A Fast-Charge Graphite Anode with a Li-Ion-Conductive, Electron/Solvent-Repelling Interface

Graphite has been serving as the key anode material of rechargeable Li-ion batteries, yet is difficultly charged within a quarter hour while maintaining stable electrochemistry. In addition to a defective edge structure that prevents fast Li-ion entry, the high-rate performance of graphite could be hampered by co-intercalation and parasitic reduction of solvent molecules at anode/electrolyte interface. Conventional surface modification by pitch-derived carbon barely isolates the solvent and electrons, and usually lead to inadequate rate capability to meet practical fast-charge requirements. Here we show that, by applying a MoOx-MoNx layer onto graphite surface, the interface allows fast Li-ion diffusion yet blocks solvent access and electron leakage. By regulating interfacial mass and charge transfer, the modified graphite anode delivers a reversible capacity of 340.3 mAh g-1 after 4000 cycles at 6 C, showing promises in building 10-min-rechargeable batteries with a long operation life.

Kinetic Limits of Graphite Anode for Fast-Charging Lithium-Ion Batteries

Fast-charging lithium-ion batteries are highly required, especially in reducing the mileage anxiety of the widespread electric vehicles. One of the biggest bottlenecks lies in the sluggish kinetics of the Li+ intercalation into the graphite anode; slow intercalation will lead to lithium metal plating, severe side reactions, and safety concerns. The premise to solve these problems is to fully understand the reaction pathways and rate-determining steps of graphite during fast Li+ intercalation. Herein, we compare the Li+ diffusion through the graphite particle, interface, and electrode, uncover the structure of the lithiated graphite at high current densities, and correlate them with the reaction kinetics and electrochemical performances. It is found that the rate-determining steps are highly dependent on the particle size, interphase property, and electrode configuration. Insufficient Li+ diffusion leads to high polarization, incomplete intercalation, and the coexistence of several staging structures. Interfacial Li+ diffusion and electrode transportation are the main rate-determining steps if the particle size is less than 10 μm. The former is highly dependent on the electrolyte chemistry and can be enhanced by constructing a fluorinated interphase. Our findings enrich the understanding of the graphite structural evolution during rapid Li+ intercalation, decipher the bottleneck for the sluggish reaction kinetics, and provide strategic guidelines to boost the fast-charging performance of graphite anode.

Mechanistic investigation into flow-through electrochemical oxidation of sulfanilamide for groundwater using a graphite anode

The technical effectiveness/merit of electrochemical oxidation (EO) has been recognized. Nonetheless, its practical application to groundwater remediation has not been fully implemented due to several technical challenges. To overcome the technical incompleteness, this study adopted a graphite anode in the flow-through system and studied the mechanistic roles of a graphite anode. To this end, groundwater contaminated with sulfanilamide was remediated by means of EO, and sulfanilamide oxidation was quantitatively determined in this study. Approximately 60% of sulfanilamide was degraded at the anode zone, and such observation offered that the removal of sulfanilamide was not closely related with current variations (10-100 mA). However, this study delineated that sulfanilamide removal is contingent on the flow speed. For example, the removal of sulfanilamide was lowered from 59 to 25% owing to a short contact time when the flow velocity was increased from 0.14 to 0.55 cm/min. This study also delineated that a shorter anode-cathode distance could offer a favorable chance to enhance the removal of sulfanilamide even under an identical current. A shorter distance could offer a chance to save energy due to the lower voltage operation. This study also offered that chloride (Cl^-) and sulfate (SO₄^2-) electrolytes served a crucial role in the generation of active species. In contrast, bicarbonate (HCO₃^-) and synthetic groundwater electrolytes impeded the oxidation rate because HCO₃^- scavenged the other active species. In an effort to seek the oxidation mechanisms of a graphite anode, scavenger, cyclic voltammetry test, and electron https://en.wikipedia.org/wiki/Electron_paramagnetic_resonanceparamagnetic resonance (EPR) analysis were done. From a series of the tests, it was inferred that a graphite anode did not directly affect the generation of the active species. Thus, the prevalence of the oxygenated functional groups on an anode surface could be the main mechanism in sulfanilamide removal due to the enhanced electron transfer.

Electro-oxidation by graphite anode for naphthenic acids degradation, biodegradability enhancement and toxicity reduction

Electro-oxidation (EO) by using graphite anode and at relatively low current densities was successfully applied for the degradation of commercial naphthenic acids (NAs) mixture in water samples. At current densities of 0.5, 2.5, and 5 mA/cm², acid extractable fraction (AEF) was removed by 42.2%, 57.0% and 67.9%, respectively, while classical NAs were degraded by 76.9%, 77.6% and 82.4%, respectively. EO reactivity towards NAs increased with increasing the carbon number (n) and was higher for cyclic NAs compared to the acyclic component. Oxidized NAs containing O₃ and O₄ were also degraded effectively during EO. The biodegradability of organics in the NA mixture was clearly improved by 1.7, 2.5 and 2.7 folds when the samples were pre-treated with EO at current densities of 0.5, 2.5, and 5 mA/cm², respectively. The aromatic fraction in the commercial NA mixture consisted mainly of single-ring aromatics and was degraded effectively by EO. Biodegradation alone was able to reduce the toxicity of the commercial NA mixture towards Vibrio fischeri; however, the combination of EO with biodegradation resulted in a complete removal of the toxicity, showing a synergistic effect of combining these two processes. Coupling EO with aerobic biodegradation can result in an effective and energy-efficient treatment option for NA-bearing waters such as oil sands process water (OSPW) and refinery effluents.

Spontaneous modification of graphite anode by anthraquinone-2-sulfonic acid for microbial fuel cells

In this study, anthraquinone-2-sulfonic acid (AQS), an electron transfer mediator, was immobilized onto graphite felt surface via spontaneous reduction of the in situ generated AQS diazonium cations. Cyclic voltammetry (CV) and energy dispersive spectrometry (EDS) characterizations of AQS modified graphite demonstrated that AQS was covalently grafted onto the graphite surface. The modified graphite, with a surface AQS concentration of 5.37 ± 1.15 × 10(-9)mol/cm(2), exhibited good electrochemical activity and high stability. The midpoint potential of the modified graphite was about -0.248 V (vs. normal hydrogen electrode, NHE), indicating that electrons could be easily transferred from NADH in bacteria to the electrode. AQS modified anode in MFCs increased the maximum power density from 967 ± 33 mW/m(2) to 1872 ± 42 mW/m(2). These results demonstrated that covalently modified AQS functioned as an electron transfer mediator to facilitate extracellular electron transfer from bacteria to electrode and significantly enhanced the power production in MFCs.