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German scientists have developed a solid-state lithium-sulfur battery with excellent performance

2020-02-25
With the development of the automobile industry, people are vigorously pursuing energy storage systems with higher energy density, more top safety factors, and lower costs. Lithium-sulfur batteries (Li-S) are considered to be very promising, which is more than four times higher than the theoretical energy density (606Wh kg-1) of the lithium-ion battery calculated based on the theoretical capacity of 279 mAh g-1 of LiNi0.8Co0.15Al0.05O2. However, its practical application has been severely challenged by low-sulfur active material utilization, polysulfide shuttle effects, and the limitations of lithium dendrite growth in lithium anodes.
Solid-state lithium-sulfur batteries (SSLSB) are getting more and more attention, mainly because it can inhibit the growth of lithium dendrites and have a considerable energy density, and has great potential in solving safety issues. Also, the polysulfide shuttle effect of positive sulfur electrodes can be explained in solid-state batteries.
On February 21, 2020, Peter Bieker (corresponding author) of the MEET Battery Research Center at the University of Münster, Germany, published on Adv. Funct. Mater. "Solid-State Lithium-Sulfur Battery Enabled by Thio-LiSICON / PolymerComposite Electrolyte and Sulfurized "Polyacrylonitrile Cathode," the paper states that a new SSLSB structure, as shown in Figure 1c, introducing a Li3.25Ge0.25P0.75S4 (LGPS) / polyethylene oxide (PEO) composite electrolyte (LCE) to replace the conventional hard Inorganic solid electrolyte. The purpose is to improve the wettability of the stable electrolyte interface and reduce the charge transfer resistance. S / PAN is used as a positive electrode material because of its unique electrochemical properties: electrochemical and structural studies combining nuclear magnetic resonance and electron paramagnetic resonance characterization reveal the charge/discharge mechanism of S / PAN, which is a sulfur-grafted conjugated polymer The free-radical-mediated redox reaction in the framework of the material, this characteristic of S / PAN helps to alleviate the volume change of the positive electrode and maintain rapid redox kinetics, thus replacing the traditional S / C positive electrode.
 
Figure 1. Comparison of the structure of (a) a liquid S-Li battery, (b) a conventional solid-state S-Li battery, and (c) a solid-state Li-S battery proposed in this paper.
 
Figure 2. Schematic diagram and corresponding characterization of LGPS / PEO composite electrolyte (LCE) preparation process
The assembled SSLSB full battery showed excellent performance of 1183 mAh g-1 and 719 mAh g-1 at 0.2C and 0.5 C, respectively, and could still maintain 588 mAh g-1 after cycling 50 cycles at 0.1 C Capacity. At the same time, combined with mechanical and structural studies, the free radical participation mechanism of S / PAN was revealed, and the superior properties of this new SSLSB were explained from the more basic electrochemical characteristics of S / PAN.
 
Figure 3. Ionic conductivity and migration number of LCE
 
Figure 4. Schematic and corresponding electrochemical performance of Li-Li symmetrical battery
 
Figure 5. Cycle performance of S / PAN / LCE \ Li full battery at 0.1 C and 60 ° C
The author uses the advantages of both LCE and S / PAN positive electrodes to develop a high-performance solid-state lithium-sulfur battery. The prepared LCE has high ion conductivity (0.42 × 10-3S cm-1) and lithium-ion migration number (0.87). At the same time, it has an excellent electrochemical performance. The flexible structural design makes the solid-state lithium-sulfur battery successful and provides new ideas for the future design of solid-state lithium-sulfur batteries with excellent performance.