Zhonghua Zhang

Nickel Disulfide–Graphene Nanosheets Composites with Improved Electrochemical Performance for Sodium Ion Battery

Nickel disulfide-graphene nanosheets (NiS2-GNS) composites were successfully synthesized via a simple and mild hydrothermal method. It was revealed by scanning electron microscopy and transmission electron microscopy images that the spherical NiS2 nanoparticles with a diameter of 200-300 nm were uniformly dispersed on graphene nanosheets. Na(+) electrochemical storage properties including cycling performance and high-rate capability of NiS2-GNS composites were investigated, demonstrating a superior reversible capacity of 407 mAh g(-1) with the capacity retention of 77% over 200 cycles at a current density of 0.1 C. Furthermore, even at a large current density of 2 C, a high capacity of 168 mAh g(-1) can still remain, which is much higher than that of pristine NiS2 materials. The enhancement in electrochemical properties might be attributed to the synergetic effect endowed by high conductivity of graphene and novel structure of the electrode material. Combined with the advantages of low cost and environmental benignity, NiS2-GNS composite would be a potential anode material for sodium ion batteries.

High energy density hybrid Mg2+/Li+ battery with superior ultra-low temperature performance

The development of high energy density rechargeable Mg-based batteries operating in a wide electrochemical window and ultra-low temperature remains a great challenge owing to parasitic side reactions between electrolytes and battery components when examined at high operating potentials (above 2.0 V vs. Mg2+/Mg). Herein we propose a flexible pyrolytic graphitic film (GF) as a reliable current collector of high-voltage cathodes for a hybrid Mg2+/Li+ battery within a pouch cell configuration. The utilization of such a highly electrochemical stable GF unlocks the critical bottleneck of incompatibility among all battery parts, especially parasitic corrosive reactions between electrolytes and currently available current collectors, which takes a big step forward towards the practical applications of Mg-based batteries. With an operating potential of 2.4 V, the hybrid Mg2+/Li+ battery designed by us can deliver a maximum energy density of 382.2 W h kg(-1), which significantly surpasses that of the conventional Mg battery (about 60 W h kg(-1)), and the Al battery (about 40 W h kg(-1)) as well as the state-of-the-art hybrid Na/Mg and Li/Mg batteries. The electrochemical property of the hybrid Mg2+/Li+ battery is also characterized by higher rate capability (68.8 mA h g(-1) at 3.0C), higher coulombic efficiency of 99.5%, and better cyclic stability (98% capacity retention after 200 cycles at 1.0C). In addition, the designed hybrid battery delivers excellent electrochemical performance at an ultra-low temperature of -40 degrees C, at which it retains 77% capacity compared to that of room temperature. Our strategy opens up a new possibility for widespread applications of graphitic current collectors towards high energy rechargeable Mg-based hybrid batteries, especially applied in polar regions, aerospace, and deep offshore waters.

Photosynthesis and growth responses of Parthenocissus quinquefolia (L.) Planch to soil water availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in PN and gs were not evident for the well-irrigated plants. With the lower water availability, midday reductions in PN and gs were much more marked and the duration of the depression was longer. Additionally, the PN-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.

An efficient organic magnesium borate-based electrolyte with non-nucleophilic characteristics for magnesium–sulfur battery

Two-electron transfer chemistry based on earth-abundant Mg and S offers great possibilities of delivering higher energy density than current Li-ion technology. The development of non-nucleophilic electrolytes that reversibly and efficiently plate and strip Mg is believed to be a major obstacle to the implementation of this divalent battery technology. In this study, we present a new type of organic magnesium borate-based electrolyte that primarily comprises tetrakis(hexafluoroisopropyl)borate anions [B(HFP)4]− and solvated cations [Mg4Cl6(DME)6]2+, which was synthesized via a facile in situ reaction of tris(hexafluoroisopropyl)borate [B(HFP)3], MgCl2 and Mg powder in 1,2-dimethoxyethane (DME). Rigorous analyses including NMR, mass spectroscopy and single-crystal XRD were conducted to identify the equilibrium species in the abovementioned solution. The as-prepared Mg-ion electrolyte exhibited unprecedented Mg plating/stripping performance, such as high anodic stability up to 3.3 V (vs. Mg/Mg2+), high ionic conductivity of 5.58 mS cm−1, a low overpotential of 0.11 V for plating processes and Coulombic efficiencies greater than 98%. By virtue of the non-nucleophilic nature of this electrolyte, a fully reversible Mg/S battery was constructed that displayed an extremely low overpotential of 0.3 V and a high discharge capacity of up to 1247 mA h g−1 and yielded a specific energy of approximately 1200 W h kg−1 (10 times higher that of the Chevrel benchmark) based on the weight of active sulfur. More significantly, commonly used sulfur-carbon nanotube (S-CNTs) cathodes with S contents of 80 wt% and S loadings of 1.5 mg cm−2 were demonstrated to withstand more than 100 cycles without obvious capacity decay and to enable fast conversion processes, which achieved a charging current rate of up to 500 mA g−1. Our findings convincingly validate the pivotal role of the newly designed non-nucleophilic Mg-ion electrolyte for practical Mg/S battery chemistry.

Li–O2 Cell with LiI(3-hydroxypropionitrile)2 as a Redox Mediator: Insight into the Working Mechanism of I– during Charge in Anhydrous Systems

Redox mediators (RMs) have been widely applied to reduce the charge overpotential of nonaqueous lithium-oxygen (Li-O2) batteries. Among the reported RMs, LiI is under hot debate with lots of controversial reports. However, there is a limited understanding of the charge mechanism of I- in anhydrous Li-O2 batteries. Here, we study the chemical reactivity between the oxidized state of I- and Li2O2. We confirm that the Li2O2 particles could be chemically oxidized by I2 rather than I3- species. Furthermore, our work demonstrates that the generated I- from Li2O2 oxidation would combine with I2 to give I3- species, hindering further oxidation of Li2O2 by I2. To improve the working efficiency of I- RMs, we introduce a compound LiI(3-hydroxypropionitrile)2 (LiI(HPN)2) with a high binding ability of I-. Compared with LiI, the cell that contained LiI(HPN)2 shows a significantly increased amount of I2 species during charge and enhanced Li2O2 oxidation efficiency under the same working conditions.

Graphene boosted Cu2GeS3 for advanced lithium-ion batteries

Germanium-based materials as the anode for lithium ion batteries (LIBs) have been investigated extensively because of their high theoretical capacities. However, ternary germanium-based sulfides as the anode material for LIBs have been rarely investigated until now. In this work, we successfully synthesized a novel ternary Cu2GeS3 (CGS) incorporated with reduced graphene oxide (CGS@RGO) and measured their lithium storage performance. As a result, the binder-free CGS@RGO anodes deliver excellent stable cycling properties and high rate capabilities. These improved properties can be ascribed to the introduction of RGO, which acts as a buffer to accommodate the large volume change and maintain the structural integrity of the electrode. More importantly, this work opens an opportunity to develop novel Ge-based anodes for high performance LIBs.

A Delicately Designed Sulfide Graphdiyne Compatible Cathode for High‐Performance Lithium/Magnesium–Sulfur Batteries

Novel sulfur cathodes hold the key to the development of metal-sulfur batteries, the promising candidate of next-generation high-energy-storage systems. Herein, a fascinating sulfur cathode based on sulfide graphdiyne (SGDY) is designed with a unique structure, which is composed of a conducting carbon skeleton with high Li+ mobility and short sulfur energy-storing unites. The SGDY cathode can essentially avoid polysulfide dissolution and be compatible with commercially available carbonate-based electrolytes and Grignard reagent-based electrolytes (all phenyl complex (APC) type electrolytes). Both the assembled Li-S and Mg-S batteries exhibit excellent electrochemical performances including large capacity, superior rate capability, high capacity retention, and high Coulombic efficiency. More importantly, this is the first implementation case of a reliable Mg-S system based on nucleophilic APC electrolytes.

Multifunctional Additives Improve the Electrolyte Properties of Magnesium Borohydride Toward Magnesium–Sulfur Batteries

Highly reductive magnesium borohydride [Mg(BH4)2] is compatible with metallic Mg, making it a promising Mg-ion electrolyte for rechargeable Mg batteries. However, pure Mg(BH4)2 in ether-based solutions displays very limited solubility (0.01 M), low oxidative stability (<1.8 V vs Mg), and nucleophilic characteristic, all of which preclude its practical utilization for any battery applications. Herein, we present a multifunctional additive of tris(2 H-hexafluoroisopropyl)borate (THFPB) for preparing Mg(BH4)2-based electrolytes. By virtue of the strong electron-acceptor ability of the THFPB molecule, a transparent and high-concentration Mg(BH4)2/THFPB-diglyme (DGM) electrolyte (0.5 M, almost 50 times higher than that of the pristine Mg(BH4)2-DGM electrolyte) is first obtained, which shows dramatic performance improvements, including high ionic conductivity (3.72 mS cm-1 at 25 °C) and high Mg plating/stripping Coulombic efficiency (>99%). The newly-generated active cation and anion species revealed by Raman, NMR and MS spectra, increase the electrochemical potential window from 1.8 V to 2.8 V vs Mg on stainless steel electrode, rendering electrolytes the ability to examine high voltage cathodes. More importantly, on account of the non-nucleophilicity of active electrolyte species, we present the first example of magnesium-sulfur (Mg-S) batteries using Mg(BH4)2-based electrolytes, which exhibit a high discharge capacity of 955.9 and 526.5 mA h g-1 at the initial and 30th charge/discharge cycles, respectively. These achievements not only provide an efficient and specific strategy to eliminate the major roadblocks facing Mg(BH4)2-based electrolytes but also highlight the profound effect of functional additives on the electrochemical performances of unsatisfied Mg-ion electrolytes.