With the vigorous development of electric vehicles, portable electronic devices and household energy storage power sources, there is an urgent need to develop high specific energy secondary battery systems. Lithium-sulfur batteries have become the research frontier and hotspot in the field because of their theoretical mass-specific energy of up to 2600 Wh/kg.
Recently, under the strong support of the Chinese Academy of Sciences' Pilot Specialization, the Ministry of Science and Technology, the National Natural Science Foundation of China, and the Chinese Academy of Sciences, Guo Yuguo, a researcher in the Key Laboratory of Molecular Nanostructures and Nanotechnology Institute of the Institute of Chemistry, Chinese Academy of Sciences, has been a researcher in the metal lithium negative electrode. Sulfur-related positive basic research, and lithium-sulfur soft pack battery engineering technology research and development made a series of progress (J. Am. Chem. Soc., 2012, 134, 18510; Angew. Chem. Int. Ed., 2013, 52, 13186; J. Am. Chem. Soc., 2015, 137, 2215; Nat. Commun., 2015, 6: 8058, doi:10.1038/ncomms9058).
The researchers of this research group have long been dedicated to the research of highly efficient and stable high specific energy lithium-sulfur battery materials. In the previous research work, they focused on the problem of the formation of easily soluble polysulfide ions in the charge-discharge process of conventional cyclic S8 positive electrode materials in lithium-sulfur batteries, resulting in poor cycling performance of sulfur positive electrodes. The chain-like small sulfur molecule fundamentally solves the new idea of ​​the dissolution problem of this polysulfide ion, and achieves the screening and stabilization of unconventional and metastable small sulfur molecules through the spatial confinement effect of nanochannels, and the specific capacity is prepared. High-rate, high-rate sulfur carbon cathode materials with excellent cycle performance (J. Am. Chem. Soc., 2012, 134, 18510). Recently, they have made new progress in the study of the mechanism of electrochemical lithiation/delithiation reaction of space-bound chain sulfur molecules. The results of the research are published in the recent J. Am. Chem. Soc. (2015, 137, 2215− 2218) Magazine.
They limited the one-dimensional chain-like sulfur molecules to the carbon nanotubes and succeeded in producing a model system for studying the electrochemical properties of chain-like sulfur molecules. Through systematic in-situ and semi-in-situ studies, it has been found that carbon nanotube-limited chain sulfur undergoes a novel electrochemical reaction process, the sulfur chain is shortened in the reaction, the electrochemical performance is spontaneously optimized, and the reaction is close to solid Instead, it effectively avoids the dissolution of the sulfur cathode intermediate product (Figure 1). On the basis of revealing the intrinsic mechanism of its cycle stability, they proposed a rational design scheme for high-efficiency and stable high-capacity sulfur-carbon composite cathode materials using a "bifunctional core-shell structure dielectric-microporous carbon support". Through this program, both the sulfur loading capacity and the polysulfide dissolution are effectively limited, and a technical solution for the preparation of sulfur cathode materials that can be scaled up is realized.
In addition to the sulfur cathode, metal lithium cathode is also the key to the practical application of lithium-sulfur batteries. In response to the problem of uneven dissolution and deposition (ie, dendrite) of metallic lithium negative electrodes during charge and discharge, they proposed the idea of ​​using three-dimensional nano copper current collectors to guide the uniform deposition and dissolution of metallic lithium inside the three-dimensional electrodes, and successfully achieved the negative electrode surface. Lithium metal dendrite control. The results were recently published in the magazine Nat. Commun. (2015, 6, 8058).
Studies have shown that when a three-dimensional copper foil with submicron framework and high specific surface area is used for the deposition of metallic lithium, the lithium negative electrode is mainly deposited in the pores of the three-dimensional copper foil (>98%), and the growth of lithium dendrites on the electrode surface is obtained. Effective suppression (Figure 2). Compared to the lithium negative electrode on the flat copper current collector, the metal lithium negative electrode confined in the three-dimensional nano copper current collector can continuously work for more than several hundred hours without short-circuiting, and the deposition efficiency of lithium is greatly improved; the life and stability of the battery and Security has also been significantly improved. This discovery reveals the role of lithium negative current collectors, and has important guiding significance for designing practical lithium negative electrodes.
Based on the above basic research, the researchers also focused on lithium-sulfur battery engineering technology research and development. Under the support of the long-term pilot-powered battery, a strategic pilot technology project of the Chinese Academy of Sciences under the “Transformative Nanofabrication Industry Technology Focus†project, a lithium-sulfur soft pack battery assembly line was established at the Institute of Chemistry, and various performances of lithium-sulfur soft pack batteries were established. The indicators have made important progress. At present, lithium sulfur soft batteries with different capacities of 0.5-30 Ah can be prepared in batches with an energy density of 350-450 Wh/kg and a cycle time of more than 50 cycles. The relevant lithium sulfur soft pack battery was exhibited at the 6th China International Nanotechnology Conference (ChinaNANO 2015) held in Beijing from September 3rd to 5th (Figure 3).
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