Meihong Liu

Effect of magnesium doping on properties of lithium-rich layered oxide cathodes based on a one-step co-precipitation strategy

A Mg-doped lithium-rich layered oxide material is successfully synthesized via a co-precipitation process and a subsequent high-temperature solid state method. The chemical composition, structural characteristics and elemental distribution of the Mg-doped lithium-rich layered oxide material are investigated by inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDXS). The results show that Mg is effectively and equably doped into the samples, which can replace partially Li+ in the cathode material. The electrochemical properties of the Mg-doped lithium-rich layered oxide material are evaluated and compared with those of the conventional Li1.5[Mn0.75Ni0.25]O2+δ cathode material. It can be found that the Mg-doped lithium-rich layered oxide material exhibits excellent electrochemical performance. It can deliver a high initial discharge capacity of 248.6 mA h g−1 and an improved initial coulombic efficiency of 87.9% at 0.1C with a cut-off voltage of 2.0–4.6 V. Moreover, the capacity retention reaches a relatively high value of 94.2% after 200 cycles at 0.5C. In contrast, the capacity retention of conventional Li1.5[Mn0.75Ni0.25]O2+δ is only 59.6%. In addition, the Mg-doped lithium-rich layered oxide material also shows excellent rate capability, which can display a discharge capacity of 130.1 mA h g−1 even at 10C and a capacity retention of 92.6% after 100 cycles at 5C. The enhanced electrochemical properties of the Mg-doped lithium-rich layered oxide material could be attributed to the introduction of Mg, which can effectively mitigate the structural deterioration of the material and facilitate the diffusion coefficient of Li+ during cycling.

Preparation and performance of 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 with a fusiform porous micro-nano structure

A new lithium-rich layered cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 with a porous fusiform micro-nano structure has been successfully synthesized via a facile co-precipitation method followed by high temperature calcination. X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDXS) are used to characterize the chemical composition, structure, morphology and elemental distribution of the as-prepared lithium-rich layered material. It can be found that the as-prepared material presents a fusiform morphology and consists of interconnected nanosized subunits with a highly porous structure. The electrochemical measurements reveal that the material can deliver a high initial discharge capacity of 294.8 mA h g−1 and an excellent capacity retention of 87.1% after 200 cycles at 0.5C between 2.0 V and 4.6 V. In particular, even at a high rate of 10C, the material can still deliver a high discharge capacity of 139.5 mA h g−1. The excellent electrochemical performances can be ascribed to the unique fusiform porous micro-nano structure, which can facilitate the diffusion of lithium ions and enhance the structural stability of the lithium-rich layered cathode materials.

The effects of LiTi2(PO4)3 modification on the performance of spherical Li1.5Ni0.25Mn0.75O2+δ cathode material

The spherical layered Li1.5Ni0.25Mn0.75O2+δ cathode material is successfully modified with a LiTi2(PO4)3 (LTP) coating through a facile hydrothermal route. The effects of LTP modification on the structure, morphology and electrochemical performance of Li1.5Ni0.25Mn0.75O2+δ cathode material are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and charge–discharge tests. The results reveal that, among all the as-prepared samples, the sample modified with 3 wt% LTP delivers the highest reversible capacity of 254.9 mA h g−1 at 0.1C and excellent capacity retention of 95.8% after 100 cycles at 0.5C in a voltage range of 2–4.6 V. Additionally, the lithium-rich cathode material modified by LTP also exhibits superior rate capability with a capacity of 103.2 mA h g−1 even at a high discharge rate of 10C. The enhanced rate capability and cycling performances are attributed to the surface protective layer of LTP, which not only protects the surface of the active materials from electrolyte corrosion but also reduces the charge transfer resistance. Therefore, the modification with LTP of spherical lithium-rich cathode materials will be a promising technical route for the preparation of high performance lithium-ion battery cathode materials.

Facile synthesis and performance of Na-doped porous lithium-rich cathodes for lithium ion batteries

Na-doped porous lithium-rich (Li-rich) cathode microspheres (∼1 μm) were firstly prepared via the solvothermal method and subsequently a high-temperature calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption–desorption isotherms were used to characterize the structure and morphology of the as-prepared cathode material. It has been found that the as-prepared material has an obvious internal porous structure with the existence of 5 at% Na ions. Besides, the obtained cathode material possesses excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 305.2 mA h g−1 between 2.0 V and 4.6 V at a rate of 0.1C at room temperature and the retention of the capacity is still as high as 88.2% after 200 cycles. Furthermore, the electrochemical impedance spectroscopy (EIS) results also show that the introduction of Na ions can decrease the charge transfer resistance of the as-prepared cathode material. The excellent electrochemical performance of the as-prepared cathode material can probably be attributed to the improved stability of the bulk lattice and the expanded Li slab space, which facilitates lithium ion diffusion and effectively enhances the stability of the layered structure of the materials.