Room-temperature sodium-sulfur battery electrochemical based on limited sulfur molecules

In recent years, researchers at the Key Laboratory of Molecular Nanostructures and Nanotechnology Institute of the Institute of Chemistry, Chinese Academy of Sciences have systematically studied the electrochemical properties of chalcogens (S, Se) and their applications in lithium secondary batteries. In previous studies, they proposed the use of chain-like small sulfur molecules limited by carbon nanopores to solve the problem of the dissolution of polysulfides in lithium-sulfur batteries and to develop lithium-sulfur batteries with long cycle life (J. Am. Chem. Soc. ,2012,134,18510−18513); and successfully extended the idea of ​​the nanopore limited domain chain molecule to the selenium cathode, developed a new type of high volume energy density lithium-selenium battery (Angew.Chem.Int.Ed., 2013 ,52,8363−8367); In response to the journal "German Applied Chemistry", invited the author to write a review paper on lithium-sulfur batteries (Angew.Chem.Int.Ed., 2013, 52, 13186-13200).

Recently, under the support of the National Natural Science Foundation of China, the Ministry of Science and Technology, and the Chinese Academy of Sciences, researchers from the Key Laboratory of Molecular Nanostructure and Nanotechnology Institute of the Institute of Chemistry have made new progress in the research of novel high specific energy room temperature sodium-sulfur batteries. . The results of the study were published in the recently published Adv. Mater. (2014, 26, 1261−1265) and selected as the Back Cover paper.

The sodium-sulfur battery is a type of metal secondary battery in which the elemental sulfur is used as a positive electrode and the metallic sodium is used as a negative electrode to convert chemical energy and electric energy to each other through an electrochemical reaction between sulfur and sodium. Similar to the lithium-sulfur battery, the positive (S) and negative (Na) of the sodium-sulfur battery also have a high theoretical specific capacity, making the specific energy much higher than that of currently widely used lithium-ion batteries in smart grids, etc. The energy field has application potential.

However, due to the use of ceramic electrolytes, traditional sodium-sulfur batteries need to work at 300oC or higher, which presents potential safety hazards. In addition, during the discharge process, the reduction of sulfur is not complete, and only Na2S3 can be generated (Na2S should be generated when complete reduction), which decreases the capacity of the positive electrode material and the specific energy of the battery. The room-temperature sodium-sulfur battery based on the liquid electrolyte is limited by the disadvantages of low electrochemical activity of the sulfur cathode, easy dissolution of the discharge intermediate product in the electrolyte, and problems such as low utilization of positive electrode active material and poor cycle performance, which seriously affect the battery Performance and practical application.

In view of the similarities between lithium-sulfur batteries and room-temperature sodium-sulfur batteries, researchers at the Institute of Chemistry have pioneered the application of small sulfur molecules in sodium-sulfur batteries and the assembly of room temperature with sodium negative electrodes and carbonate electrolytes. The prototype battery that can work.

Since the chain-like small sulfur molecule has very high sodium-to-sodium electrochemical activity at room temperature, it can be completely reduced to Na2S during the discharge process, thereby making its discharge capacity based on the sulfur mass calculation of the cathode first cycle as high as 1610 mAhg-1, which is a traditional high temperature Three times the theoretical capacity of a sulfur cathode material in a sodium-sulfur battery. Based on electrode material calculations, the first cycle of sodium-sulfur battery discharge energy ratio can be as high as 955Whkg-1, after 200 cycles can still be stable at about 750Whkg-1. In addition, the room temperature sodium-sulfur battery also has good rate and cycle performance.

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