Huali Zhu

A hydrolysis-hydrothermal route for the synthesis of ultrathin LiAlO2-inlaid LiNi0.5Co0.2Mn0.3O2 as a high-performance cathode material for lithium ion batteries

We present a novel hydrolysis-hydrothermal approach to using lithium residues on the surface of LiNi0.5Co0.2Mn0.3O2 as raw materials to synthesize ultrathin LiAlO2-inlaid LiNi0.5Co0.2Mn0.3O2 cathode materials, for the first time. High-resolution transmission electron microscopy (HRTEM) and fast Fourier transform (FFT) analysis indicate that the spherical particles of LiNi0.5Co0.2Mn0.3O2 are completely coated by crystalline LiAlO2 with an average thickness of 4 nm; cross-section SEM and corresponding EDS results confirm that partial Al3+ ions are doped into the bulk LiNi0.5Co0.2Mn0.3O2 with gradient distribution. Electrochemical tests show that the modified materials exhibit excellent reversible capacity, enhanced cyclability and rate properties, combining with higher Li ion diffusion coefficient and better differential capacity profiles compared with those of the pristine material. Particularly, the 2 mol% LiAlO2-inlaid sample maintains 202 mA h g−1 with 91% capacity retention after 100 high-voltage cycles (with 4.6 V charge cut-off) at 1 C. The enhanced electrochemical performance can be ascribed to the removal of lithium residues and the unique LiAlO2-inlaid architecture. The removal of lithium residues are believed to decrease side reactions between Li2O and the electrolyte, while the unique LiAlO2-inlaid architecture can buffer the volume change of core and shell during cycles, enhance the composites lithium ion diffusion ability and inherit the advantages of LiAlO2 coating and doping.

Mitigating capacity fade by constructing highly ordered mesoporous Al2O3/polyacene double-shelled architecture in Li-rich cathode materials

Lithium-rich layered oxides, xLi2MnO3·(1 − x)LiMO2 (M = Ni, Mn, Co), have been considered as one of the most promising cathode active materials for rechargeable lithium-ion batteries due to their high capacity over 250 mA h g−1 between 2.0 and 4.8 V. However, the commercialized application of these cathodes has so far been hindered by their severe capacity fading and transition metal dissolution during high voltage cycling (>4.5 V vs. Li/Li+). To overcome this barrier, a double-shelled architecture consisting of an inner conductive polyacene layer and an outer mesoporous Al2O3 layer is constructed. A polyacene layer with high electron conductivity is first coated on the surface of a 0.5Li2MnO3·0.5LiNi0.5Co0.2Mn0.3O2 cathode material, followed by a hydrothermal method combined with an in-sol treatment to produce a highly ordered mesoporous Al2O3 layer. Compared to previous studies, this double-shelled architecture has substantially improved the electrochemical performance of the 0.5Li2MnO3·0.5LiNi0.5Co0.2Mn0.3O2 cathode material. Two striking characteristics are obtained for this double-shelled lithium-rich layered oxide cathode material: (1) the electrochemical capacity is greatly improved, reaching 280 mA h g−1 (2.0 V–4.8 V at 0.1 C) and (2) the transition from the layered phase to spinel is delayed, leading to a superior capacity retention of 98% after the 100th cycle.

Characterization of Na-substituted LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium-ion battery

Highly crystalline layered Li1−xNaxNi1/3Co1/3Mn1/3O2 (x = 0, 0.001, 0.01, 0.03, 0.05) materials are synthesized by molten salts method and characterized by scanning electron microscopy, inductively coupled plasma (ICP), X-ray diffraction, Rietveld refinement, and electrochemical measurement, respectively. ICP, SEM, and EDS results show that Na ions are incorporated in LiNi1/3Co1/3Mn1/3O2. Rietveld refinement results show that suitable Na substitution leads to stable layered structure by full Na occupying in Li layer and further attributes to low cation mixing. Electrochemical studies demonstrate that the Na-substituted LiNi1/3Co1/3Mn1/3O2 shows improved rate capability and cycling performance compared to that of pure LiNi1/3Co1/3Mn1/3O2.

Understanding the Impact of K-Doping on the Structure and Performance of LiFePO4/C Cathode Materials

The K-doped Li1-xKxFePO₄ (x = 0, 0.005, 0.01, and 0.02) samples were synthesized successfully via a solid-state method, and the electronic structures of the samples were calculated by the first-principles based on density functional theory. Theoretical calculations show that the bandwidth of Li1-xKxFePO₄ decreases with the increase in K+ doping, which is consistent with the experimental results. It was demonstrated that Li0.995K0.005FePO₄ delivers higher capacity retention with 92.7% after 100 cycles compared with LiFePO₄ (86.3%) at 1 C and shows better high-rate performance with capacities of 151.9, 151.8, 149.2, 128.3, and 84.6 mAh·g-1 at current densities of 0.1 C, 0.2 C, 0.5 C, 1 C, and 3 C; the corresponding values for LiFePO₄ were 153.2, 136.5, 125.9, 111.5, and 66.0 mAh·g-1. Owing to the expanded Li ion diffusion pathway, EIS analysis showed that the lithium ion diffusion coefficient of LiFePO₄ doped with K ion was significantly improved compared to LiFePO₄; the values were 1.934×10-13 and 1.658×10-12 cm²·s-1, respectively. Additionally, Li0.995K0.005FePO₄ showed a lower charge transfer resistance (300.2 Ω compared to 407.1 Ω of LiFePO₄).