S.H. Ye

Surface nitridation of Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide as cathode material for lithium-ion battery

A Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide is prepared by a combination of co-precipitation and solid-state reaction. The surface nitridation is introduced into a Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 for the first time via heating at 400 °C in the ammonia atmosphere. The microstructure and morphology of the two samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is demonstrated that the nitrogen exists with a trace amount in the surface layer of the Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide after the nitridation treatment. Electrochemical performances of the electrodes are measured by galvanostatic charge–discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). As expected, the discharge capacity, high-rate capability and cycle stability of the nitrided sample are improved dramatically as compared with the as-prepared sample, which is further confirmed by the high electrocatalytic activity and accelerated lithium diffusion process. Apparently, the existence of nitrogen in the surface layer is responsible for the improvement of the reaction kinetics and electrochemical performance of the nitrided sample.

Surface modification of Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide with Li–Mn–PO4 as the cathode for lithium-ion batteries

Enhancement of the discharge capacity, high-rate capability, and cycle stability of the Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide with a large specific capacity is highly significant for high energy lithium-ion batteries. In this work, the Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide is prepared by a spray-drying method. The surface modification with the Li–Mn–PO4 is introduced onto Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide for the first time. It is demonstrated that the surface of Li(Li0.17Ni0.25Mn0.58)O2 grains is coated with the thin amorphous Li–Mn–PO4 layer (5 wt%). With increasing calcination temperature after the surface coating, a strong interaction can be induced on the interface between the amorphous Li–Mn–PO4 layer and the top surface of Li(Li0.17Ni0.25Mn0.58)O2 grains. As anticipated, the discharge capacity and high-rate capability are obviously improved for the Li–Mn–PO4-coated sample after calcination at 400 °C, while excellent cycle stability is obtained for the Li–Mn–PO4-coated sample after calcination at 500 °C as compared with the as-prepared Li(Li0.17Ni0.25Mn0.58)O2 oxide during cycling. Apparently, the interface interaction between the amorphous Li–Mn–PO4 layer and the top surface of Li(Li0.17Ni0.25Mn0.58)O2 grains is responsible for the improvement of the reaction kinetics and the electrochemical cycle stability of Li–Mn–PO4-coated samples.

In situ sulfur deposition route to obtain sulfur–carbon composite cathodes for lithium–sulfur batteries

An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S–CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g−1 at the current density of 160 mA g−1, respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g−1 with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium–sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S–CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging–discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur–carbon composite cathodes for rechargeable lithium–sulfur batteries.

Rechargeable lithium/iodine battery with superior high-rate capability by using iodine–carbon composite as cathode

A rechargeable lithium/iodine battery using commercial organic electrolyte, composed of iodine–conductive carbon black composite as cathode and metallic lithium as anode, is first proposed in this work. The fabricated lithium/iodine battery presents superior high-rate capability and good reversibility based on the contributions from both the capacitive characteristics of conductive carbon black, and the redox capacity of active iodine in the composite.

Fixing of highly soluble Br2/Br− in porous carbon as a cathode material for rechargeable lithium ion batteries

LiBr, as a representative of highly soluble electrochemically active materials, is fixed in nanopores of conductive carbon black (CCB). The Li/LiBr–CCB battery exhibits excellent high-rate capability to avoid slow solid-phase diffusion of Li ions in traditional solid cathode materials. The success will broaden the range of alternative materials for cathodes in LIBs and make them capable of providing both high power density and energy density.

Electrochemical Reduction Mechanism of Fe(VI) at a Porous Pt Black Electrode

Recently, ferrate(VI) has been widely investigated as a cathode material in alkaline batteries. The cathodic reduction process of the ferrate electrode is very important in understanding the electrochemical mechanism as well as in utilizing ferrate as a battery material. In this work, the direct electrochemical reduction process of K 2 FeO 4 was investigated by linear sweep voltammetry (LSV), with a porous Pt black electrode in a 9 M KOH solution at 25°C. The cathodic reaction process of FeO 2― 4 is controlled by the diffusion process in a potential range from 0.20 to 0.53 V (vs Hg/HgO). Moreover, the totally irreversible cathodic reactions of FeO 2― 4 include a rate-controlling step with an electron-transfer number less than 3. Sampled-current voltammetry was also applied to investigate the reaction processes, and the plot exhibits two limited currents. The first one is a weak one-electron limited current, corresponding to the rate-controlling step analyzed by LSV; the other one is a two-electron current. They are both affected by the diffusion of FeO 2― 4 ions. Therefore, the electrochemical reduction mechanism of FeO 2― 4 in 9 M KOH can be inferred as an overall three-electron process with a one-electron transfer as the rate-controlling step, in which the intermediate state of Fe(V) is generated from ferrate(VI).