Engineering topics
Han, Fudong
Publications and source records attributed to Han, Fudong.
Thermodynamics and Kinetics of Sulfur Cathode during Discharge in MgTFSI 2 -DME Electrolyte
Rechargeable magnesium/sulfur battery is of significant interest because its energy density (1700 Wh kg -1 and 3200 Wh L -1 ) is among the highest of all battery chemistries (lower than Li/O 2 and Mg/O 2 but comparable to Li/S), and Mg metal allows reversible operation (100% Coulombic efficiency) with no dendrite formation. This great promise is already justified in some early reports. However, lack of mechanistic study of sulfur reaction in the Mg cation environment has severely hindered our understanding and prevents effective measures for performance improvement. In this work, the very first systematic fundamental study on Mg/S system is conducted by combining experimental methods with computational approach. The thermodynamics and reaction pathway of sulfur cathode in MgTFSI 2 –DME electrolyte, as well as the associated kinetics are thoroughly investigated. The results here reveal that sulfur undergoes a consecutive staging pathway in which the formation and chain-shortening of polysulfide occur at early stage accompanied by the dissolution of long-chain polysulfide, and solid-state transition from short-chain polysulfide to magnesium sulfide occurs at late stage. Finally, the former process is much faster than the latter due to the synergetic effect of the mediating effect of dissolved polysulfide and the fast diffusion of Mg ion in the amorphous intermediate.
Reducing Mg Anode Overpotential via Ion Conductive Surface Layer Formation by Iodine Additive
Electrolytes that are able to reversibly deposit/strip Mg are crucial for rechargeable Mg batteries. The most researched complex electrolytes based on Lewis acid-base chemistry are expensive, difficult to be synthesized, and show limited anodic stability. Conventional electrolytes using simple salts such as Mg(TFSI) 2 can be readily synthesized, but Mg deposition/stripping in these simple salt electrolytes is accompanied by a large overpotential due to the formation of a surface layer on the Mg metal with a low Mg ion conductivity. In this work, the overpotential for Mg deposition/stripping in a simple salt, Mg(TFSI) 2 -1,2-dimethoxyethane (DME), electrolyte is significantly reduced by adding a small concentration of iodine (≤50 × 10 –3 m) as an additive. Mechanism studies show that an Mg ion conductive solid MgI2 layer is formed on the surface of the Mg metal and acts as a solid electrolyte interface. With the Mg(TFSI) 2 -DME-I 2 electrolyte, a very small voltage hysteresis is achieved in an Mg-S full cell.
Flexible Aqueous Li‐Ion Battery with High Energy and Power Densities
Abstract A flexible and wearable aqueous symmetrical lithium‐ion battery is developed using a single LiVPO 4 F material as both cathode and anode in a “water‐in‐salt” gel polymer electrolyte. The symmetric lithium‐ion chemistry exhibits high energy and power density and long cycle life, due to the formation of a robust solid electrolyte interphase consisting of Li 2 CO 3 ‐LiF, which enables fast Li‐ion transport. Energy densities of 141 Wh kg −1 , power densities of 20 600 W kg −1 , and output voltage of 2.4 V can be delivered during >4000 cycles, which is far superior to reported aqueous energy storage devices at the same power level. Moreover, the full cell shows unprecedented tolerance to mechanical stress such as bending and cutting, where it not only does not catastrophically fail, as most nonaqueous cells would, but also maintains cell performance and continues to operate in ambient environment, a unique feature apparently derived from the high stability of the “water‐in‐salt” gel polymer electrolyte.
Reverse Microemulsion Synthesis of Sulfur/Graphene Composite for Lithium/Sulfur Batteries
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Electrochemical Techniques for Intercalation Electrode Materials in Rechargeable Batteries
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Spinel LiNi 0.5 Mn 1.5 O 4 Cathode for High-Energy Aqueous Lithium-Ion Batteries
A 2.9 V intrinsic safe aqueous LiNi 0.5 Mn 1.5 O 4 /Mo 6 S 8 full cell delivers 80 W h kg -1 energy density with capacity decay of 0.075% per cycle (5 C). After the electrolyte pH value adjustment, almost full capacity of LiNi 0.5 Mn 1.5 O 4 (125 mA h kg -1 ) is achieved, and 126 W h kg -1 energy density is provided for LiNi 0.5 Mn 1.5 O 4 /Mo 6 S 8 cell, representing one of the highest voltage and energy density among all the aqueous batteries.
Tailoring Surface Acidity of Metal Oxide for Better Polysulfide Entrapment in Li‐S Batteries
The polysulfide shuttle reaction has severely limited practical applications of Li‐S batteries. Recently, functional materials that can chemically adsorb polysulfide show significant enhancement in cycling stability and Coulombic efficiency. However, the mechanism of the chemisorption and the control factors governing the chemisorption are still not fully understood. Here, it is demonstrated for the first time that the surface acidity of the host material plays a crucial role in the chemisorption of polysulfide. By tailoring the surface acidity of TiO 2 via heteroatom doping, the polysulfide‐TiO 2 interaction can be fortified and thus significantly the capacity fading be reduced to 0.04% per cycle. The discovery presented here sheds light on the mechanism of this interfacial phenomenon, and opens a new avenue that can lead to a practical sulfur/host composite cathode.
A Rechargeable Al/S Battery with an Ionic‐Liquid Electrolyte
Abstract Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite‐free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg −1 ) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x . Herein, we demonstrate the first reversible Al/S battery in ionic‐liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid‐state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid‐state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.
A Rechargeable Al/S Battery with an Ionic‐Liquid Electrolyte
Abstract Aluminum metal is a promising anode material for next generation rechargeable batteries owing to its abundance, potentially dendrite‐free deposition, and high capacity. The rechargeable aluminum/sulfur (Al/S) battery is of great interest owing to its high energy density (1340 Wh kg −1 ) and low cost. However, Al/S chemistry suffers poor reversibility owing to the difficulty of oxidizing AlS x . Herein, we demonstrate the first reversible Al/S battery in ionic‐liquid electrolyte with an activated carbon cloth/sulfur composite cathode. Electrochemical, spectroscopic, and microscopic results suggest that sulfur undergoes a solid‐state conversion reaction in the electrolyte. Kinetics analysis identifies that the slow solid‐state sulfur conversion reaction causes large voltage hysteresis and limits the energy efficiency of the system.