Synthesis,Modification And Electrochemical Performance Of Limn₂O₄ Cathode For Aqueous Li-Ion Battery

With the continuous development of new energy industry,the requirements of energy storage device is increasing faster.Lithium-ion batteries become a reliable energy storage devices because of its high energy density and operating voltage.However,the use of organic electrolytic limits the large-scale use of Li-ion battery because of its high production costs,environmental pollution and etc.In 1994,Dahn et.al.proposed the concept of using aqueous solution as the electrolyte.Li Mn2O4 is a cathode material with high rate performance and high operating voltage,but the capacity of it fade quickly,so the material modification is particularly important.In this paper,We modified the material with 3 aspects: surface coating,crystalline doping and structure design,and the effect of modification is studied.Specific contents are as follows:(1).Surface coating: Li Mn2O4 was prepared by hydrothermal method and coated with Mg F2 to alleviate the dissolution of manganese during the cycle.The results of XRD test show there is no significant structure differences between the pristine and coated Li Mn2O4.The electrochemical test showed that the electrochemical properties of the composites were the best when the coating amount was 5wt%.The results of charge-discharge test showed that the discharge capacity increased from 84.2m Ah g-1 to 100.1m Ah g-1 after 100 cycles at 2C current density.The results of cyclic voltammetry and AC impedance tests showed that Mg F2 coating stabilizes the spinel structure of the material.(2).Crystalline doping: Na-doped Li1-x Nax Mn2O4 materials were prepared by a one-step sol-gel method.The structure of Li1-x Nax Mn2O4 after complete delithiation is stabilized by Na ion doping.The results show that Na occupies the tetrahedral sites of Li in the original lattice,and the remaining Na ion,which do not participate in the electrochemical deintercalation,can remain in the lattice of the material to stabilize the structure of the material after the lithium is completely delithiated.Electrochemical tests revealed that the material exhibited the best performance when x = 0.03.The capacity retention of Li0.97Na0.03Mn2O4 was increased from 51.2% to 84.1% after 100 cycles at 2C current density.The rate performance at 10 C current density increased from undoped 52.1 m Ah g-1 to 79.0 m Ah g-1.This is mainly because Na doping increased the lithium diffusion coefficient and stabilized the spinel structure.(3).Structure design: Li Mn2O4 with porous morphology was synthesized by using porous Mn2O3 as precursor.The porous morphology was used to provide a new channel for the transport of lithium ions,so as to improve the rate performance of the material.which provides a new channel for the transport of lithium ions,thus improving the rate performance of the material.The results show that the discharge capacity increases from 49.2m Ah to 62.1m Ah g-1 at 10 C rate.The cyclic voltammetry results show that the structure can increase the diffusion coefficient of lithium ion,decrease the polarization of the material,AC impedance tests revealed that this porous structure provides new channels for the transport of lithium ions,accelerating the diffusion of lithium ions.