Zili Cui

Equilibrium voltage and overpotential variation of nonaqueous Li–O2 batteries using the galvanostatic intermittent titration technique

The Li–air (or Li–O2) battery has attracted wide attention, since it has the highest theoretical specific gravimetric energy density. In spite of the rapid progress made on improving its cyclic performance and reducing its voltage polarization, many key issues on thermodynamics and kinetics in nonaqueous Li–O2 batteries are still unresolved. In this study, by using the galvanostatic intermittent titration technique, several novel phenomena have been observed, such as zero voltage gap for the open circuit voltage (OCV) between charging and discharging, asymmetrical polarization behaviours at different current densities and temperatures, a continuous increase of overpotential during charging, and a negative temperature coefficient of the cells thermodynamic equilibrium voltage. These results could inspire other researchers to comprehensively investigate the complicated reaction mechanisms, thermodynamics, and kinetic properties of the Li–air battery, as well as other advanced batteries.

Hydrogen substituted graphdiyne as carbon-rich flexible electrode for lithium and sodium ion batteries

Organic electrodes are potential alternatives to current inorganic electrode materials for lithium ion and sodium ion batteries powering portable and wearable electronics, in terms of their mechanical flexibility, function tunability and low cost. However, the low capacity, poor rate performance and rapid capacity degradation impede their practical application. Here, we concentrate on the molecular design for improved conductivity and capacity, and favorable bulk ion transport. Through an in situ cross-coupling reaction of triethynylbenzene on copper foil, the carbon-rich frame hydrogen substituted graphdiyne film is fabricated. The organic film can act as free-standing flexible electrode for both lithium ion and sodium ion batteries, and large reversible capacities of 1050 mAh g−1 for lithium ion batteries and 650 mAh g−1 for sodium ion batteries are achieved. The electrode also shows a superior rate and cycle performances owing to the extended π-conjugated system, and the hierarchical pore bulk with large surface area.Flexible batteries have been used to power wearable smart electronics and implantable medical devices. Here, the authors report a carbon-rich flexible hydrogen substituted graphdiyne electrode exhibiting superior electrochemical performance in lithium and 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.

High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy toward Facile Synthesis

Abstract It is urgent to seek high performance solid polymer electrolytes (SPEs) via a facile chemistry and simple process. The lithium salts are composed of complex anions that are stabilized by a Lewis acid agent. This Lewis acid can initiate the ring opening polymerization. Herein, a self‐catalyzed strategy toward facile synthesis of crosslinked poly(ethylene glycol) diglycidyl ether‐based solid polymer electrolyte (C‐PEGDE) is presented. It is manifested that the poly(ethylene glycol) diglycidyl ether‐based solid polymer electrolyte possesses a superior electrochemical stability window up to 4.5 V versus Li/Li+ and considerable ionic conductivity of 8.9 × 10−5 S cm−1 at ambient temperature. Moreover, the LiFePO4/C‐PEGDE/Li batteries deliver stable charge/discharge profiles and considerable rate capability. It is demonstrated that this self‐catalyzed strategy can be a very effective approach for high performance solid polymer electrolytes.

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.

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.

Construction of Large-Area Uniform Graphdiyne Film for High-Performance Lithium-Ion Batteries

Large-area graphdiyne film is constructed by heat treatment, including thermally induced evaporation and a cross-coupling reaction process. The growth mechanism is proposed based on the observation and characterization that the heating temperature plays an important role in the evaporation of oligomers and in triggering the thermal cross-coupling reaction, whereas the heating duration mainly determines the execution of the thermal cross-coupling reaction. By controlling the heat-treatment process, a graphdiyne film with uniform morphology and good conductivity is obtained. The improved GDY film based electrodes deliver good interfacial contact and more lithium storage sites; thus leading to superior electrochemical performance. A reversible capacity of 901 mAh g-1 is achieved. Specifically, the electrodes exhibit excellent rate performance, with which a capacity of 430 mAh g-1 is maintained at a rate as high as 5 A g-1 . These advantages mean that the uniform graphdiyne film is a good candidate for the fabrication of a flexible and high-capacity electrode material.