Deyu Qu

Advanced Separators for Lithium‐Ion and Lithium–Sulfur Batteries: A Review of Recent Progress

Li-ion and Li-S batteries find enormous applications in different fields, such as electric vehicles and portable electronics. A separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of the separators directly influence the performance of the batteries. Traditional polyolefin separators showed low thermal stability, poor wettability toward the electrolyte, and inadequate barrier properties to polysulfides. To improve the performance and durability of Li-ion and Li-S batteries, development of advanced separators is required. In this review, we summarize recent progress on the fabrication and application of novel separators, including the functionalized polyolefin separator, polymeric separator, and ceramic separator, for Li-ion and Li-S batteries. The characteristics, advantages, and limitations of these separators are discussed. A brief outlook for the future directions of the research in the separators is also provided.

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.

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.

Self-assembly synthesis of a unique stable cocoon-like hematite @C nanoparticle and its application in lithium ion batteries

A novel cocoon-like Fe2O3@C nanoparticle was fabricated via a facile hydrothermally molecular self-assembly procedure. Compared to bare Fe2O3 nanoparticles, the carbon coated Fe2O3 nanoparticles exhibit higher specific capacity, excellent rate capacity and cyclic stability as the anode in lithium ion batteries. These cocoon-like Fe2O3@C nanoparticles carry enhanced lithium storage properties with a reversible capacity of 358mAhg-1 after 150 cycles under the current density of 1000mAg-1, while the carbon-free bare Fe2O3 can only deliver a much lower capacity of 127.6mAhg-1 with a continuously decreasing trend. The excellent performance of Fe2O3@C is attributed to the coated carbon layers, which not only enhance the electronic conductivity but also reduce the stress upon the Fe2O3 nanoparticles caused by the volume change during the charge/discharge process.

High-Capacity and Self-Stabilized Manganese Carbonate Microspheres as Anode Material for Lithium-Ion Batteries

Manganese carbonate (MnCO3) is an attractive anode material with high capacity based on conversion reaction for lithium-ion batteries (LIBs), but its application is mainly hindered by poor cycling performance. Building nanostructures/porous structures and nanocomposites has been demonstrated as an effective strategy to buffer the volume changes and maintain the electrode integrity for long-term cycling. It is widely believed that microsized MnCO3 is not suitable for use as anode material for LIBs because of its poor conductivity and the absence of nanostructure. Herein, different from previous reports, spherical MnCO3 with the mean diameters of 6.9 μm (MnCO3-B), 4.0 μm (MnCO3-M), and 2.6 μm (MnCO3-S) were prepared via controllable precipitation and utilized as anode materials for LIBs. It is interesting that the as-prepared MnCO3 microspheres demonstrate both high capacity and excellent cycling performance comparable to their reported nanosized counterparts. MnCO3-B, MnCO3-M, and MnCO3-S deliver reversible specific capacities of 487.3, 573.9, and 656.8 mA h g(-1) after 100 cycles, respectively. All the MnCO3 microspheres show capacity retention more than 90% after the initial stage. The advantages of MnCO3 microspheres were investigated via constant-current charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that there should be substantial structure transformation from microsized particle to self-stabilized nanostructured matrix for MnCO3 at the initial charge/discharge stage. The evolution of EIS during charge/discharge clearly indicates the formation and stabilization of the nanostructured matrix. The self-stabilized porous matrix maintains the electrode structure to deliver excellent cycling performance, and contributes extra capacity beyond conversion reaction.

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.

Electrochemical Hydrogen Storage in a Highly Ordered Mesoporous Carbon

A highly order mesoporous carbon has been synthesized through a strongly acidic, aqueous cooperative assembly route. The structure and morphology of the carbon material were investigated using TEM, SEM and nitrogen adsorption-desorption isotherms. The carbon was proven to be meso-structural and consisted of graphitic micro-domain with larger interlayer space. AC impedance and electrochemical measurements reveal that the synthesized highly ordered mesoporous carbon exhibits a promoted electrochemical hydrogen insertion process and improved capacitance and hydrogen storage stability. The meso-structure and enlarged interlayer distance within the highly ordered mesoporous carbon are suggested as possible causes for the enhancement in hydrogen storage. Both hydrogen capacity in the carbon and mass diffusion within the matrix were improved.

A new perspective on the 5 V discharge capacity of Li/Al doped manganese spinels

A series of manganese spinels LiMn2−yMeyO4 (Me = Li, Al, Mg) were prepared and examined by XRD and electrochemical methods. The spinels doped with Li or high content of Al can exhibit discharge capacity in the 5 V region, but spinels doped with Mg do not exhibit any 5 V discharge capacity. It is also observed that the 5 V discharge capacity of Li/Al doped spinels will be greatly suppressed once calcinated at temperatures above 900 °C in preparation. It is suggested that the 5 V discharge capacity of Li/Al doped spinels may be originated from the special chemical/structural characteristics of spinel phases containing Li or high content of Al prepared at temperatures below 900 °C.

The effects of structural properties on the lithium storage behavior of mesoporous TiO2

Understanding the effects of structural properties on the lithium storage behavior of mesoporous TiO2 is crucial for further optimizing its performance through rational structure design. To achieve this, herein, the surface area and the grain size of the prepared mesoporous TiO2 are intentionally adjusted by controlling the calcination temperatures. It is found that the capacities of the mesoporous TiO2 contain both the lithium-ion insertion into the bulk phase (Q in) and the additional surface lithium storage (Q as). The Q in gradually increases with grain sizes to a steady level and then slightly drops. By contrast, the Q as is directly proportional to the specific surface area of the mesoporous TiO2 and is ascribed to the capacity originated from the lithium-ion insertion into the surface layer. The experimental comparison and analysis demonstrate that the fast kinetics of the Q as ensure both the better rate performance and capacity retention of mesoporous TiO2 than bulk ones. Specially, the mesoporous TiO2 calcinated at 350 °C shows the highest reversible specific capacity of 250.2 mA h g-1, the best rate capability (132.5 mA h g-1 at 2C) and good cycling stability. Our findings shed great light on the design of high-performance nanostructured TiO2 with surface lithium storage.

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.