No abstract

Operation of the nonaqueous Li–O2 battery critically relies on the reversible oxygen reduction/evolution reactions in the porous cathode. Carbon and polymeric binder, widely used for the construction of Li–O2 cathode, have recently been shown to decompose in the O2 environment and thus cannot sustain the desired battery reactions. Identifying stable cathode materials is thus a major current challenge that has motivated extensive search for noncarbonaceous alternatives. Here, RuOx/titanium nitride nanotube arrays (RuOx/TiN NTA) containing neither carbon nor binder are used as the cathode for nonaqueous Li–O2 batteries. The free standing TiN NTA electrode is more stable than carbon electrode, and possesses enhanced electronic conductivity compared to TiN nanoparticle bound with polytetrafluoroethylene due to a direct contact between TiN and Ti mesh substrate. RuOx is electrodeposited into TiN NTA to form a coaxial nanostructure, which can further promote the oxygen evolution reaction. This optimized monolithic electrode can avoid the side reaction arising from carbon material, which exhibits low overpotential and excellent cycle stability over 300 cycles. These results presented here demonstrate a highly effective carbon‐free cathode and further imply that the structure designing of cathode plays a critical role for improving the electrochemical performance of nonaqueous Li–O2 batteries.

The electrochemical performance of lithium-oxygen (Li-O 2 ) batteries can be markedly improved through designing the architecture of cathode electrodes with sufficient spaces to facilitate the diffusion of oxygen and accommodate the discharge products, and optimizing the cathode catalyst to promote the oxygen reduction reaction and oxygen evolution reaction (OER). Herein, we report the synthesis of ruthenium (Ru) nanocrystal-decorated vertically aligned graphene nanosheets (VGNS) grown on nickel (Ni) foam. As an effective binder-free cathode catalyst for Li-O 2 batteries, the Ru-decorated VGNS@Ni foam can significantly reduce the charge overpotential via the effects on the OER and achieve high specific capacity, leading to an enhanced electrochemical performance. The Ru-decorated VGNS@Ni foam electrode has demonstrated low charge overpotential of~0.45 V and high reversible capacity of 23 864 mAh g − 1 at the current density of 200 mA g − 1 , which can be maintained for 50 cycles under full charge and discharge testing condition in the voltage range of 2.0-4.2 V. Furthermore, Ru nanocrystal decorated VGNS@Ni foam can be cycled for more than 200 cycles with a low overpotential of 0.23 V under the capacity curtained to be 1000 mAh g − 1 at a current density of 200 mA g − 1 . Ru-decorated VGNS@Ni foam electrodes have also achieved excellent high rate and long cyclability performance. This superior electrochemical performance should be ascribed to the unique three-dimensional porous nanoarchitecture of the VGNS@Ni foam electrodes, which provide sufficient pores for the diffusion of oxygen and storage of the discharge product (Li 2 O 2 ), and the effective catalytic effect of Ru nanocrystals on the OER, respectively. Ex situ field emission scanning electron microscopy, X-ray diffraction, Raman and Fourier transform infrared measurements revealed that Ru-decorated VGNS@Ni foam can effectively decompose the discharge product Li 2 O 2 , facilitate the OER and lead to a high round-trip efficiency. Therefore, Ru-decorated VGNS@Ni foam is a promising cathode catalyst for rechargeable Li-O 2 batteries with low charge overpotential, long cycle life and high specific capacity.

No abstract

Silicon (Si) has been used in Li-ion batteries (LIBs), and considerable progress has been achieved in design and engineering with improved capacity and cycling.

The reaction kinetics of electrochemical lithiation/delithiation in a composite consisting of black phosphorus and cup-stacked carbon nanotube (BP-CSCNT) were investigated. Two semicircles were observed in Nyquist plots at the high and low frequency regions, which were attributed to the resistance of lithium-ion transport through the surface film and the resistance of the alloying/dealloying reaction (charge-transfer resistance), respectively. The activation energy using the charge transfer reaction was evaluated from the temperature-dependence of the interfacial conductivity. Even with the use of ethylene carbonate-based and propylene carbonate electrolytes, the activation energy was calculated to be 25-26 kJ mol −1 , which is much smaller than that obtained with graphite electrodes and cathode materials. These results indicate that the ionic charge transfer process in BP-CSCNT composite electrodes is not coupled with the desolvation process and suggest that the charge transfer in BP-CSCNT is exceptionally fast compared to that in other insertion materials.