Self-discharge, which refers to voltage depression when a power source is removed, is a crucial issue for supercapacitors (SCs). Self-discharge results in Coulombic efficiency loss and energy dissipation, and thus restricts the charge storage performance of SCs. A cost-effective and facile strategy for addressing self-discharge is newly developed in this work. It is found that self-discharge involves charge redistribution and Faradaic side reactions, which are closely associated with the pore size of activated carbon electrodes. Importantly, the pore size distribution (and thus self-discharge) can be controlled by the binder type. Specifically, a binder that maintains high macropore and mesopore fractions can effectively mitigate self-discharge. The fundamental reasons for this finding are examined. The effects of the charging rate, holding time at the full charging voltage, operation temperature, and charging cutoff voltage on the self-discharge of SCs prepared using various binders are investigated. The data reveal that binder selection also influences SC reliability in terms of the aging rate at elevated temperature and high voltage, leakage current, and gas evolution during operation.
Conventional vapor–liquid–solid mechanism of nanowire growth opens up new opportunities of fabricating nanowires with controllable morphologies and aspect ratios. However, gaseous precursors have disadvantages of high material and processing cost, high toxicity, and limited scalability. By contrast, synthesizing nanowires via solid–liquid–solid mechanism could be
a facile alternative since the low cost and nontoxic solid precursor is adopted in the process. In this study, the cooling control is found to be very critical for the solid–liquid–solid nanowire growth. Without a sufficient negative vertical temperature gradient, the nucleation and continuous growth of silicon nanowires could not occur. High volume gas flow cooling, fluctuating the heating temperature, decreasing the cooling rate, and applying a heat sink are all efficacious to promote silicon nanowire formation. In addition to the nanowires formed under high gas flow cooling on the silicon wafer sputtered with a nickel thin film, the solid–liquid–solid mechanism-derived silicon nanowire growth can also be economically achieved by adopting a solution-based coating of a nickel precursor onto the silicon substrate paired with a programmed slow cooling condition without using any gas, which could be transferred to other eutectic systems for cost-effective nanomaterial fabrication.
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A low-level metallic lithium thermal prelithiation strategy has been developed for boosting the performance of SiO anode materials with aqueous slurry processability. This facile prelithiation method can alter the phase and crystalline size of lithium silicates by controlling the parameters such as lithium contents and processing temperatures. The prelithiated graphene-SiO composite anode material thus obtained under the optimized condition offers a high reversible capacity of 1062 mAh g−1 and the initial Coulombic efficiency of 80.8 %. Additionally, both the cycle life and cycling Coulombic efficiency are extremely stable, preserving over 90.3 % of the capacity after 200 cycles and more than 99.7 % of the efficiency on average during cycling. The significantly enhanced battery performance of the prelithiated SiO anode materials is owing to the size control of crystal silicon and Li2SiO3 phases. The existence of Li2Si2O5 and suppression of Li4SiO4 formation also guarantee homogeneous prelithiation results. This facile low-level prelithiation approach is remarkably effective to improve the initial Coulombic efficiency for commercial SiO anode materials and simultaneously maintain superior reversible capacity, cycle life, cycling efficiency, and aqueous slurry processability.
