He Jielong,Bai Zhe,Huang Xinping,Zhang Zhengyu,Lu Lu,Li Jun
In this work, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 was prepared by the sol–gel method and coated with FePO 4 . The experimental results show that the material surface is uniformly coated with FePO 4 . A small amount of coating will not change the layered structure of the material. Among them, the material with 5% FePO 4 coating has the best performance. The first charge and discharge specific capacity at 0.1 C current density is 324.4 mAh g −1 and 280.4 mAh g −1 , respectively. And the first coulomb efficiency is 86.4%, which is significantly higher than 75.6% of the pristine material. The improvement of the first charge–discharge performance of the coating material is due to the decrease of discharge voltage plateau and the redox of FePO 4 with electrochemical activity. When the FePO 4 coating content is 5%, the cycling performance of the material at 0.2 C current density is the best. After 100 cycles, the capacity decays from 268.4 to 232.9 mAh g −1 , and the capacity retention rate is 86.78%, which is higher than 60.58% of the pristine sample. The discharge specific capacity of 5% coated material at 5 C rate is 134.8 mAh g −1 , which is higher than 95.3 mAh g −1 of the pristine material. Graphical
Wang Li-Zhen,Yang Wei,Lv Teng-Fei,Gao Ke-Zheng,Yan Ji
In this paper, core-shell like LiAlO 2 -coated Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 composite was synthesized by an improved solvothermal method. The surface of the material becomes rough after LiAlO 2 coating with a thickness of 5–10 nm. Meanwhile, the surface-coating component with the layer structure α-LiAlO 2 can change the dispersion of transition metal elements. When tested in 2.0–4.8 V at 0.05 °C, the initial discharge capacity of the LiAlO 2 -coated sample is 206.4 mAh g −1 with the columbic efficiency of 78.0%, which is higher than that of the pristine Li-rich Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 sample. Further tested under 1 C rate, the coated sample possesses 151.4 mAh g −1 of specific capacity and maintains 149.0 mAh g −1 after 50 cycles with the capacity retention of 98.4%. The improved reversible capacity, rate capability, and cycling durability of the Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 material are attributed to the synergistic effect of surface coating of highly Li-conductive LiAlO 2 and the fuzzy interface between LiAlO 2 and Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 .
Huang Xinping,Zhang Zhengyu,He Jielong,Bai Zhe,Lu Lu,Li Jun
Abstract Li-rich layered oxides are identified as the most promising cathode material for lithium ion batteries due to their high specific capacity and energy density. However, capacity fading, voltage decay and inferior rate capability have restricted its development in industry. Herein, we developed a novel cation/anion (chromium/fluorine) co-doping methods to enhance the electrochemical performance of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 . X-ray diffraction, scanning electron microscopy, and transmission electron microscopy images reveal the perfect crystal structure. The Cr and F co-doped Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 shows the best discharge specific capacity, the highest rate performance and the lowest voltage decay. The initial discharge capacity is improved from 264.4 to 273.7 mAhg −1 . The capacity retention ratio is enhanced from 78.84% to 94.46% after 50 cycles. The R ct (charge transfer resistance) is decreased from 556.1Ω to 199.5Ω. The lower R ct and higher D Li+ of the Cr and F co-doped Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 contribute to the excellent rate capability. More importantly, the co-doped material exhibits elevated discharge voltage and shows lower discharge mean voltage decay (0.2945 V) than that of the pristine material (0.4396 V). These results fully suggest that cation and anion doping could effectively improve the electrochemical performances of Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 . Graphical Abstract
Lithium-rich layered oxide cathode material Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 has been successfully synthesized via a self-template method followed with sol-gel reaction, microspheres consisting of three-dimensional (3D) nanothorn MnO 2 are used as the template and Mn source. The as-prepared sample (denoted as LNCM-T) exhibits well-layered structure and high crystallinity , which is confirmed by XRD and HRTEM . The results of electrochemical performances show that the LNCM-T sample has excellent high-rate capability with a discharge capacity of 159.7 mA h g −1 at a current density of 1250 mA g −1 . Besides, it delivers a high initial Coulombic efficiency of 84.3% with a discharge capacity of 243.8 mA h g −1 at room temperature . The remarkable cycling stability and excellent rate capability of LNCM-T sample are ascribed to the enhanced layered structural stability, short lithium-ion diffusion path and reduced charge transfer resistance .
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