Honglei Liu,Meng Li,Mingwu Xiang,Junming Guo,Hongli Bai,Wei Bai,Xiaofang Liu
Various Li-rich spinel Li 1+ x Ni 0.05 Mn 1.95- x O 4 (0 ≤ x ≤ 0.10) cathode materials with a truncated octahedron were synthesized by a solution combustion method. The relationship of crystalline structure, particles morphology and electrochemical properties of the as-prepared samples was investigated via a series of physicochemical characterizations. The Li-Ni co-doping changes the lattice parameters and atomic configuration, whilst resulting in a contraction of unit cell dimension and giving rise to a variation of bond length. In this regard, the shrinkage of octahedral MnO 6 provides a robust structure and the expansion of tetrahedral LiO 4 facilitates a fast electrochemical process. Additionally, the resulted polyhedral Li 1+ x Ni 0.05 Mn 1.95- x O 4 samples present the exposed (1 1 0), (1 0 0), and (1 1 1) crystal planes, which provide the favorable Li + ions diffusion/transmission channel and alleviate Mn dissolution. Owing to these merits of polyhedral structure and Li-Ni co-doping, the optimized Li 1.02 Ni 0.05 Mn 1.93 O 4 exhibits good electrochemical performance with high initial discharge capacity of 119.8, 107.1 and 97.9 mAh·g −1 at 1, 5 and 10 C, respectively. Even at a high current rate of 15 C, an excellent capacity retention of 91.7% is obtained after 1000 cycles, whilst the high temperature performance was also improved.
Porous spherical γ-alumina supports play the key role in the petroleum reforming industry with strict requirement in hydrothermal stability of pore structure. Here, a series of pseudo-boehmite samples with different crystal orientations were synthesized in a separate nucleation and aging steps method by adjusting the rotating speed. The pseudo-boehmite (PB-1000) at 1000 rpm yields a high (0 2 0) plane proportion of 44.52 %, which is comparable with that of 43.91 % for the Sasol Boehmite (SB) powder. The Al 2 O 3 -1000 from the PB-1000 demonstrated the highest content of γ-Al 2 O 3 phase, the lowest surface hydroxyl number of 1.56/nm 2 , and the highest hydrothermal stability with the retention rate of 75.0 % (174 m 2 ·g −1 ) at 600 °C under water vapor for 120 h, which is comparable to that of 72.3 % (191 m 2 ·g −1 ) for the Sasol sample. It is the first time to investigate hydrothermal stability of alumina from the content of γ-Al 2 O 3 phase and the surface hydroxyl groups.
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