Liqiang Mai

Electrospun Ultralong Hierarchical Vanadium Oxide Nanowires with High Performance for Lithium Ion Batteries

Ultralong hierarchical vanadium oxide nanowires with diameter of 100-200 nm and length up to several millimeters were synthesized using the low-cost starting materials by electrospinning combined with annealing. The hierarchical nanowires were constructed from attached vanadium oxide nanorods of diameter around 50 nm and length of 100 nm. The initial and 50th discharge capacities of the ultralong hierarchical vanadium oxide nanowire cathodes are up to 390 and 201 mAh/g when the lithium ion battery cycled between 1.75 and 4.0 V. When the battery was cycled between 2.0 and 4.0 V, the initial and 50th discharge capacities of the nanowire cathodes are 275 and 187 mAh/g. Compared with self-aggregated short nanorods synthesized by hydrothermal method, the ultralong hierarchical vanadium oxide nanowires exhibit much higher capacity. This is due to the fact that self-aggregation of the unique nanorod-in-nanowire structures have been greatly reduced because of the attachment of nanorods in the ultralong nanowires, which can keep the effective contact areas of active materials, conductive additives, and electrolyte large and fully realize the advantage of nanomaterial-based cathodes. This demonstrates that ultralong hierarchical vanadium oxide nanowire is one of the most favorable nanostructures as cathodes for improving cycling performance of lithium ion batteries.

Na+ intercalation pseudocapacitance in graphene-coupled titanium oxide enabling ultra-fast sodium storage and long-term cycling

Sodium-ion batteries are emerging as a highly promising technology for large-scale energy storage applications. However, it remains a significant challenge to develop an anode with superior long-term cycling stability and high-rate capability. Here we demonstrate that the Na(+) intercalation pseudocapacitance in TiO2/graphene nanocomposites enables high-rate capability and long cycle life in a sodium-ion battery. This hybrid electrode exhibits a specific capacity of above 90 mA h g(-1) at 12,000 mA g(-1) (∼36 C). The capacity is highly reversible for more than 4,000 cycles, the longest demonstrated cyclability to date. First-principle calculations demonstrate that the intimate integration of graphene with TiO2 reduces the diffusion energy barrier, thus enhancing the Na(+) intercalation pseudocapacitive process. The Na-ion intercalation pseudocapacitance enabled by tailor-deigned nanostructures represents a promising strategy for developing electrode materials with high power density and long cycle life.

Nanowire electrodes for electrochemical energy storage devices.

Liqiang Mai,*,† Xiaocong Tian,† Xu Xu,† Liang Chang,‡ and Lin Xu†,§ †State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, WUT-Harvard Joint Nano Key Laboratory, Wuhan University of Technology, Wuhan 430070, China ‡Department of Materials Science and Engineering, Michigan Technological University, Houghton, Michigan 49931-1295, United States Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States

Effect of Carbon Matrix Dimensions on the Electrochemical Properties of Na3V2(PO4)3 Nanograins for High‐Performance Symmetric Sodium‐Ion Batteries

Na3V2(PO4)3 nanograins dispersed in different carbon matrices are rationally synthesized and systematically characterized. The acetylene carbon matrix provides the best conductive networks for electrons and sodium ions, which endows Na3V2(PO4)3 stable cyclability and high rate performance. The Na3V2 (PO4)3 -based symmetric sodium-ion batteries show outstanding electrochemical performance, which is promising for large-scale and low-cost energy storage applications.

Synergistic interaction between redox-active electrolyte and binder-free functionalized carbon for ultrahigh supercapacitor performance

Development of supercapacitors with high-energy density and high-power density is a tremendous challenge. Although the use of conductive carbon materials is promising, other methods are needed to reach high cyclability, which cannot be achieved by fully utilizing the surface-oxygen redox reactions of carbon. Here we introduce an effective strategy that utilizes Cu(2+) reduction with carbon-oxygen surface groups of the binder-free electrode in a new redox-active electrolyte. We report a 10-fold increase in the voltammetric capacitance (4,700 F g(-1)) compared with conventional electrolyte. We measured galvanostatic capacitances of 1,335 F g(-1) with a retention of 99.4% after 5,000 cycles at 60 A g(-1) in a three-electrode cell and 1,010 F g(-1) in a two-electrode cell. This improvement is attributed to the synergistic effects between surface-oxygen molecules and electrolyte ions as well as the low charge transfer resistance (0.04 Ω) of the binder-free porous electrode. Our strategy provides a versatile method for designing new energy storage devices and is promising for the development of high-performance supercapacitors for large-scale applications.

Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries

Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g –1, one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire.

Manganese Oxide/Carbon Yolk−Shell Nanorod Anodes for High Capacity Lithium Batteries

Transition metal oxides have attracted much interest for their high energy density in lithium batteries. However, the fast capacity fading and the low power density still limit their practical implementation. In order to overcome these challenges, one-dimensional yolk-shell nanorods have been successfully constructed using manganese oxide as an example through a facile two-step sol-gel coating method. Dopamine and tetraethoxysilane are used as precursors to obtain uniform polymer coating and silica layer followed by converting into carbon shell and hollow space, respectively. As anode material for lithium batteries, the manganese oxide/carbon yolk-shell nanorod electrode has a reversible capacity of 660 mAh/g for initial cycle at 100 mA/g and exhibits excellent cyclability with a capacity of 634 mAh/g after 900 cycles at a current density of 500 mA/g. An enhanced capacity is observed during the long-term cycling process, which may be attributed to the structural integrity, the stability of solid electrolyte interphase layer, and the electrochemical actuation of the yolk-shell nanorod structure. The results demonstrate that the manganese oxide is well utilized with the one-dimensional yolk-shell structure, which represents an efficient way to realize excellent performance for practical applications.

Nanostructured Metal Oxides and Sulfides for Lithium–Sulfur Batteries

Lithium-sulfur (Li-S) batteries with high energy density and long cycle life are considered to be one of the most promising next-generation energy-storage systems beyond routine lithium-ion batteries. Various approaches have been proposed to break down technical barriers in Li-S battery systems. The use of nanostructured metal oxides and sulfides for high sulfur utilization and long life span of Li-S batteries is reviewed here. The relationships between the intrinsic properties of metal oxide/sulfide hosts and electrochemical performances of Li-S batteries are discussed. Nanostructured metal oxides/sulfides hosts used in solid sulfur cathodes, separators/interlayers, lithium-metal-anode protection, and lithium polysulfides batteries are discussed respectively. Prospects for the future developments of Li-S batteries with nanostructured metal oxides/sulfides are also discussed.

One-Pot Synthesized Bicontinuous Hierarchical Li3V2(PO4)3/C Mesoporous Nanowires for High-Rate and Ultralong-Life Lithium-ion Batteries

Lithium-ion batteries have attracted enormous attention for large-scale and sustainable energy storage applications. Here we present a design of hierarchical Li3V2(PO4)3/C mesoporous nanowires via one-pot synthesis process. The mesoporous structure is directly in situ carbonized from the surfactants (CTAB and oxalic acid) along with the crystallization of Li3V2(PO4)3 without using any hard templates. As a cathode for lithium-ion battery, the Li3V2(PO4)3/C mesoporous nanowires exhibit outstanding high-rate and ultralong-life performance with capacity retention of 80.0% after 3000 cycles at 5 C in 3-4.3 V. Even at 10 C, it still delivers 88.0% of its theoretical capacity. The ability to provide this level of performance is attributed to the hierarchical mesoporous nanowires with bicontinuous electron/ion pathways, large electrode-electrolyte contact area, low charge transfer resistance, and robust structure stability upon prolonged cycling. Our work demonstrates that the unique mesoporous nanowires structure is favorable for improving the cyclability and rate capability in energy storage applications.

SnO2 Quantum Dots@Graphene Oxide as a High‐Rate and Long‐Life Anode Material for Lithium‐Ion Batteries

Tin-based electrode s offer high theoretical capacities in lithium ion batteries, but further commercialization is strongly hindered by the poor cycling stability. An in situ reduction method is developed to synthesize SnO2 quantum dots@graphene oxide. This approach is achieved by the oxidation of Sn(2+) and the reduction of the graphene oxide. At 2 A g(-1), a capacity retention of 86% is obtained even after 2000 cycles.