Zhaoyin Wen

A free-standing-type design for cathodes of rechargeable Li–O2 batteries

A novel free-standing type cathode of rechargeable Li–O2 battery composed of only Co3O4 catalyst and Ni foam current collector was designed and realized by a simple chemical deposition reaction. The carbon and binder are no longer necessary for the air electrode. The new air electrode was found to yield obviously higher specific capacity and improved cycle efficiency than the conventional carbon-supported one with almost the highest discharge voltage (2.95 V), the lowest charge voltage (3.44 V), the highest specific capacity (4000 mAh g−1cathode) and the minimum capacity fading among the Li–O2 batteries reported to date. During its discharge process, the discharge products would deposit at the surface and in the pores of the free-standing catalysts. The improved performance was attributed to the abundant available catalytic sites of the particularly structured air electrode, the intimate contact of the discharge product with the catalyst, the effective suppression of the volume expansion in the electrode during subsequent deposition/decomposition of the discharge products, the good adhesion of the catalyst to the current collector, and the open pore system for unrestricted access of the reactant molecules to and from active sites of the catalysts. Furthermore, EIS study pointed out the intrinsic distinction resulting in the different performance between the new electrode and the conventional carbon-supported electrode. The new free-standing type electrode represents a critical step toward developing high-performance Li–O2 batteries.

Constructing Highly Oriented Configuration by Few-Layer MoS2: Toward High-Performance Lithium-Ion Batteries and Hydrogen Evolution Reactions.

Constructing three-dimensional (3D) architecture with oriented configurations by two-dimensional nanobuilding blocks is highly challenging but desirable for practical applications. The well-oriented open structure can facilitate storage and efficient transport of ion, electron, and mass for high-performance energy technologies. Using MoS2 as an example, we present a facile and effective hydrothermal method to synthesize 3D radially oriented MoS2 nanospheres. The nanosheets in the MoS2 nanospheres are found to have less than five layers with an expanded (002) plane, which facilitates storage and efficient transport of ion, electron, and mass. When evaluated as anode materials for rechargeable Li-ion batteries, the MoS2 nanospheres show an outstanding performance; namely, a specific capacity as large as 1009.2 mA h g(-1) is delivered at 500 mA g(-1) even after 500 deep charge/discharge cycles. Apart from promising the lithium-ion battery anode, this 3D radially oriented MoS2 nanospheres also show high activity and stability for the hydrogen evolution reaction.

A tubular polypyrrole based air electrode with improved O2 diffusivity for Li–O2 batteries

A highly reversible air electrode was designed based on the hydrophilic nano-PPy tubes with abundant gas diffusion channels and reaction space which greatly improved the cell capacity, cycling stability and especially the rate performance of the lithium–oxygen batteries.

Flexible self-supporting graphene–sulfur paper for lithium sulfur batteries

A flexible self-supporting graphene–sulfur paper with 67 wt% sulfur was fabricated for lithium sulfur batteries. This binder and current collector-free electrode demonstrated a reversible capacity of 600 mA h g−1 with 83% capacity retention based on the sulfur element after 100 cycles.

Enhanced cycle performance of a Li–S battery based on a protected lithium anode

A conductive polymer layer is prepared on the surface of a lithium anode as the protective layer for a Li–S battery. With the protective layer, a stable and less resistive SEI is formed between the ether-based electrolyte and the Li anode, it can not only inhibit the corrosion reaction between the lithium anode and lithium polysulfides effectively, but also suppress the growth of Li dendrites. Particularly, with approximately 2.5–3 mg cm−2 sulfur loading on the electrode and commercial electrolyte, the discharge capacity remains at 815 mA h g−1 after 300 cycles at 0.5 C with an average coulombic efficiency of 91.3%.

Hollow polyaniline sphere@sulfur composites for prolonged cycling stability of lithium–sulfur batteries

A sulfur cathode with excellent electrochemical performance has been designed based on hollow PANI spheres, which can suppress the shuttle effect and buffer the volume expansion effectively. The discharge capacity is as high as 602 mA h g−1 even after 1000 cycles at 0.5 C.

Preparation and Electrochemical Performance of Spinel-Type Compounds Li4Al y Ti5 − y O 12 ( y = 0 , 0.10, 0.15, 0.25)

Li 4 Ti 5 O 1 2 and Al 3 + doped Li 4 Al y Ti 5 - y O 1 2 (y = 0.10, 0.15, 0.25) were synthesized via solid-state reaction using TiO 2 -rutile, Li 2 CO 3 , and Al 2 O 3 as starting reagents. The charge-discharge cycling of the cells showed that the electrochemical performance of Li 4 Ti 5 O 1 2 prepared from rutile-type TiO 2 by our laboratory was as good as that produced by anatase-type TiO 2 . However, Al 3 + doped Li 4 Al y Ti 5 - y O 1 2 (y = 0.10, 0.15) exhibited a much better electrochemical performance in comparison with undoped Li 4 Ti 5 O 1 2 . Among the three samples of Li 4 Al y Ti 5 - y O 1 2 (y = 0, 0.10, 0.15), Li 4 Al 0 . 1 5 Ti 4 . 8 5 O 1 2 exhibited the largest reversible capacity and the highest coulombic efficiency. The discharge capacity values in the first and second cyclings were 195.6 and 173.6 mAh/g, respectively. The value remained 166.9 mAh/g after 30 cycles with a capacity loss of 3.86% compared to the second cycle, and the coulombic efficiency was 99.2% at the 30th cycle.

Surface Acidity as Descriptor of Catalytic Activity for Oxygen Evolution Reaction in Li-O2 Battery

Unraveling the descriptor of catalytic activity, which is related to physical properties of catalysts, is a major objective of catalysis research. In the present study, the first-principles calculations based on interfacial model were performed to study the oxygen evolution reaction mechanism of Li2O2 supported on active surfaces of transition-metal compounds (TMC: oxides, carbides, and nitrides). Our studies indicate that the O2 evolution and Li(+) desorption energies show linear and volcano relationships with surface acidity of catalysts, respectively. Therefore, the charging voltage and desorption energies of Li(+) and O2 over TMC could correlate with their corresponding surface acidity. It is found that certain materials with an appropriate surface acidity can achieve the high catalytic activity in reducing charging voltage and activation barrier of rate-determinant step. According to this correlation, CoO should have as active catalysis as Co3O4 in reducing charging overpotential, which is further confirmed by our comparative experimental studies. Co3O4, Mo2C, TiC, and TiN are predicted to have a relatively high catalytic activity, which is consistent with the previous experiments. The present study enables the rational design of catalysts with greater activity for charging reactions of Li-O2 battery.

Room-Temperature Mechanosynthesis of Ni3S2 as Cathode Material for Rechargeable Lithium Polymer Batteries

The formation of Ni 3 S 2 was realized by mechanical alloying with metallic nickel and sulfur powder as precursors. The products were characterized by X-ray diffraction, thermoanalysis, and scanning electron microscopy. Electrochemical properties of Li/P(EO) 20 Li(CF 3 SO 2 ) 2 N-10 wt % γ-LiAlO 2 /Ni 3 S 2 cells were also presented. The initial discharge capacity of Ni 3 S 2 was 304 mAh g -1 , with a platform at about 1.4 V vs Li/Li + . A capacity fading rate of 0.5% per cycle was achieved within 100 cycles. The charge-discharge mechanism of Ni 3 S 2 was implied by the analysis of the charge-discharge potential profiles, the cyclic voltammetry traces, and the ex situ XRD patterns of the Ni 3 S 2 cathode.

Effects of alumina whisker in (PEO)8–LiClO4-based composite polymer electrolytes

Abstract This paper reports the morphological, electrical and mechanical characteristics of the PEO-based composite polymer electrolytes with alumina whisker as fillers. The SEM results showed that serious microcracks occurred in the pristine PEO–LiClO 4 polymer electrolytes when they were quenched at room temperature and spherulites were allowed to form in the electrolytes. Addition of alumina whisker effectively prevented the formation of the microcracks. The whiskers were homogeneously dispersed in the polymer electrolyte matrix and exhibited excellent interconnection with PEO–LiClO 4 polymer electrolyte. The addition of whisker additives improved the ionic conductivity of the PEO–LiClO 4 polymer electrolytes to some extent when the content of the whisker was less than 20 wt.%. Moreover, the whisker could remarkably improve the mechanical performance of the PEO–LiClO 4 polymer electrolyte especially at the temperatures higher than its melting point.