.However,its structure leads to poor ionic and electronic conductivity,which restricts its development.To solve this problem,a series of binary composite materials?1-x?LiMnPO₄·xLiFePO₄ and?1-x?LiMnPO₄·xLi₃V₂?PO₄?₃ and ternary composite materials?1-x-y?LiMnPO₄·x LiFePO₄·yLi₃V₂?PO₄?₃ were designed and prepared in this paper,and the electrochemical performance was studied by charge-discharge test,CV and EIS.?1?The design,preparation,and electrochemical performance of phosphate-based?1-x?LiMnPO₄·xLiFePO₄/C binary composite materials: a series of binary composite materials?1-x?LiMnPO₄·xLi FePO₄ were prepared by sol-gel method.The doping of Fe²⁺ has reduced the electrochemical polarization,resulting in the improvement in the following aspects such as the reversibility of electrodes,the ability of delithiation/lithiation,and the ionic conductivity.The 8LiMnPO₄·5LiFePO₄/C composites have the lowest charge transfer impedance.The results showed that the electrochemical performance of 8LiMnPO₄·5LiFePO₄/C was the best,and the discharge specific capacity of the first cycle reached 169.8 mAh?g^-1 and still maintained 160.3 mAh?g^-1 at 0.05 C after 50 charge-discharge cycles,the cyclabilities are excellent under various rates,suggesting the conductivity of LiMnPO₄ was greatly improved after the introduction of LiFePO₄.?2?The design,preparation,and electrochemical performance of phosphate-based?1-x?Li MnPO₄·xLi₃V₂?PO₄?₃/C binary composite materials: a series of binary composite materials?1-x?LiMnPO₄·xLi₃V₂?PO₄?₃/C were prepared by sol-gel method.It was found that Li₃V₂?PO₄?₃ and LiMnPO₄ were successfully combined and exist in +3 valence.What's more,Li₃V₂?PO₄?₃ can facilitate charge transport and the diffusion of Li ions,so as to improving the electrochemical properties of LiMnPO₄ material.The results showed that the electrochemical performance of 7LiMnPO₄·Li₃V₂?PO₄?₃/C was the best,and the discharge specific capacity of the first cycle reached 158.8 mAh?g^-1 and still maintained 155.9 mAh?g^-1 at 0.05 C after 50 charge-discharge cycles,suggesting the conductivity of LiMnPO₄ was greatly improved after the introduction of Li₃V₂?PO₄?₃.?3?The design,preparation,and electrochemical performance of phosphate-based?1-x-y?LiMnPO₄·xLiFePO₄·yLi₃V₂?PO₄?₃ ternary composite materials: a series of ternary composite materials of?1-x-y?LiMnPO₄·x LiFePO₄·yLi₃V₂?PO₄?₃ were prepared by sol-gel method.The results showed that the initial discharge specific capacity of 7LiMnPO₄·4Li FePO₄·3Li₃V₂?PO₄?₃/C ternary composite materials reached 159.4 mAh·g^-1 and the capacity retentions still maintained 96.4% after 50 charge-discharge cycles at 0.05 C.And the initial discharge specific capacity of 5LiMnPO₄·3Li₃V₂?PO₄?₃·2Li FePO₄/C ternary composite materials reached 155.0 mAh·g^-1 and the capacity retentions still maintained 98.2% after 50 charge-discharge cycles at 0.05 C.So the electronic conductivity,lithium ion diffusivity rate,discharge specific energy and high rate electrochemical performance of LiMn PO4 were improved by being added by LiFePO₄ of high electronic conductivity and Li₃V₂?PO₄?₃ of high lithium ion diffusivity rate,which shows great meanings of practical application.