The potential of B 4 C as a metal-free catalyst for vanadium redox reactions is investigated by first-principles calculations. Results show that the central carbon atom of B 4 C can act as a highly active reaction site for redox reactions , due primarily to the abundant unpaired electrons around it. The catalytic effect is then verified experimentally by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests, both of which demonstrate that B 4 C nanoparticles can enhance the kinetics for both V 2+ /V 3+ and VO 2+ /VO 2 + redox reactions, indicating a bi-functional effect. The B 4 C-nanoparticle-modified graphite felt electrodes are finally prepared and tested in vanadium redox flow batteries (VRFBs). It is shown that the batteries with the prepared electrodes exhibit energy efficiencies of 88.9% and 80.0% at the current densities of 80 and 160 mA cm −2 , which are 16.6% and 18.8% higher than those with the original graphite felt electrodes. With a further increase in current densities to 240 and 320 mA cm −2 , the batteries can still maintain energy efficiencies of 72.0% and 63.8%, respectively. All these results show that the B 4 C-nanoparticle-modified graphite felt electrode outperforms existing metal-free catalyst modified electrodes , and thus can be promising electrodes for VRFBs.
P2-Na0.6Li0.11Fe0.27−xMn0.62YxO2 (x = 0, 0.5%, 1%, and 2%) cathode materials were successfully prepared using a traditional solid-state method with ball milling-assisted modification. The effect of Y-doping on the crystal structure, grain size, morphology and sodium storage performance of Na0.6Li0.11Fe0.27Mn0.62O2 was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge–discharge cycling tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the ball-milling pre-treatment method could effectively reduce the grain size and mitigate the aggregation of Na0.6Li0.11Fe0.27Mn0.62O2. Additionally, reasonable Y-doping (x = 1%) significantly enhances the rate capability and cycling stability of Na0.6Li0.11Fe0.27Mn0.62O2via improving the Na+ diffusion kinetics and the reversibility of the oxygen redox reaction. These results indicate that Na0.6Li0.11Fe0.26Mn0.62Y0.01O2 is a promising candidate material for high-rate and long-life cathodes for Na-ion battery application.
Organic compounds have been utilized in rechargeable batteries as electrode materials on account of their designable structures and reversible redox properties. However, most of them suffer from problems with dissolution resulting in poor electrochemical performance. In this work, we adapt a sodium salt of tetracyanoquinodimethane (NaTCNQ) to work as a high redox potential cathode material in sodium ion batteries (SIBs). A porous carbon coated separator is demonstrated to be an adsorption layer and prevents the dissolved active material from migrating to the anode side. The NaTCNQ cell assembled with a carbon layer containing 5% activated carbon (AC) exhibits a higher initial capacity and greatly improved cycling stability. Using a conductive adsorption layer in organic redox batteries is a promising pathway to develop high performance organic electrode materials for SIBs.
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