Haiping Jia

Enhanced electrochemical performance in lithium ion batteries of a hollow spherical lithium-rich cathode material synthesized by a molten salt method

A high voltage layered Li1.2Ni0.16Co0.08Mn0.56O2 cathode material with a hollow spherical structure has been synthesized by molten-salt method in a NaCl flux. Characterization by X-ray diffraction and scanning electron microscopy confirmed its structure and proved that the as-prepared powder is constituted of small, homogenously sized hollow spheres (1–1.5 μm). The material exhibited enhanced rate capability and high first cycle efficiency due to the good dispersion of secondary particles. Galvanostatic cycling at different temperatures (20, 40, and 60 °C) and a current rate of 2 C (500 mA·g−1) showed no significant capacity fade.

Facile Synthesis and Lithium Storage Properties of a Porous NiSi2/Si/Carbon Composite Anode Material for Lithium-Ion Batteries

In this work, a novel, porous structured NiSi2/Si composite material with a core-shell morphology was successfully prepared using a facile ball-milling method. Furthermore, the chemical vapor deposition (CVD) method is deployed to coat the NiSi2/Si phase with a thin carbon layer to further enhance the surface electronic conductivity and to mechanically stabilize the whole composite structure. The morphology and porosity of the composite material was evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption measurements (BJH analysis). The as-prepared composite material consists of NiSi2, silicon, and carbon phases, in which the NiSi2 phase is embedded in a silicon matrix having homogeneously distributed pores, while the surface of this composite is coated with a carbon layer. The electrochemical characterization shows that the porous and core-shell structure of the composite anode material can effectively absorb and buffer the immense volume changes of silicon during the lithiation/delithiation process. The obtained NiSi2/Si/carbon composite anode material displays an outstanding electrochemical performance, which gives a stable capacity of 1272 mAh g(-1) for 200 cycles at a charge/discharge rate of 1C and a good rate capability with a reversible capacity of 740 mAh g(-1) at a rate of 5C.

One-step synthesis of novel mesoporous three-dimensional GeO2 and its lithium storage properties

Novel mesoporous three-dimensional GeO2 was successfully synthesized by a facile one-step synthesis method followed by mixing with graphene using a spray drying process. The well-dispersed mesoporous GeO2 demonstrates a bean-like morphology (b-GeO2) with a particle size of 400 to 500 nm in length and 200 to 300 nm in diameter, in which mesopores with an average size of 3.6 nm are distributed. The b-GeO2 without any additional conductive surface layer shows a high reversible capacity for lithium storage of 845 mAh g−1 after 100 cycles, with nearly no capacity fading. When graphene was employed to be mixed with GeO2via a spray drying method, the electrochemical performance is further significantly improved. The b-GeO2/graphene composite electrode gives a higher de-lithiation capacity of 1021 mAh g−1, and the capacity retention is measured to be as high as 94.3% after 200 charge–discharge cycles for constant current cycling at 0.2 C, as well as an excellent rate performance, even displaying a reversible capacity of 730 mAh g−1 at a rate of 5 C.