| Layered xLi2MnO3(1-x)LiMO2(M=Ni,Co,Mn) materials have been the focus of cathodematerials and are hoped to be the mainstream commercial cathode material for Li-ion battery, due totheir high specific capacity and low price, etc. In this paper, we focused on Li[Li0.13Co0.61Mn0.26]O2andLi[Li0.2Co0.4Mn0.4]O2two kinds of commercial cathode materials, studied their behavior and tried ameasurement method of electrochemical kinetics parameters to devote to get the faster and more precisemeasurement data, and can be easily applied to the industrial experiment.Two kinds of lithium rich manganese based cathode materials Li[Li0.13Co0.26Mn0.61]O2andLi[Li0.2Co0.4Mn0.4]O2were successfully synthesized via sol-gel method by using transition metal acetate,lithium acetate and citric acid as raw material. The as-prepared materials were characterized by X-raydiffraction (XRD), scaning electron microscopy (SEM), and electrochemical performance tests. Theresult of XRD proved the structure of lithium rich manganese based cathode materials is layeredsolid-solution. The SEM image indicated that the size of primary particles of materials is from100nm to250nm. The change of charge transfer impedance (Rct) of lithium rich manganese based cathodematerials during charging in the same cycle was studied through chronopotentiometry. The resultsindicate that during charging process, Rct reaches maximum values about2164Ω~4341Ωand4254Ω~6741Ω respectively, at scope of state-of-charge (SOC) form30%to50%and exhibited a lowerrelative value, from221to2261Ωand from303to2219Ω, at rest scope of SOC.Cyclic voltammetry test results show that, when the cut-off voltage is higher than4.4V, oxygen isliberated from Li-rich manganese-based material; cobalt oxidation peak potential is~4.11V, thereduction peak potentials is~3.75V; and manganese oxidation peak potential is~4.0V, the reductionpeak potential is~3.25V, and~2.75V which is related with Mnn+reduction forming spinel structure. Theresults show that the component of LiMO2in high amounts can improve the exchange current densityand the rate capability of lithium rich manganese based materials, and increasing the component ofLi2MnO3will improve the cycle stability in a low rage.By changing the ratio of Li[Li0.13Co0.26Mn0.61]O2(i.e. materials A) and Li[Li0.2Co0.4Mn0.4]O2(i.e.material B), two kinds of lithium rich manganese base material, we prepared QRASPE(quasi-randomassembled single particle electrode) which was experienced in3.0~4.8V voltage range, at the scanningspeed of0.1mV/s with cyclic voltammetry.And further manipulation of the data which was deductedbackground effect, we can find that QRASPE has more advantages than large-area porous electrodes. Oxidation/the reduction peak is more sharp with QRASPE, so it is more easy to judge The Fermienergy of the transition metal. The oxygen release occurred in~4.43V formation a significant oxidationpeak of Li2MnO3; and the oxidation and reduction peak of cobalt element was in~4.10V and~3.89Vrespectively; and the reduction peak of manganese element was in the~3.25V. In addition the furtheranalysis of the safety cut-off voltage of the materials In the process of charging: material Ais4.32V, andmaterial B is4.33V. In the actual application process, determination of the safety cut-off voltage not onlycan insure the safe use, but also can make full use of the battery and save energy.The use of green energyof lithium-ion battery will play an activerole in the environment protection. |
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