Japan researchers develop two new lithium superionic conductors for high-performance solid-state batteries
Researchers at the Tokyo Institute of Technology, in collaboration with colleagues from Toyota Motor Corporation, Tokyo Institute of Technology and High Energy Accelerator Research Organization Japan (KEK), have successfully designed and tested novel, high-power all-solid-state batteries with promising results.
The scientists synthesized two crystal materials that show great promise as lithium superionic conductors for use as solid electrolytes for Li-ion batteries. The materials, reported in a paper in the journal Nature Energy, feature an exceptionally high conductivity (25 mS cm−1 for Li9.54Si1.74P1.44S11.7Cl0.3), as well as high stability ( ∼0 V versus Li metal for Li9.6P3S12).
Two cells based on the novel solid electrolytes performed very well in trials in comparison with lithium-ion batteries. The cells remained stable and operated consistently at a range of temperatures between -30 and 100 °C. They exhibited high energy and high power densities, and very small internal resistance levels. Their properties would allow the cells to be stacked close together without interference.
Further, the cells exhibited ultrafast charging, retained their charge for lengthy periods, and appeared to have a long lifespan with excellent cycling ability (after over 500 cycles, the cells retained around 75% of their initial discharge capacity).
Most traditional batteries rely on the flow of ions through a liquid electrolyte between two electrodes. However, batteries incorporating a liquid electrolyte are prone to problems, including low charge retention and difficulties in operating at high and low temperature. Previous designs for solid electrolytes have shown promise, but have proven expensive and some have exhibited problems with electrochemical stability.
Compared with lithium-ion batteries with liquid electrolytes, all-solid-state batteries offer an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Despite extensive research efforts, the development of all-solid-state batteries still falls short of expectation largely because of the lack of suitable candidate materials for the electrolyte required for practical applications.—Kato et al.
Yuki Kato and his team synthesized two new lithium-based superionic materials based on a crystal structure previously discovered by the same team. They studied these crystal structures using Synchrotron X-ray diffractometer, BL02B2, at SPring-8 and neutron diffractometer iMATERIA(BL20) at J-PARC.
Superionic materials are solid crystal structures through which ions can hop easily, essentially maintaining a flow of ions similar to that which occurs inside a liquid electrolyte.
Both superionic materials developed by the team showed extremely high ionic conductivity and high stability. The researchers used their two new solid electrolytes to create two battery cell types; one high-voltage cell and one cell designed to work under large currents. Both all-solid-state cell types exhibited superior performance compared with lithium ion batteries. Kato’s team found that the cells provided high power density, with ultrafast charging capabilities and a longer lifespan than existing battery types.
Although the technology requires further development before it is commercially available, these results indicate that all-solid-state batteries may soon provide a much-needed boost to applications requiring stable, long-life energy storage, such as electric vehicles.
The addition of high energy electrodes into the solid-state cells could enhance the power of the batteries still further. Also, processing technology to complement the batteries that would allow for battery stacking is required before such configurations could be fully tested. Kato and his team are hopeful that their new materials will pave the way for all-solid-state batteries for multiple applications, including long-distance electric vehicles, in future.
This research is partially supported by New Energy and Industrial Technology Development Organization, Japan (NEDO).
Yuki Kato, Satoshi Hori, Toshiya Saito, Kota Suzuki, Masaaki Hirayama, Akio Mitsui, Masao Yonemura, Hideki Iba & Ryoji Kanno (2016) “High-power all-solid-state batteries using sulfide superionic conductors” Nature Energy Article number: 16030 doi: 10.1038/nenergy.2016.30