Research Of High Performance LiMn₂O₄ Composite In Lithium Ion Batteries’ Modification

With further exacerbating oil crisis, the excessive use of non-renewable resources, represented by oil and a sharp deterioration in living environment force people to seek a renewable energy utilization method. Synthesis process of spinel lithium manganese cathode materials showing good cycle performance is simple. Adding rich raw material sources, they has been the focus of research in the last decade. However, those materials have some problems, such as high current charge-discharge capability and high-temperature cycle performance. Furthermore, it is difficult to resist impurities like Mn2O3, phase nonuniform and grain shape without rules. That is because in the late discharge it is easy to occurred disproportionation of high concentrations of Mn3+, 2Mn3+(s) â†' Mn4+(s) + Mn2+(l), and the Mn2+ is dissolved in the electrolytic solution, which makes the reversible reaction fail and the capacity of lithium manganese acid seriously attenuate. At high temperature and high current charge and discharge, spinel structure of lithium manganate is damaged, increasing the battery impedance value and decreasing the coulomb efficiency.In this paper, spinel lithium manganese oxide cathode materials were prepared by high-temperature solid-phase and sol-gel method. The structures and morphologies of them were characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM) techniques. And the electrochemical performance was analyzed using cyclic voltammetry(CV), impedance spectroscopy(EIS) and battery charge and discharge tests.This article mainly uses doped with coated experimental method. Spinel lithium manganese oxide was doped with metal cations to replace part of the Mn3+, which, on the one hand, can reduce the concentration of Mn3+ post-discharge, weaker Taylor effect and improve the structural stability and cycle characteristics of the battery, on the other hand, the addition of suitable metal cations improve the voltage plateau of lithium manganese oxide. Coated conductive carbon black and graphene nano-particles on the cathode material can increase the conductivity of lithium manganese oxide cathode materials, reducing the chance of active material in contact with the electrolyte and improving the performance of the cell cycle. The results show that morphology structure and electrochemical performance of battery cathode materials by doping and coating, has been improved. High-current battery charge and discharge performance, cycle performance and battery capacity has enhanced. Especially, after Cr3+ doped, and then the graphene surface coating treatment, the cycle performance has been greatly improved, namely after 100 cycles, the capacity retention rate becoming 98.10% and large-current discharge capacity of 128mAh/g in 5C.