Japanese researchers announced March 22, 2016, that they have developed an electrolyte having a lithium-ion (Li-ion) conductivity twice as high as before.

When they prototyped an "all-solid-state ceramic battery" by using the electrolyte, they found that its output characteristic is more than three times higher than that of existing Li-ion rechargeable batteries.

The researchers are from (1) a team led by Ryoji Kanno, professor at the Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, (2) Toyota Motor Corp, (3) High Energy Accelerator Research Organization (KEK), etc.

This time, the researchers developed two kinds of electrolytes, and they are both sulfide-based materials. The composition of one electrolyte is Li9.54Si1.74P1.44S11.7Cl0.3. Its Li-ion conductivity is 25mS/cm (temperature: 27°C), which is very high for a solid electrolyte. Before the development of this material, an LGPS (Li10GeP2S12)-based material that Kanno, etc developed in 2011 had the highest Li-ion conductivity (12m-14mS/cm) of all solid electrolytes.

The composition of the other electrolyte is Li9.6P3S12. Its Li-ion conductivity is about 1mS/cm (room temperature), which is equivalent to that of conventional materials. But it stably functions as an electrolyte for metal lithium, which is a promising negative electrode material candidate.

By using those materials, the researchers prototyped an all-solid-state ceramic battery and confirmed that its output density and energy density are more than three and two times, respectively, higher than those of conventional Li-ion batteries. Its output density is even equivalent to or higher than those of devices called "super-capacitor" and "electric double-layer capacitor," they said.

However, they did not disclose how the two kinds of ion-conductive materials are used, what are the positive- and negative-electrode materials or other details of the battery design.

In regard to the charge/discharge cycle characteristics of the prototyped battery, its capacity was hardly lowered between 200 to 1,000 cycles (temperature: -30 to 100°C). Especially, its charge/discharge efficiency (the ratio of charging capacity to discharge capacity for each cycle) was almost 100% even after 1,000 cycles, the researchers said.