Zhong-Feng Tang

Vanadium-doped lithium-rich layered-structured cathode material Li1.2Ni0.2Mn0.6O2 with a high specific capacity and improved rate performance

Fine powders of Li1.2Ni0.2Mn0.6−xVxO2 (x = 0, 0.002, 0.005, 0.01, 0.02) are prepared by a thermopolymerization method. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical measurements are carried out to characterize these samples. The V-doped samples show great improvement in rate performance and cycling stability, as well as mitigation of voltage decline during cycling. For the optimal composition Li1.2Ni0.2Mn0.59V0.01O2, it exhibits a discharge capacity of 245 and 118 mA h g−1 at 0.1C and 10C rates, respectively. It retains a capacity of 234 mA h g−1 at 0.1C after 188 cycles with a capacity retention of 95.5%. This study suggests that the partial substitution of Mn4+ with V5+ can improve both the rate capability and cycle stability of this high-capacity cathode material.

Surface Surgery of the Nickel-Rich Cathode Material LiNi0.815Co0.15Al0.035O2: Toward a Complete and Ordered Surface Layered Structure and Better Electrochemical Properties

A complete and ordered layered structure on the surface of LiNi0.815Co0.15Al0.035O2 (NCA) has been achieved via a facile surface-oxidation method with Na2S2O8. The field-emission transmission electron microscopy images clearly show that preoxidation of the hydroxide precursor can eliminate the crystal defects and convert Ni(OH)2 into layered β-NiOOH, which leads to a highly ordered crystalline NCA, with its (006) planes perpendicular to the surface in the sintering process. X-ray photoelectron spectroscopy and Raman shift results demonstrate that the contents of Ni2+ and Co2+ ions are reduced with preoxidization on the surface of the hydroxide precursor. The level of Li+/Ni2+ disordering in the modified NCA determined by the peak intensity ratio I(003)/I(104) in X-ray diffraction patterns decreases. Thanks to the complete and ordered layered structure on the surface of secondary particles, lithium ions can easily intercalate/extract in the discharging-charging process, leading to greatly improved electrochemical properties.

A potassium-rich iron hexacyanoferrate/dipotassium terephthalate@carbon nanotube composite used for K-ion full-cells with an optimized electrolyte

K-ion batteries, as an emerging battery system, have attracted tremendous attention in the research community. Herein, we report a K-ion full-cell based on a nano-sized K1.92Fe[Fe(CN)6]0.94·0.5H2O cathode, dipotassium terephthalate (K2TP)@carbon nanotube (CNT) anode and an optimized electrolyte. K1.92Fe[Fe(CN)6]0.94·0.5H2O delivers a high capacity of 133 mA h g−1 with 92.8% capacity retention after 200 cycles and high coulombic efficiency of 98.5%. The side reactions of K metal with the electrolyte are suppressed in KClO4/propylene carbonate (PC). The K2TP nanosheets grown in situ on the CNT show a high reversible capacity of about 250 mA h g−1 and an ultra-high rate capability. The full-cells based on them are well cycled in a DME-based electrolyte and show a great promise for large-scale energy storage.

A high energy density full lithium-ion cell based on specially matched coulombic efficiency

Nano-spherical Li-rich cathodes and MnxCo1−xO anodes are synthesized from as-solvothermal MnxCo1−xCO3 (x = 1, 0.8, and 0.5) precursors. Based on the half-cell studies of these materials, Li-rich 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2 with a high reversible capacity of 247 mA h g−1 and binary transition metal oxide Mn0.8Co0.2O with a reversible capacity of 759 mA h g−1 are selected respectively as the optimal positive and negative electrodes to construct a full cell. Such an electrode match-up, i.e. Li-rich/Mn0.8Co0.2O full cell (“N-cell”), allows no need for pre-activation of the metal oxide anode. This “N-cell” can deliver a high reversible capacity of 205 mA h g−1 and particularly rather high volumetric energy density, which is about 31% higher than that of a Li-rich/graphite full cell (“T-cell”). The special coulombic efficiency match-up and tailored microstructures and compositions of the electrode materials are all crucial to achieve such a high energy density.

A comparative study on nanocrystalline layered and crystalline cubic TiP2O7 for rechargeable Li/Na/K alkali metal batteries

We report, for the first time, that a nanocrystalline layered TiP2O7 as a cathode material for Li-, Na- and K-alkali metal batteries is prepared by a solvothermal process followed by a heat treatment at 600 °C. For comparison, a crystalline cubic TiP2O7 is also synthesized at 800 °C. It is clarified that the layered TiP2O7 is slightly poorer for lithium storage but much better for sodium and potassium storages than the cubic phase. The detailed electrochemical processes are investigated by means of ex situ XRD analyses. Different from the two-phase co-existence mechanism for the cubic phase, a solid-solution mechanism is identified for the layered phase to follow in the Li/Na/K intercalation reactions based on electrochemical and structural studies. To overcome the poor electronic conductivity limit for high rate applications, carbon coating is employed on the TiP2O7 samples. The carbon-coated layered phase TiP2O7 (600 °C) displays fairly reversible capacity close to 100 mA h g−1 in both Li and Na rechargeable alkali metal batteries. It is a promising electrode material for large energy storage systems.

A novel lithium-ion battery comprising Li-rich@Cr 2 O 5 composite cathode and Li 4 Ti 5 O 12 anode with controllable coulombic efficiency

Through meticulous design, a Li-lacking Cr2O5 cathode is physically mixed with Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 (LNCM) cathode to form composite cathodes LNCM@xCr2O5 (x = 0, 0.1, 0.2, 0.3, 0.35, 0.4, mass ratio) in order to make use of the excess lithium produced by the Li-rich component in the first charge-discharge process. The initial coulombic efficiency (ICE) of LNCM half-cell has been significantly increased from 75.5% (x = 0) to 108.9% (x = 0.35). A novel full-cell comprising LNCM@Cr2O5 composite cathode and Li4Ti5O12 anode has been developed. Such electrode accordance, i.e., LNCM@Cr2O5//Li4Ti5O12 (“L-cell”), shows a particularly high ICE of 97.7%. The “L-cell” can transmit an outstanding reversible capacity up to 250 mA h g−1 and has 94% capacity retention during 50 cycles. It also has superior rate capacities as high as 122 and 94 mA h g−1 at 1.25 and 2.5 A g−1 current densities, which are even better in comparison of Li-rich//graphite full-cell (“G-cell”). The high performance of “L-cell” benefiting from the well-designed coulombic efficiency accordance mechanism displays a great potential for fast charge-discharge applications in future high-energy lithium ion batteries.摘要本文将缺锂态的Cr2O5正极材料与Li1.2Ni0.13Co0.13Mn0.54O2(LNCM)富锂相正极材料进行物理混合, 形成了复合正极材料LNCM@xCr2O5(x = 0,0.1,0.2,0.3,0.35, 0.4), 从而在第一次充放电过程中达到有效利用富锂相所产生的不可逆的锂离子. 复合之后, LNCM半电池的首次库仑效率(ICE)得到显著提高, 从75.5(x = 0)提高到了108.9(x = 0.35). LNCM@Cr2O5复合正极材料和Li4Ti5O12负极材料匹配而成的新型锂离子全电池, 即LNCM@Cr2O5//Li4Ti5O12(L电池)表现出高达97.7的ICE. 不仅如此, L电池还表现出了高达250 mA h g—1的可逆容量, 并且 在循环50次之后仍具有94%的容量保持率. 此外, 在1.25和2.5 A g—1电流密度下, 它还具有高达122和94 mA h g—1的放电比容量, 远远优于LNCM//石墨全电池(G电池). L电池的高性能得益于精心设计的库仑效率匹配机制, 并且在未来高能量锂离子电池的快速充放电应用中表现出巨大的潜力.