Deyang Qu

Investigation of the Li-S Battery Mechanism by Real-Time Monitoring of the Changes of Sulfur and Polysulfide Species during the Discharge and Charge

The mechanism of the sulfur cathode in Li-S batteries has been proposed. It was revealed by the real-time quantitative determination of polysulfide species and elemental sulfur by means of high-performance liquid chromatography in the course of the discharge and recharge of a Li-S battery. A three-step reduction mechanism including two chemical equilibrium reactions was proposed for the sulfur cathode discharge. The typical two-plateau discharge curve for the sulfur cathode can be explained. A two-step oxidation mechanism for Li2S and Li2S2 with a single chemical equilibrium among soluble polysulfide ions was proposed. The chemical equilibrium among S52-, S62-, S72-, and S82- throughout the entire oxidation process resulted for a single flat recharge curve in Li-S batteries.

A room-temperature liquid metal-based self-healing anode for lithium-ion batteries with an ultra-long cycle life

Benefiting from fluidity and surface tension, materials in a liquid form are one of the best candidates for self-healing applications. This feature is highly desirable for improving the life cycle of lithium-ion batteries (LIBs) because the volume expansion/contraction during the cycles of high-capacity anodes such as Si and Sn can result in mechanical fracture and lead to inferior cycle performance. Here, we report a novel room-temperature liquid metal (LM) as the anode to improve the cycle life of LIBs. The LM anode comprises an alloy of Sn and Ga, a liquid at room temperature with inherent self-healing properties, as confirmed by the in situ and ex situ analyses. Because both Ga and Sn have high theoretical capacities (769 and 990 mA h g−1, respectively), the resulting LM anode delivers a high capacity of 775, 690, and 613 mA h g−1 at the rate of 200, 500, and 1000 mA g−1, respectively. There was no obvious decay in more than 4000 cycles with a capacity of ∼400 mA h g−1 at 4000 mA g−1, realizing the best cycle performance among all metal anodes.

Hydrogen Ion Supercapacitor: A New Hybrid Configuration of Highly Dispersed MnO2 in Porous Carbon Coupled with Nitrogen-Doped Highly Ordered Mesoporous Carbon with Enhanced H-Insertion

A new configuration of hydrogen ion supercapacitors was reported. A positive electrode composed of pseudocapacitive MnO2, highly dispersed into active porous carbon through an impregnation method, was combined with a nitrogen-doped highly ordered mesoporous carbon with enhanced electrochemical hydrogen insertion capacity as a negative electrode. During the operation, hydrogen ion shuttled between MnO2 and carbon electrodes. The MnO2 was formed on the surface of nanostructured carbon through a spontaneous redox reaction. Operating in an aqueous neutral solution, the hybrid device demonstrated an extended working voltage to ∼2.1 V with good cycle life.

Reaction between Lithium Anode and Polysulfide Ions in a Lithium–Sulfur Battery

The reaction between polysulfides and a lithium anode in a Li-S battery was examined using HPLC. The results demonstrated that the polysulfide species with six sulfur atoms or more were reactive with regard to lithium metal. Although the reaction can be greatly inhibited by the addition of LiNO3 in the electrolyte, LiNO3 cannot form a stable protection layer on the Li anode to prevent the reaction during storage.

Preferential Solvation of Lithium Cations and Impacts on Oxygen Reduction in Lithium-Air Batteries.

The solvation of Li+ with 11 nonaqueous solvents commonly used as electrolytes for lithium batteries was studied. The solvation preferences of different solvents were compared by means of electrospray mass spectrometry and collision-induced dissociation. The relative strength of the solvent for the solvation of Li+ was determined. The Lewis acidity of the solvated Li+ cations was determined by the preferential solvation of the solvent in the solvation shell. The kinetics of the catalytic disproportionation of the O2•- depends on the relative Lewis acidity of the solvated Li+ ion. The impact of the solvated Li+ cation on the O2 redox reaction was also investigated.

Stability of the Solid Electrolyte Interface on the Li Electrode in Li–S Batteries

By means of high performance liquid chromatography-mass spectroscopy, the concentration of sulfur and polysulfides was determined in nonaqueous electrolytes. The stability of sulfur and Li in eight electrolytes was studied quantitatively. It was found that sulfur reacted with Li in most of the commonly used electrolytes for lithium-sulfur batteries. The reaction products between sulfur and Li were qualitatively identified. In some cases, the solid electrolyte interface on the Li can successfully prevent the interaction between S and Li; however, it was found that the solid electrolyte interface was damaged by polysulfide ions.

Exploring polycyclic aromatic hydrocarbons as an anolyte for nonaqueous redox flow batteries

Nonaqueous redox flow batteries (RFB) can potentially achieve high energy density due to the extended operating voltage windows and redox-active material candidates. However, the development of reversible anode materials with a low redox potential and high solubility is still one of the main challenges. Here, we systematically explore polycyclic aromatic hydrocarbons (PAHs) and their corresponding radical anions (PAH˙n−) as anode redox-active couples with a combination of experimental and computational methods. The results reveal that naphthalene and its radical anion (Nap/Nap˙−) are a promising anode redox-active couple. Paired with catholytes separately containing ferrocenium hexafluorophosphate (FcPF6) and TEMPO, the resulting RFBs can provide theoretical maximum energy densities of 39 W h L−1 and 208 W h L−1, respectively, which are much higher than that of a traditional all-vanadium flow battery (25 W h L−1). As proofs of concept, both static-mode and flow-mode of the as-proposed RFBs are assembled and can deliver dozens of consecutive charge–discharge cycles.

Dual carbon-protected metal sulfides and their application to sodium-ion battery anodes

Metal sulfides are considered as promising anode materials for sodium ion batteries owing to their good redox reversibility and relatively high theoretical capacity. However, their cycle life and rate capability are still unsatisfactory because of poor conductivity and a large volume change during the discharge/charge processes. A facile method for preparing dual carbon-protected metal sulfides is reported. Metal diethyldithiocarbamate complexes are used as precursors. The synthesis only involves a co-precipitation of metal diethyldithiocarbamate complexes with graphene oxide and a subsequent thermal pyrolysis. As an example, N-doped carbon-coated iron sulfides wrapped in the graphene sheets (Fe1−xS@NC@G) are prepared and used as the anode material for a sodium ion battery. The as-synthesized Fe1−xS@NC@G electrode exhibits a high reversible capacity (440 mA h g−1 at 0.05 A g−1), outstanding cycling stability (95.8% capacity retention after 500 cycles at 0.2 A g−1), and good rate capability (243 mA h g−1 at 10 A g−1). Coupled with a Na3V2(PO4)2@C cathode, the full battery exhibits a high capacity retention ratio of 96.5% after 100 cycles and an average output voltage of ca. 2.2 V. More importantly, the proposed synthesis route is universal and can be extended to fabricate diverse transition metal sulfide-based composites with a dual carbon-protected nanostructure for advanced alkali ion batteries.

Modern Applications of Green Chemistry: Renewable Energy

Abstract Renewable energy is derived from natural and sustainable processes. For example, solar energy, wind energy, and geothermal energy are types of renewable energy. The challenges to using renewable energy include energy harvesting, energy storage, and energy delivery. In this chapter, electrochemical energy storage and delivery methods will be introduced. To be specific, batteries and fuel cells with various chemistries will be covered. The difference between heat engines and chemical energy storage devices are discussed in the scope of the second law of thermodynamics.

Electrochemical Hydrogen Storage in Facile Synthesized Co@N-Doped Carbon Nanoparticle Composites

A Co@nitrogen-doped carbon nanoparticle composite was synthesized via a facile molecular self-assembling procedure. The material was used as the host for the electrochemical storage of hydrogen. The hydrogen storage capacity of the material was over 300 mAh g-1 at a rate of 100 mAg-1. It also exhibited superior stability for storage of hydrogen, high rate capability, and good cyclic life. Hybridizing metallic cobalt nanoparticle with nitrogen-doped mesoporous carbon is found to be a good approach for the electrochemical storage of hydrogen.