Competitive Coordination of Sodium Ions for High-Voltage Sodium Metal Batteries with Fast Reaction Speed.

The unstable electrode-electrolyte interface and the narrow electrochemical window of normal electrolytes hinder the potential application of high-voltage sodium metal batteries. These problems are actually related to the solvation structure of the electrolyte, which is determined by the competition between cations coordinated with anions or solvent molecules. Herein, we design an electrolyte incorporating ethyl (2,2,2-trifluoroethyl) carbonate and fluoroethylene carbonate, which facilitates a pronounced level of cation-anion coordination within the solvation sheath by enthalpy changes to reduce the overall coordination of cation-solvents and increase sensitivity to salt concentration. Such an electrolyte regulated by competitive coordination leads to highly reversible sodium plating/stripping with extended cycle life and a high Coulombic efficiency of 98.0%, which is the highest reported so far in Na||Cu cells with ester-based electrolytes. Moreover, 4.5 V high-voltage Na||Na3V2(PO4)2F3 cells exhibit a high rate capability up to 20 C and an impressive cycling stability with an 87.1% capacity retention after 250 cycles with limited Na. The proposed strategy of solvation structure modification by regulating the competitive coordination of the cation provides a new direction to achieve stable sodium metal batteries with high energy density and can be further extended to other battery systems by controlling enthalpy changes of the solvation structure.

Ethanol Solvent Used in Constructing Ultra-Low-Temperature Zinc-Ion Capacitors with a Long Cycling Life.

Zinc-ion capacitors (ZICs) gain enormous attraction for their high power density, low cost, and long life, but their poor low-temperature performance is still a challenge due to the dissatisfactory freezing point of aqueous electrolyte solution. It is difficult for them to meet the requirements in cold environments as well as the extreme low temperature and severe temperature fluctuations in aerospace environments. Herein, ethanol (EtOH) solvent with ZnCl2 is used as an electrolyte to address these issues. Benefiting from the low freezing point (-114 °C) of EtOH, the ZIC with the ZnCl2/EtOH electrolyte can be operated at an ultralow temperature of -78 °C. It also demonstrates long cycling stability over 30,000 cycles. Such an enhancement is attributed to the unique properties of [ZnCl(EtOH)5]+ that can stabilize the coordination environment of Zn2+, slow the diffusivity, and raise the nucleation overpotential, leading to uniform Zn plating/stripping and subsequently suppressing dendrite growth. Meanwhile, the lower activation energy in ZnCl2/EtOH than that in ZnSO4/H2O electrolytes endows the ZIC excellent charge transfer properties. This work provides a fascinating electrolyte and a feasible pathway for ultra-low-temperature ZICs with a long cycling life.

A Chlorine-Based Redox Electrochemical Capacitor.

Electrochemical capacitors are under the spotlight due to their high power density, but they have a low energy density. Redox electrolytes have emerged as a promising approach to design high-energy electrochemical energy storage devices. Herein, a chlorine-based redox electrochemical capacitor is reported in an ionic liquid electrolyte. The commercial activated carbon is employed as the working electrode to render the reversible redox of chloride ions in an ionic liquid, by the restriction of micropores on neutral chlorine. The carbon material can simultaneously provide electrical double-layer capacitance. The effective integration of a chlorine redox reaction and electrical double layer allows for high-energy electrochemical capacitors. By this means, a rechargeable chlorine-based redox electrochemical capacitor with reversible capacity and good rate capability and cycling stability is obtained. This work offers a solution for a new type of high-energy electrochemical capacitors.

Synthesis of Few-Layer Graphene Sheets from Waste Expanded Polystyrene by Dense Fe Cluster Catalysis.

Graphene sheets have a vast number of potential applications due to their excellent properties. However, poor quality and harsh preparation conditions restrict their application. Here, few-layer graphene (FLG) sheet powder with high quality has been synthesized from waste expanded polystyrene (EPS) at low temperature by dense Fe cluster catalysis. The micron-sized FLG sheets comprising about three layers show high crystallinity and good electrical conductivity that are comparable to those of the shear-exfoliated graphene nanoplatelets. More than 70% carbon yield of FLG sheets from cheap EPS and their safe, controllable synthesis conditions make it easy to expand production. The catalytic formation mechanism of FLG sheets is studied.