Simple Method Stabilizes Li-Ion Conductor

Lithium-ion batteries are the rechargeable workhorses that power the great majority of today’s electricity-hungry portable gadgets and tools. These batteries boast extreme reliability and an outstanding performance record. Nonetheless, the cells’ flammable liquid organic electrolyte solution poses a minute but potentially serious safety hazard. Researchers have tried for years to develop a solid-state nonflammable replacement for the liquid electrolyte, but most of the solids are weak Li-ion conductors. Tohoku University materials scientist Hitoshi Takamura and coworkers showed several years ago that at high temperature, a structural transition causes the conductivity of LiBH₄ to jump by three orders of magnitude compared with the room-temperature value. A related phase transition causes LiBH₄ to conduct strongly at high pressure. But it is difficult to keep these phases stable under ambient conditions. Now, on the basis of X-ray, microscopy, and conductivity analyses, the Tohoku team has shown that intimately mixing LiBH₄ and potassium iodide and sintering the solid solution in vacuum at about 200 °C forms a highly conducting phase that remains stable at ambient conditions (APL Mater. 2014, DOI: 10.1063/1.4876638 ).