Sanpei Zhang

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.

Graphene nanosheets loaded with Pt nanoparticles with enhanced electrochemical performance for sodium-oxygen batteries

Graphene nanosheets loaded with highly dispersed platinum nanoparticles (Pt@GNSs) are prepared by a simple and effective hydrothermal method. The Pt@GNS as an air cathode material exhibits a very high initial discharge capacity of 7574 mA h−1 g−1 at a current density of 0.1 mA cm−2 and delivers a stable cycling performance. The electrocatalytic characteristics of Pt on the Na–O2 cell have been investigated for the first time.

Sulfonic Groups Originated Dual-Functional Interlayer for High Performance Lithium–Sulfur Battery

The lithium-sulfur battery is one of the most prospective chemistries in secondary energy storage field due to its high energy density and high theoretical capacity. However, the dissolution of polysulfides in liquid electrolytes causes the shuttle effect, and the rapid decay of lithium sulfur battery has greatly hindered its practical application. Herein, combination of sulfonated reduced graphene oxide (SRGO) interlayer on the separator is adopted to suppress the shuttle effect. We speculate that this SRGO layer plays two roles: physically blocking the migration of polysulfide as ion selective layer and anchoring lithium polysulfide by the electronegative sulfonic group. Lewis acid-base theory and density functional theory (DFT) calculations indicate that sulfonic groups have a strong tendency to interact with lithium ions in the lithium polysulfide. Hence, the synergic effect involved by the sulfonic group contributes to the enhancement of the battery performance. Furthermore, the uniformly distributed sulfonic groups working as active sites which could induce the uniform distribution of sulfur, alleviating the excessive growth of sulfur and enhancing the utilization of active sulfur. With this interlayer, the prototype battery exhibits a high reversible discharge capacity of more than 1300 mAh g-1 and good capacity retention of 802 mAh g-1 after 250 cycles at 0.5 C rate. After 60 cycles at different rates from 0.2 to 4 C, the cell with this functional separator still recovered a high specific capacity of 1100 mAh g-1 at 0.2 C. The results demonstrate a promising interlayer design toward high performance lithium-sulfur battery with longer cycling life, high specific capacity, and rate capability.

A rGO–CNT aerogel covalently bonded with a nitrogen-rich polymer as a polysulfide adsorptive cathode for high sulfur loading lithium sulfur batteries

The development of high capacity lithium–sulfur (Li–S) batteries is hampered by both the shuttle effect of polysulfides and low sulfur areal loading problems. To inhibit the shuttle effect, a polysulfide adsorptive polymer polyethylenimine (PEI) is covalently bonded with reduced graphene oxide (rGO) in a one-step hydrothermal reaction. Meanwhile, multi-walled carbon nanotubes (MWCNTs) are simultaneously interweaved with rGO. The resultant PEI–rGO–MWCNT aerogel (PEI–GC) provides ample chemisorption domains of amine groups and abundant electrical contact sites. Density functional theory (DFT) calculations prove a binding energy of 2.43 eV between PEI and polysulfide. The PEI–GC cell achieved a high capacity of 933 mA h g−1 for the 500th cycle at 1C, stable rate performance up to 10C, and low self-discharge rate. The covalent bond between PEI and rGO experiences no degradation during the 500 cycles. Moreover, PEI–GC achieved excellent cycling performance at a high sulfur loading of up to 18 mg cm−2.

Suppressing the dissolution of polysulfides with cosolvent fluorinated diether towards high-performance lithium sulfur batteries.

The dissolution and shuttle of polysulfides in electrolytes cause severe anode corrosion, low coulombic efficiency, and a rapid fading of the capacity of lithium-sulfur batteries. Fluorinated diether (FDE) was selected as a cosolvent in traditional ether electrolytes to suppress the dissolution of polysulfides. The modified electrolytes lead to a negligible solubility of polysulfides, as well as decreased corrosion of the lithium anode. In an optimal system, the cells show improved cycling performance with an average coulombic efficiency of above 99% and a highly stable reversible discharge capacity of 701 mA h g-1 after 200 cycles at a 0.5C rate. A combination of electrochemical studies and X-ray photoelectron spectroscopy demonstrates the sulfur reduction mechanism with three voltage plateaus.

Local Lattice Distortion Activate Metastable Metal Sulfide as Catalyst with Stable Full Discharge–Charge Capability for Li–O2 Batteries

The direct lattice strain, either distortion, compressive, or tensile, can efficiently alter the intrinsic electrocatalytic property of the catalysts. In this work, we report a novel and effective strategy to distort the lattice structure by constructing a metastable MoSSe solid solution and thus, tune its catalytic activity for the Li-O2 batteries. The lattice distortion structure with inequivalent interplanar spacing between the same crystals plane were directly observed in individual MoSSe nanosheets with transmission electron microscopy and aberration-corrected transmission electron microscopy. In addition, in situ transmission electron microscopy analysis revealed the fast Li+ diffusion across the whole metastable structure. As expected, when evaluated as oxygen electrode for deep-cycle Li-O2 batteries, the metastable MoSSe solid solution deliver a high specific capacity of ∼730 mA h g-1 with stable discharge-charge overpotentials (0.17/0.49 V) over 30 cycles.

Controlling uniform deposition of discharge products at the nanoscale for rechargeable Na–O2 batteries

Sodium–oxygen batteries are an attractive alternative for electrical energy storage applications because of their high-energy density and low cost. As a common challenge for all air-based battery systems, Na–O2 batteries also suffer from inefficient reversible formation of discharge products and poor cycling performance. Here, we report the design and synthesis of a binder-free air electrode composed of three-dimensional (3D) nitrogen-doped graphene aerogels (N-GAs). In this design, nitrogen-doped graphene aerogels grow directly on the Ni foam (3D N-GA@Ni) with a well-preserved interconnected 3D architecture. The Na–O2 cell with the 3D N-GA electrode is capable of large capacity (10 905 mA h gcarbon−1 at a current density of 100 mA gcarbon−1), long cycle life (over 100 cycles at 100 mA g−1 with a specific capacity limit of 500 mA h gcarbon−1) and high rate performance (over 50 cycles at 300 mA gcarbon−1). These properties are mainly attributed to the active N-group, which controls the uniform deposition of discharge products at the nanoscale and provides active sites for decreasing overpotential. This encouraging performance also offers a brand new approach to improve the electrochemical performance of Na–O2 batteries and other metal–air batteries.

Highly active mixed-valent MnOx spheres constructed by nanocrystals as efficient catalysts for long-cycle Li–O2 batteries

Developing highly active and cost-effective catalysts for Li–O2 batteries with high capacity, long cycle life and good rate performance is still challenging. In this work, a simple and efficient strategy is developed for the synthesis of MnOx spheres with a core–multishell structure. The spheres are assembled by ultrafine manganese oxide nanocrystals containing mixed-valent MnII, MnIII, and MnIV species. The Li–O2 batteries with MnOx sphere electrodes can deliver high discharge capacity, long-life cycling and excellent rate performance, namely, a specific capacity as large as 9709 mA h gcarbon−1 is delivered at 100 mA gcarbon−1 and maintained over 320 cycles at a limited capacity of 1000 mA h gcarbon−1. Even at a high capacity (2000 mA h gcarbon−1) with a high current density of 200 mA gcarbon−1, the batteries can still endure more than 120 cycles. During the long cycling, the batteries show ultra-stable electrochemical performance with a high discharge potential (2.8–2.9 V) and low charge voltage (3.7–3.8 V). High-resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy analyses for cycled mixed-valent MnOx electrodes are used to reveal the electrochemical mechanism.

Assembly of Multifunctional Ni2P/NiS0.66 Heterostructures and Their Superstructure for High Lithium and Sodium Anodic Performance

The combination of structure designs at the microscopic and macroscopic level can efficiently enable electrode materials with greatly enhanced lithium and sodium storage. In this paper, the construction of Ni2P/NiS0.66 heterostructures and their assembly into a superstructure at the nanoscale were successfully achieved by a facile and effective strategy. In the obtained superstructure, the Ni2P/NiS0.66 heterostructures are homogeneously coated with ultrathin carbon layers (HT-NPS@C) and, at the same time, assembled into a yolk-shell nanosphere. Upon evaluation as the anode materials for Li-ion batteries, the HT-NPS@C delivers a high reversible capacity of 430 mA h g-1 after 200 cycles at 200 mA g-1 and ultrastable cyclability with negligible capacity loss over 500 cycles. Furthermore, the coin-type full cell with the LiNi1/3Co1/3Mn1/3O2 (LNCMO) cathode and HT-NPS@C anode deliver a high specific capacity of 323.5 mA h g-1 after 50 cycles at 0.3 A g-1. Apart from an excellent performance as promising anode materials for LIBs (Li-ion batteries), the Na-ion batteries with HT-NPS@C sphere electrodes also manifest a remarkable electrochemical performance.

Influence of Cu2+ doping concentration on the catalytic activity of CuxCo3−xO4 for rechargeable Li–O2 batteries

The electrochemical performance of rechargeable lithium–oxygen (Li–O2) batteries relies on the catalysts used in the cathode to a great extent. Herein, a series of CuxCo3−xO4 nanorods with different Cu2+ concentrations was prepared by a convenient hydrothermal method. The corresponding structures and electrochemistries were further characterized in order to reveal the composition effect of catalyst on catalytic activity. Experimental characterization and theoretical calculations indicate that more Cu2+ occupying Co2+ positions and dispersing on the catalyst surface has an enhanced catalytic activity in terms of higher capacity, lower overpotential and better reversibility. This implies that suitable charge transfer from Li2O2 to the catalyst plays an important role in improving the electrochemical performance of Li–O2 batteries. The present study is helpful for designing a highly active catalyst by tuning the composition of the catalyst surface.