Carbon Nanotube@RuO2 as a High Performance Catalyst for Li-CO2 Batteries.

Efficient electrocatalysts for Li2CO3 decomposition play an important role in Li-CO2 batteries. In this paper, carbon nanotubes (CNTs) decorated with RuO2 is firstly introduced as cathode materials for Li-CO2 batteries. The CNT@RuO2 composite can not only deliver a high specific capacity but also a lower charge voltage. With the CNT@RuO2 cathodes, the Coulombic efficiency still remains around 100% until the 15th cycle. The charge voltage of early 30 cycles at a current of 50 mA·g-1 with a capacity limit of 500 mAh·g-1 can be fully lowered under 4.0 V. Particularly, the CNT@RuO2 cathode can realize most decomposition of prefilled Li2CO3 and show a platform at around 3.9 V. This catalytic activity toward both in situ formed and preloaded Li2CO3 is more feasible for practical application in complex environment.

An ultrathin surface-nitrided porous titanium sheet as a current collector-free sulfur host for high-gravimetric-capacity lithium-sulfur batteries.

A novel cathode structure consisting of ultrathin and freestanding surface-nitrided porous titanium (SNPT) sheets, was designed for high-gravimetric-capacity Li-S batteries. This unusual cathode combines the sulfur host and the current collector together, increasing the sulfur mass ratio by over 20% compared with routine cathodes, resulting in excellent cycling performance with an initial capacity of 1325 mA h g-1 and a coulombic efficiency of over 99% at 1.0C.

Coprecipitation-Gel Synthesis and Degradation Mechanism of Octahedral Li1.2Mn0.54Ni0.13Co0.13O2 as High-Performance Cathode Materials for Lithium-Ion Batteries.

The octahedral core-shell Li-rich layered cathode material of Li1.2Mn0.54Ni0.13Co0.13O2 can be synthesized via an ingenious coprecipitation-gel method without subsequent annealing. On the basis of detailed X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy characterizations, it is suggested that the as-prepared material consists of an octahedral morphology and a new type of core-shell structure with a spinel-layered heterostructure inside, which is the result of overgrowth of the spinel structure with {111} facets on {001} facets of the layered structure in a single orientation. The surface area of Li1.2Mn0.54Ni0.13Co0.13O2 crystals where the spinel phase is located possesses sufficient Li and O vacancies, resulting in the reinsertion of Li into position after the first charge and maintenance of the interface stability via the replenishment of oxygen from the bulk region. Compared to that synthesized by the traditional coprecipitation method, the Li1.2Mn0.54Ni0.13Co0.13O2 synthesized by the coprecipitation-gel method exhibits higher discharge capacity and Coulombic efficiency, from 73.9% and 251.5 mAh g-1 for the spherical polycrystal material to 86.2% and 291.4 mAh g-1.

Effect of Defects on Decay of Voltage and Capacity for Li[Li0.15Ni0.2Mn0.6]O2 Cathode Material.

Lithium-rich manganese metal layered oxides are very promising cathode materials for high-energy-density lithium-ion batteries, but improvement in voltage decay and capacity fade is a great challenge, which is mainly related to the structural instability or reconstruction of material's surface. Defects, such as part lattice distortions, local cation disordering and atomic ununiformity, often aggravate the further structural changes upon cycling. In this paper, we found that PEG contributed to form better layered structure, well crystallinity, uniform composition and polyhedral nanoparticles for Li[Li0.15Ni0.2Mn0.6]O2 (LNMO). On the basis of the comparative trial, a mechanism of electronegativity difference is proposed to elucidate cation nonuniform distribution. Higher electronegativity of Ni (1.91) than Mn (1.55) show a stronger ability of attraction between Ni and O atoms, and then led to Ni atoms show stronger diffusion driving force toward particle surface to contact the rich O atoms during sintering in air. However, PEG polymer can form a better barrier for more O atoms to attract Ni and Mn atoms on particle surface so that facilitated a uniform distribution. The electrochemical test indicated that the decay of discharge capacity and working voltage was mitigated, which was identified by the result of HRTEM analysis that the initial less defect structure obviously retarded the phase transformation from the layered to spinel after 50 cycles. Therefore, defects are crucial for understanding the voltage fade and capacity decay, and the improvement of performance also demonstrates that designing optimum compositions and ordering atomic arrangements will contribute to stabilize the surface structure and restrain inherent phase transitions.