Research On The Composition,Structures And Electrochemical Properties Of The Mn-based Transition-metal Oxides As Cathodes For Lithium-ion Batteries

The high energy density of Li-ion batteries have facilitated the development of mobile electronic equipment and attracted people’s attention due to its advantages towards renewable energy, low cost, safe characters, environment friendly and so on. Moreover, the high energy and power density Li-ion batteries (LlBs) are the key technique of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs). To address the capacity dilemma, researchers have turned their focus on the Li-rich Mn-based layered oxides and LiNi0.5Mn1.5O4 as the alternative promising cathode materials.The Li-rich Mn-based layer materials xLi2MnO3·(1-x)LiNi0.5Mn0.5O2 (x=0～0.7) were successfully synthesized and systematically studied as one of the potential high capacity cathode materials for Li-ion batteries. The experimental results show that the relative content of Li2MnO3 for xLi2MnO3·(1-x) LiNi0.5Mn0.5O2 have a large impact on the structure and electrochemical properties. During rate tests, the specific capacities under different charging rate for each sample roughly improved with the increase of Li2MnO3 containment (equal to the x value) and reaching to the maximum around x= 0.5. However, keep on increasing Li2MnO3 content (x> 0.5), the electrochemical performance of the materials became worse which maybe caused by the structural change during the process of Li+ extraction/insertion. This tendency also existed during cycling test up to 50 cycles. Further analysis of sample xLi2MnO3·(1-x) LiNi0.5Mn0.5O2 (x=0.5) using in-situ XRD as implement disclosed the advanced electrochemical performance can be ascribed to the reversible of Li2MnO3. Thereby, these results indicate the electrochemical performance of xLi2MnO3·(1-x) LiNi0.5Mn0.5O2 could be improved by optimized the content of Li2MnO3, leading to the potential use as high capacity Li-ion batteries.Spinel compound LiNi0.5Mn1.5O4 with high capacity and high rate capability was synthesized by solid-state reaction. The MnO2、Ni(Ac)2·4H2O and LiAc·2H2O as a starting material by means of ball-milling auxiliary sample preparation. Then examines the calcination atmosphere, temperature and cooling conditions on the electrochemical properties of the product. We have measured samples through constant current charge-discharge tests. It is easy to see that with the calcination temperature increasing, the capacity of discharge of the samples is improved, and the sample exhibits a typical cubic spinel structure with a space group of Fd3m. Electrochemical tests demonstrate that the sample obtained possesses high capacity and excellent rate capability. When being discharged at a rate of 0.1 C after 8 cycles, the as-prepared LiNi0.5Mn1.5O4 powders can deliver a capacity of 114.5 mAh g-1. The calcined under an oxygen atmosphere or slow cooling treatment can significantly improve the cycling performance,which shows to be a promising cathode material for high-power battery.