Search

Energy storage materials 50, 464 - 472 (2022). doi:10.1016/j.ensm.2022.05.048, A cathode/anode compatible aqueous zinc triflate electrolyte is proposed by reorganizing the solvation structure of the electrolyte using an acetonitrile co-solvent. Acetonitrile notably alters the hydrogen bonds of the electrolyte, reducing the activity of water. Using this electrolyte, a ZnǁV2O5 full-cell exhibits high Coulombic efficiency, long cycle life and high rate capability. The interactions between electrolyte, cathode and Zn anode are clarified based on comprehensive in operando and ex situ experiments and molecular dynamics simulations. The addition of acetonitrile does not change the bulk ion storage of V2O5, but the unique electrode-electrolyte interfacial films with specific compositions and spatial distribution protect the Zn and V2O5 electrodes and improve the interfacial kinetics of the electrodes, thus significantly promoting the cycling performance of the full cell. This cathode/anode compatible electrolyte can overcome the challenges of both the cathode and anode which would promote aqueous rechargeable zinc batteries into practical application., Published by Elsevier, Amsterdam

Soluble redox mediators (RMs) are one of the most promising approaches for reducing charging overpotentials in Li–O2 batteries. However, this auspicious strategy still in its infancy and raises new scientific problems needing to be clarified, such as the influence of RMs with different charge–transfer or different molecular structure (same redox functional group) on Li2O2 oxidation behavior. Herein, the realities of Li2O2 oxidation by some RMs, including lithium bromide, tetrathiafulvalene, 2,2,6,6–tetramethyl–1–piperidinyloxy, and 2–azaadamantane–N–oxyl, were investigated using detailed experimental results and first–principles calculations. Among these RMs studied, single electron–reaction RMs exhibited a more stable charging curve at lower potential than that of multiple electron–reaction RMs. Besides, the RM molecular with smaller steric effects and higher electron–donating power exhibited higher catalytic activity thus a lower charging overpotential. These findings offered a guidance direction for subsequent explorations and optimization of high performance RMs, which might further facilitate development for Li–O2 batteries.

The difficult Mg2+ desolvation of chloride-based electrolytes and slow Mg2+ diffusion in the cathode seriously hinder the electrochemical performance of Mg-ion batteries (MIBs). To solve these problems, a high performance MIB cell was built using a VS2 nanosheet cathode and with 0.4 M (PhMgCl)2-AlCl3/tetrahydrofuran (APC/THF) and 50 wt.% 1-butyl-1-methylpiperidinium chloride (PP14Cl) as the electrolyte. The resulting system showed a large capacity of 348 mA h g−1 at 20 mA·g−1 current density and excellent rate capability with a 214 mA h g−1 capacity at 2.0 A·g−1 current density. A thorough experimental and theoretical study showed that Mg2+ desolvation energy was reduced from 3.0 to 0.67 eV under the catalytic effects of PP14+. Moreover, large-sized PP14+ was inserted into the VS2 interlayer during the first discharge and permanently resided in the material. As a result, the interlayer spacing of VS2 was largely expanded, which improved the Mg2+ diffusion coefficient by three orders of magnitude to 10−10–10−12 cm−2 s. The reduced Mg2+ desolvation energy by the catalytic effects of PP14+, together the improved Mg2+ diffusion kinetics by the interlayer expansion effect of PP14+, provided a significant implement way towards development of high performance and practical MIBs by electrolyte regulation.

Cobalt sulfides based on conversion mechanisms are considered as promising anode materials for sodium-ion batteries due to their appropriate working voltage and high practical capacities. But the severe volume change and structure transformation make their cycle stability and rate capability unsatisfactory. In this study, metal-organic framework derived Co9S8@carbon yolk-shell nanocages (Co9S8@CYSNs) was prepared and its direct conversion mechanism was carefully demonstrated for the first time by various spectroscopic techniques and first-principles calculations. The unique hierarchical structure of Co9S8@CYSNs composed of Co9S8 nanoparticles dispersed in amorphous carbon matrix inside a rigid carbon shell was capable of accelerating the conversion reaction, shortening the Na+ diffusion distance and providing a fast electron transport channel. Benefiting from the accelerated electrochemical reactions and high activities of nanosized particles, the Co9S8@CYSNs exhibited a large discharge capacity of 549.4 mA h g-1 at 0.1 A g-1. In addition, a superior rate performance of 100 mA h g-1 at 10 A g-1 and excellent cycle stability with a very low capacity decay of 0.019% per cycle over 800 cycles at 10.0 A g-1 were achieved because of the confine effect of the carbon shell and improved charge transfer reactions of the electrode.

Hierarchical flower-like VS 2 nanosheets assemblies are successfully synthesized via a facile solvothermal method, and their Na + storage behavior is systematically studied with respect to the galvanostatic charge-discharge profiles, cyclic voltammograms, rate capability and long-term cycle stability. With a well-controlled cut-off voltage (3.0–0.3 V) and suitable electrolyte (1.0 M NaCF 3 SO 3 in diglyme), flower-like VS 2 delivers a high reversible capacity of around 600 mAh g −1 at 0.1 A g −1 and excellent cycle stability with 83% and 87% of its initial capacities retained after 700 cycles at 2 and 5 A g −1 , respectively. Remarkably, the VS 2 anode shows a high initial Coulombic efficiency of 94% and nearly 100% in the subsequent cycles, which points to the promising application of the present material in the commercial sodium-ion batteries. Moreover, VS 2 nanostructures also exhibit superior rate performance with a discharge capacity of 277 mAh g −1 at a current density of as high as 20 A g −1 . Quantitative kinetic analysis indicates that the sodium storage is governed by a pseudocapacitance mechanism, particularly at high current rates. Combined with ex-situ Raman, HRTEM and SAED characterizations further reveal that the Na + storage is based on electrochemical intercalation-de-intercalation reactions.

Two-dimensional (2D) carbides, MXenes, have shown promise for electrochemical energy storage, but most studies were conducted on titanium carbides. Herein we report on Li insertion into a 2D Nb4C3Tx MXene, formed by etching aluminum from Nb4AlC3 in HF at room temperature. The theoretical capacity of Nb4C3Tx has not been studied, but it displayed a higher capacity than as-produced titanium carbide and other MXenes, when tested as anode for lithium ion batteries. In addition, the charge/discharge capacity of the Nb4C3Tx anode increases with cycling. For instance, after 100 charge/discharge cycles, the specific capacity increased from 310 mA h g−1 (194 mA h cm−3) to 380 mA h g−1 (238 mA h cm−3), at a current density of 0.1 A g−1, and the capacity increased from 116 mA h g−1 (73 mA h cm−3) to 320 mA h g−1 (200 mA h cm−3) at 1 A g−1. Excellent rate capability and superior long-term stability at the ultrahigh rates have been demonstrated. This work is expected to inspire further exploration of MXenes for high-performance Li-ion batteries and capacitors. Since Nb4C3Tx is just one of many MXenes, there is much room for improving the accessibility of the electronically conducting layered structures of MXenes and achieving a better electrochemical performance.