Zhong Ma

A review of cathode materials and structures for rechargeable lithium–air batteries

Rechargeable lithium air (Li–air) batteries, especially the non-aqueous type, are considered the most promising energy storage and conversion device candidates for use in future electric vehicle applications due to their ultrahigh energy density. The air cathode has been identified as a key factor affecting the overall performance of Li–air batteries. The current low level performance of air cathodes is the major challenge hindering commercial applications of Li–air batteries. In the past decade, a great many cathode materials, structures and fabrication processes have been developed and investigated with the goal of enhancing cathode performance. This paper reviews, the role of the cathode in non-aqueous Li–air batteries including the cathode reaction mechanisms and the properties and morphologies of cathode materials, followed by approaches to optimize cathode performance. The most recently published global progress and the main achievements in the field of Li–air batteries are also systematically and critically reviewed in terms of cathode materials, structures and fabrication processes, with the objective of providing some state-of-the-art information. Technical challenges are analyzed, and insights into future research directions for overcoming these development challenges of rechargeable non-aqueous Li–air battery cathodes are also identified in this review paper.

Synthesis of a Series of Fluorinated Boronate Compounds and Their Use as Additives in Lithium Battery Electrolytes

A new series of anion receptors based on boronate compounds have been synthesized. These compounds can be used as anion receptors in lithium battery electrolytes. The so-called boronate means that the compounds contain a boron bonded with two oxygen atoms and one carbon atom. This series includes various boronate compounds with different fluorinated aryl and fluorinated alkyl groups. When these anion receptors are used as additives in 1,2-dimethoxyethane (DME) solutions containing various lithium salts, the ionic conductivities of these solutions are greatly increased. The electrolytes tested in this study were DME solutions containing the following lithium salts: LiF, CF 3 COOLi, and C 2 F 5 COOLi. Without the additive, the solubility of LiF in DME (and all other nonaqueous solvents) is very low. With some of these boronate compounds as additives, LiF solutions in DME with concentration as high as 1 M were obtained. The solubilities of the other salts were also increased by these additives. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy studies show that I - anions are complexed with these compounds in DME solutions containing LiI salts. The degree of complexation is also closely related to the structures of the fluorinated aryl and alkyl groups which act as electron-withdrawing groups. The NEXAFS results are in good agreement with ionic conductivity studies.

Novel Flower-like Nickel Sulfide as an Efficient Electrocatalyst for Non-aqueous Lithium-Air Batteries

In this paper, metal sulfide materials have been explored for the first time as a new choice of bifunctional cathode electrocatalyst materials for non-aqueous lithium-air batteries (LABs). Nickel sulfides with two different morphologies of flower-like (f-NiS) and rod-like (r-NiS) are successfully synthesized using a hydrothermal method with and without the assistance of cetyltrimethyl ammonium bromide. As LAB cathode catalysts, both f-NiS and r-NiS demonstrate excellent catalytic activities towards the formation and decomposition of Li2O2, resulting in improved specific capacity, reduced overpotentials and enhanced cycling performance when compared to those of pure Super P based electrode. Moreover, the morphology of NiS materials can greatly affect LAB performance. Particularly, the f-NiS is more favorable than r-NiS in terms of their application in LABs. When compared to both r-NiS and pure super P materials as LAB cathode materials, this f-NiS catalyst material can give the highest capacity of 6733 mA h g−1 and the lowest charge voltage of 4.24 V at the current density of 75 mA g−1 and also exhibit an quite stable cycling performance.

Novel nanowire-structured polypyrrole-cobalt composite as efficient catalyst for oxygen reduction reaction

A novel nanowire-structured polypyrrole-cobalt composite, PPy-CTAB-Co, is successfully synthesized with a surfactant of cetyltrimethylammounium bromide (CTAB). As an electro-catalyst towards oxygen reduction reaction (ORR) in alkaline media, this PPy-CTAB-Co demonstrates a superior ORR performance when compared to that of granular PPy-Co catalyst and also a much better durability than the commercial 20 wt% Pt/C catalyst. Physiochemical characterization indicates that the enhanced ORR performance of the nanowire PPy-CTAB-Co can be attributed to the high quantity of Co-pyridinic-N groups as ORR active sites and its large specific surface area which allows to expose more active sites for facilitating oxygen reduction reaction. It is expected this PPy-CTAB-Co would be a good candidate for alkaline fuel cell cathode catalyst.