The Synergistic Effect of MoS2 and NiS on the Electrical Properties of Iron Anodes for Ni-Fe Batteries.

In this paper, a series of Fe3O4/MoS2/NiS composite electrodes were synthesized by a simple coprecipitation method. The influence of different ratio additives (MoS2 and NiS) on the performance of iron anodes for Ni-Fe batteries was systematically investigated. In this paper, the mixed alkaline solution of 6 mol/L NaOH and 0.6 mol/L LiOH was used as electrolyte, and sintered Ni(OH)2 was used as counterelectrode. The experimental results show that the MoS2 and NiS additives can effectively eliminate the passivation phenomena in iron electrodes, reduce the electrode polarization, and increase the reversibility capacity. As a result, the Fe3O4/MoS2/NiS composite electrodes exhibit a high specific capacity, good rate performance, and long cycling stability. Especially, the Fe3O4/MoS2 (5%)/NiS (5%) electrode with a suitable ratio of additives can provide excellent electrochemical performance, with high discharge capacities of 657.9 mAh g-1, 639.8 mAh g-1, and 442.1 mAh g-1 at 600 mA g-1, 1200 mA g-1, and 2400 mA g-1, respectively. This electrode also exhibits good cycling stability.

Powder exfoliated MoS2 nanosheets with highly monolayer-rich structures as high-performance lithium-/sodium-ion-battery electrodes.

Due to their low yield and easy aggregation during the electrode preparation process, exfoliated MoS2 monolayers cannot fulfill the requirements of alkali-metal-ion battery tests. Hence, we have developed a facile process to fabricate powder exfoliated MoS2 nanosheets capable of large-scale production and having highly monolayer-rich structures. This process contains two steps: liquid-phase exfoliation of the edge-rich MoS2 precursor and a freeze-drying procedure. The proposed MoS2 precursors contain rich edge fractions that are easily exfoliated by this method, and the freeze-drying procedure can maintain the unique monolayer-rich structure of MoS2 in the powder phase. The electrochemical evaluations of both lithium- and sodium-ion batteries reveal that the proposed powder exfoliated monolayer-rich MoS2 electrode exhibits remarkable specific capacities and stable cyclic performances. In particular, the monolayer-rich MoS2 nanosheet electrode delivers a superior lithium-storage capacity of ∼1400 mA h g-1. The exfoliated MoS2 nanosheet electrode can withstand over 1000 cycles even at 1 A g-1. The mechanism reveals that these unique MoS2 nanosheets not only have a large surface area but also their inclusive monolayer structures exhibit much higher charge mobility than those of bulk MoS2.

In situ synthesis of open hollow tubular MnO/C with high performance anode materials for lithium ion batteries using kapok fiber as carbon matrix.

MnO/C materials with a long lifetime and high rate performance via a biomass template strategy for the lithium ion battery (LIB) market are indispensable. Therefore, novel and efficient ways for their synthesis are urgently required to greatly alleviate the pressure of consuming nonrenewable resources. Herein, we fabricate an open hollow tubular MnO/C hybrid based on the transformation of a natural kapok fiber by hydrothermal and thermal treatment. The as-prepared hybrid material was obtained with high synthesis efficiency and exhibited an extremely stable structure attributed to the in situ growth strategy, overcoming volumetric expansion and self-aggregation of MnO. As an anode material for LIBs, this typical MnO/C electrode demonstrated a high reversible capacity of 1917 mAh · g-1 at 300 mA · g-1 and an excellent rate performance of 693.1 mAh · g-1 at 5000 mA · g-1. More importantly, this biomass carbon-based material demonstrates a superior cycling stability of 1433.1 mAh · g-1 at a high current density of 5000 mA · g-1 after 1000 cycles. The significant electrical performance of this new type of green material is promising for the development of LIBs.

Facile and Nonradiation Pretreated Membrane as a High Conductive Separator for Li-Ion Batteries.

Polyolefin membranes are widely used as separators in commercialized Li-ion batteries. They have less polarized surfaces compared with polarized molecules of electrolyte, leading to a poor wetting state for separators. Radiation pretreatments are often adopted to solve such a problem. Unfortunately, they can only activate several nanometers deep from the surface, which limits the performance improvement. Here we report a facile and scalable method to polarize polyolefin membranes via a chemical oxidation route. On the surfaces of pretreated membrane, layers of poly(ethylene oxide) and poly(acrylic acid) can easily be coated, thus resulting in a high Li-ion conductivity of the membrane. Assembled with this decorated separator in button cells, both high-voltage (Li1.2Mn0.54Co0.13Ni0.13O2) and moderate-voltage (LiFePO4) cathode materials show better electrochemical performances than those assembled with pristine polyolefin separators.

Solvent dynamics effect in condensed-phase electron-transfer reactions.

Channel-based reaction-diffusion equations are solved analytically for two electron transfer (ET) models, where the fast inner-sphere coordinate leads to an ET reaction treated by Fermi's golden rule, and the slow solvent coordinate moves via diffusion. The analytic solution has let us derive an ET rate constant that modifies the Marcus-Jortner formula by adding a constant alpha which we call a dynamic correction factor. The dynamic correction factor measures the effect of solvent friction. When the relaxation of solvent dynamics is fast, the dynamic correction can be neglected and the ET rate constant reduces to the traditional Marcus-Jortner formula. If the solvent dynamic relaxation is slow, the dynamic correction can be very large and the ET rate can be reduced by orders of magnitude. Using a generalized Zusman-Sumi-Marcus model as a starting point, we introduce two variants, GZSM-A and GZSM-B, where in model A, only one quantum mode is considered for inner-sphere motion and in model B, a classical mode for inner-sphere motion is added. By comparing the two models with experimental data, it is shown that model B is better than model A. For the solvents that have a relaxation time ranging between 0 and 5 ps, our result agrees fairly well with experimental data; for the solvents that have a relaxation time ranging between 5 and 40 ps, our result deviates from the experimental values. After introducing an adjustable scaling index in the effective time correlation function of the reaction coordinate, good agreement is achieved between the experiment and the theory for model B for all of the solvents studied in this paper.