Xiamen University JACS: lithium-sulfur battery cathode materials based on cluster molecules

introduction

At present, lithium-ion batteries are widely used in various portable electronic devices and electric vehicles. However, with the continuous development of these devices, lithium-ion batteries are gradually unable to meet the development needs of the society. In order to further expand the application prospects of lithium-ion batteries, various systems of batteries have attracted the attention of researchers. Among them, lithium-sulfur batteries are receiving increasing attention. A lithium-sulfur battery is a lithium battery in which sulfur element is used as a positive electrode material and metal lithium is used as a negative electrode material. Elemental sulfur is abundant in the earth, with low price and environmental friendliness. Lithium-sulfur batteries using sulfur as a positive electrode material have higher theoretical specific capacities and theoretical specific energy of batteries, reaching 1675m Ah/g and 2600Wh/kg, respectively, which is almost the theoretical ratio of conventional positive electrode materials such as transition metal oxides and phosphate materials. 10 times the capacity; In addition, sulfur also has the advantages of low price, environmental friendliness, etc. It is a very promising lithium battery.

Achievements

Recently, Prof. Dong Quanfeng from School of Chemistry and Chemical Engineering of Xiamen University and Professor Leroy Cronin from the University of Glasgow in the United Kingdom have made new progress in the research of lithium-sulfur batteries. Related results include "Strategies to Explore and Develop Reversible Redox Reactions of Li-S in Electrode Architectures using "Silver-Polyoxometalate Clusters" was published on JACS (DOI: 10.1021/jacs.8b0041). Prior to this, Prof. Dong Quanfeng's research group conducted a systematic study of lithium-sulfur battery sulfur composite cathode materials. The reaction mechanism of lithium-sulfur batteries was explored through in-situ Raman technology combined with theoretical calculations, confirming that the nitrogen-doped modification of the sulfur-bearing base material can achieve a complete charge-discharge cycle of elemental sulfur as the positive electrode active material (Chem. Mater., 2015, 27, 2048?2055); Afterwards, the Co-catalytic effect of Co-N was successfully applied to the redox process of S for the first time, and the concept of “multifunctional, dual catalytic” was proposed (EES, 2016, 9, 1998-2004); Based on the improvement of the sulfur content of the composite positive electrode material, the research team for the first time prepared non-carbon mesoporous Co4N microspheres and achieved a sulfur loading of up to 95% (ACS Nano, 2017, 11, 6031-6039).

Transition metal polyacid oxides (POMs) are a type of nanocluster material with a reversible multi-electron reaction characteristic, which is visually called an “electronic sponge” because it can reversibly store ions and electrons. The feasibility of having a higher specific energy storage material. In this study, for the first time, polyoxometalate molecular clusters were used as positive electrode materials for lithium-sulfur batteries. This material (K3[H3AgIPW11O39]) has both Lewis acid and Lewis base sites, and thus has the function of double-site adsorption of polysulfides. The efficient control of the sulfur electrochemical reaction process can be achieved. The experimental results and DFT theoretical calculations show that the Ag(I) heterometal ions in the framework structure of polyanion can regulate the adsorption of polysulfide in the whole system and the adsorption of lithium ions at the terminal oxygen atom. The lithium-sulfur battery prepared with it as a skeleton material exhibits excellent electrochemical performance.

Graphic guide

figure 1. POMs absorb Li2S produced by lithium-sulfur battery system

figure 2. Calculated Adsorption Gibbs Free Energy Difference (ΔGads) and Li2Sn (n=8,6,4) with PW12O40 and K3[H3AgIPW11O39] Clusters

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