Japanese researchers have discovered a new type of lithium ion conductor that can be used to develop solid state lithium ion batteries – a major breakthrough that could improve safety of battery-powered devices.
The team from Tohoku University, Japan, used lithium borohydride, which has been considered for use in lithium ion batteries before, but was ruled out as it requires very high pressure and temperature to remain stable.
However, the Japanese team has managed to figure out a method which allows using lithium borohydride (LiBH4) at room temperature and normal atmospheric pressure.
In a study published in the journal APL Materials, the researchers describe how they doped a cubic lattice of KI molecules with the LiBH4. This allowed them to stabilize the high-pressure form of lithium borohydride and make a solid solution at normal atmospheric pressure that was stable at room temperature.
The team discovered that the Li+ ions functioned like pure Li+ ion conductors, even though they were just doping the KI lattices. This is the reverse of the normal doping technique, in which a small amount of stabilizing element would be added to an ionic conductor abundant in lithium.
"In other words, LiBH4 is a sort of 'parasite' but not a host material," said Hitoshi Takamura who led the research at Tohoku University. He and his colleagues have called this mechanism "parasitic conduction" and have suggested that it could be broadly applied in the search for new batteries as small amounts of Li+ ions could be used to dope an oxide, sulfide, halide or nitride host material.
"This work suggests the potential of this mechanism in the ongoing search for the perfect material for use in solid state batteries," Takamura said. "The urgency of this quest has been abundantly clear after the grounding of so many aircraft in recent months."
The lithium ion batteries, having very good durability, are used in most electronic gadgets today, including implantable medical devices and wearable consumer electronics. However, the use of liquid chemicals involving lithium salts dissolved in organic solvents makes those batteries prone to a fire risk. Such a risk would be eliminated if the cells were completely solid-state. Thus the discovery of a solid state conductor could become a game-changer in the industry.