Researchers at the University of Western Ontario are proposing selenium (Se) as a promising cathode material for all-solid-state Li batteries, paired with a lithium-tin (L-Sn) alloy as an anode and Li3PS4 as the electrolyte.
In a paper in the RSC journal Energy & Environmental Science, the team reports that in addition to the high electronic conductivity (1×10-3 S cm-1) of Se, a high Li+ conductivity of 1.4×10-5 S cm-1 across the Se-Li3PS4 interface can be achieved. The all-solid-state Li-Se cell shows a high reversible capacity of 652 mAh g-1 (96% of theoretical capacity) and exhibits favorable capacity retention upon cycling.
|(a) Schematic diagram of an all-solid-state Li-Se battery. (b) Typical discharge/charge profiles of Se and S cathodes in all-solid-state batteries at 50 mA g-1 at room temperature. Li et al. Click to enlarge.|
Since the 2000s, all-solid-state Li-S batteries have been studied as a promising alternative battery system due to the high theoretical energy densities (2567 Wh/kg compared to 387 Wh/kg for LIBs). However, these systems are still confronted with major challenges in terms of rechargeability, cycling stability, Coulombic efficiency and rate performance, which are far from commercialization. The fatal weaknesses of all-solid-state Li-S batteries are poor Li+ and electron transports between the electrode and the electrolyte.
Unlike batteries with liquid electrolytes that can easily wet the electrodes and ensure smooth Li+ transport, the Li+ transport in solid-state batteries is highly limited at the electrode-electrolyte interface. Although many of sulfide-based solid-state electrolytes exhibit high Li+ conductivities (10-4 to 10-2 S cm-1 at room temperature), the Li+ transport through the interface can be lagged by several orders of magnitude. … Meanwhile, the poor electronic conductivity of S cathodes is hindering the solid-state electrochemical reactions (lithiation/delithiation). In addition to engineering the S cathodes for all-solid-state batteries, developing new cathode materials with high ionic and electronic conductivities is another important approach to realize all-solid-state lithium batteries.
Compared to S, Se has much higher electronic conductivity (1×10-3 vs. 0.5×10-27 S m-1 at room temperature). Herein, an all-solid-state Li-Se battery is developed for the first time.—Li et al.
The reversible charge capacity of the Li-Se cell (643 mAh g-1) was substantially higher than that of a Li-S cell (527 mAh g-1). Moreover, the team found, the Li-Se cell exhibited a significantly smaller polarization than the Li-S cell, indicating a higher energy efficiency and a more feasible electrochemical process of Se than S.
Based on their results, the team suggests that compositing Se and S for an advanced hybrid cathode could be a new strategy for enabling high-performance all-solid-state Li batteries. Fine tuning the balance between the ionic and electronic conductive Se and the high capacity S is currently under investigation.
The work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Research Chair Program (CRC), China Automotive Battery Research Institute, Canada Foundation for Innovation (CFI), and University of Western Ontario.
Xiaona Li, Jianwen Liang, Xia Li, Changhong Wang, Jing Luo, Ruying Li and Xueliang Sun (2018) “High-performance All-Solid-State Li-Se Batteries Induced by Sulfide Electrolyte” Energy & Environmental Science doi: 10.1039/C8EE01621F