The relatively long life of lithium ion batteries makes them the rechargeable choice for a wide range of devices. Nevertheless, lithium ion batteries rely on liquid chemistries involving lithium salts dissolved in organic solvents, creating flame risks that would be avoided if the cells were completely solid-state.
Recently, a team of researchers at Tohoku University in Japan managed to create a new type of lithium ion conductor that could serve as the basis for an entirely new generation of solid-state batteries.
Essentially, the connector uses rock salt Lithium Borohydride (LiBH4), a well-known agent in organic chemistry laboratories that has been considered for batteries before, but up to now has only worked at high temperatures or pressures.
In the journal APL Materials, the researchers describe how they doped a cubic lattice of KI molecules with the LiBH4. This allowed the team to stabilize the high-pressure form of Lithium borohydride, effectively creating a solid solution at normal atmospheric pressure that was stable at room temperature.
During the process, the team made the peculiar discovery 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,” explained Hitoshi Takamura who led the research at Tohoku University. He and his colleagues have dubbed this mechanism “parasitic conduction,” suggesting that it could be broadly applied in the search for new batteries – anywhere that 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. The urgency of this quest has been abundantly clear after the grounding of so many aircraft in recent months,” Takamura added.