Cheng-Gong Han

Improved electrochemical properties of LiMn2O4 with the Bi and La co-doping for lithium-ion batteries

A series of LiBixLaxMn2−2xO4 (x = 0, 0.002, 0.005, 0.010, 0.020) samples were synthesized by solution combustion synthesis in combination with calcination. The phase structure and morphology of the products were characterized by X-ray diffraction, scanning electron microscopy, and transition electron microscopy. The results demonstrated that a single-phase LiMn2O4 spinel structure was obtained for the LiBixLaxMn2−2xO4 (x = 0, 0.002, 0.005) samples, whereas impurities were observed for the LiBixLaxMn2−2xO4 (x = 0.010, 0.020) samples as a result of the doping limit. The electrochemical properties were investigated by galvanostatic charge–discharge cycling and cycling voltammetry in a voltage range of 3.2–4.4 V. The substitution of Mn3+ by equimolar Bi3+ and La3+ could significantly improve the structural stability and suppress the Jahn–Teller distortion, thereby resulting in improved electrochemical properties for the Bi and La co-doped samples in contrast with the pristine LiMn2O4 sample. In particular, the LiBi0.005La0.005Mn1.99O4 sample delivered a high initial discharge capacity of 130.2 mA h g−1 at 1C, and following 80 cycles, the capacity retention was as high as 95.0%. Moreover, it also presented the best rate capability among all the samples, in which a high discharge capacity of 98.3 mA h g−1 was still maintained at a high rate of 7C compared with that of 75.8 mA h g−1 for the pristine LiMn2O4 sample.

MnO nanocrystals incorporated in a N-containing carbon matrix for Li ion battery anodes

In this study, MnO nanocrystals incorporated in a N-containing carbon matrix were fabricated by the facile thermal decomposition of manganese nitrate-glycine gels. MnO/C composites with different carbon contents were prepared by controlling the initial ratio of manganese to glycine. The composition, phase structure and morphology of the composites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning and transmission electron microscopy, and thermogravimetric analysis. The results indicated that MnO nanocrystals were uniformly embedded in the N-doped carbon matrix. The carbon matrix could effectively enhance the electrical conductivity of MnO and alleviate the strain arising from the discharge/charge cycling. The composite materials exhibited high discharge/charge capacities, superior cycling performance, and excellent rate capability. A high reversible capacity of 556 mA h g−1 was obtained after 110 cycles of discharging and charging at a current rate of 0.5 A g−1. Even at a high current rate of 3 A g−1, the sample still delivered a capacity of around 286 mA h g−1. The easy production and superior electrochemical properties enables the composites to be a promising candidate as an anode alternative for high-performance lithium-ion batteries.

Controlled synthesis of LiNi0.5Mn1.5O4 cathode materials with superior electrochemical performance through urea-based solution combustion synthesis

High-voltage LiNi0.5Mn1.5O4 cathode materials were synthesized using urea-based solution combustion synthesis combined with a calcination treatment. The morphology and particle size distribution of the products were considerably dependent on the amount of urea fuel. The electrochemical characterization illustrated that the sample that was produced with a fuel ratio of ϕ = 0.5 had a homogenous particle size distribution of approximately 8 μm, and showed the best cycling and rate performance. LiNi0.5Mn1.5O4 with two different structures of disordered Fdm and ordered P4332 were obtained by controlling the calcination process. The samples, which were calcined at 800 °C with fast cooling, presented a disordered structure of Fdm, and the samples, which were calcined at 800 °C with slow cooling and reannealing at 600 °C, demonstrated an ordered structure of P4332. The sample with a disordered structure exhibited a better electrochemical performance than the sample with an ordered structure. The disordered sample produced at ϕ = 0.5 presented a discharge capacity of 130.73 mA h g−1 and a capacity retention of 98.43% after 100 cycles at 1 C. Even at a higher current rate of 3 C, the sample still showed a high discharge capacity of 117.79 mA h g−1 and a capacity retention efficiency of 97.63% after 300 cycles.