Synthesis And Electrochemical Performances Of Layered Oxide Cathode Materials For Li/Na-ion Batteries

Lithium-ion batteries (LIBs) have been widely used in energy storage and conversion field with high specific energy, long lifespan, high efficiency, high safety performance. However, the large-scale applications are limited by the high cost and the finite resource of lithium. On the basis of material abundance, cheap price and standard electrode potential, rechargeable sodium batteries are flourishing. From the point of view of the development of lithium/sodium ion batteries, the electrochemical performances of the batteries largely depend on the structures and properties of the electrode and electrolyte materials being used, especially the electrode materials. Layered cathode material of lithium/sodium ion batteries is one of the older research systems. However, the disadvantages of the single layered phase may lead to low specific and rate capacity or low power performance. Herein, we tried to control the overall performance combined with multiphase structure and micro-nano technology, which is considered as one of the most effiencient methods to improve the electrochemical performance of the electrode material. In this paper, we provided a detailed study of the structures and electrochemical properties of Fe-Mn-based layered lithium ion cathode material and Ni-Mn-based micro-nanostructured layered sodium ion cathode material and obtained some interesting results as follows:1. LiFexMn1-xO2 (O≤x≤1) compounds were synthesized by the co-precipitation method. Electrochemical tests show that the LiFe0.25Mn0.75O2 composite has a maximum reversible capacity of 180mAh/g at 0.1C. XRD results show that the LiFexMn1-xO2 (0<x<1) samples actually have multiple crystal phases. It was composed of three phases, the spinel phase (LiMmO4 and the Li-rich phase (Li2MnO3) and the layered one (LiFeO2). Moreover, X-ray absorption spectroscopy (XAS) reveals that the Mn-phase and the Fe-phase are randomly stacked in the samples. The work shows the doping of Fe influences the crystal phase and the local structure of the Mn-phase upon the samples and then tunes the electrochemical performances of the cathode materials, giving an optimal proportion (x=0.25) of the spinel and Li-rich and layered phases.2. Single and twinborn microspheres of ternary transition metal carbonate precursors assembled with nanocubes were synthesized by the urea-assisted solvothermal method. Layered cathode material Na0.7Ni1/6Co1/6Mr12/3O2 was subsequently prepared using the precursors synthesized above. The micro-nano material shows 200mAh/g discharge capacity at 0.05C and 120mAh/g at 2C, which is benefit of the large specific surface of nanostructurc and Na diffusion kinetics of the porous architectures of the micro-nano structure.