Extremely fast ion conductors: Another step towards better beatteries

July 16, 2013 // By Christoph Hammerschmidt
Though they started their research on future battery materials only past April, they already have achieved potentially seminal results: A research team at the Technical University of Graz (Austria) succeeded in providing fundamental data on the nuclear dynamics of a specific ion conductor that could greatly improve the characteristics of lithium-ion batteries.

Not only the development electromobility but also the design of more powerful smartphones and portable computers pose high challenges to battery systems: Engineers and not least customers expect the energy storage to offer increased capacity and safety as well as better longevity. Towards this end, solid-state lithium batteries are among the white hopes of battery research. In comparison to conventional lithium-ion batteries with liquid electrolytes, solid-state batteries feature superior characteristics with respect to safety, service life and thermal stability. For this reason, scientists from disciplines such as solid-state chemistry, physics and materials sciences are searching feverishly for solid-state ion conductors suitable for use in such batteries.

In his dissertation work, Viktor Epp from the Institute of Chemical Technologies and Materials of the Graz Technical University scrutinized a specific sulphide: Li6PS5Br. He got granular on this material by submitting the material to lithium nuclear magnetic resonance spectroscopy and could solidify the results of earlier and more tentative works: The lithium ions in the sulphide at hand move incredibly fast. This qualifies the material as a front-runner among solid-state electrolytes for usage in batteries.

Epp observed more than a billion "ion jumps" per second at normal ambient temperature. This translates into enormous charge carrier mobility, one of the fundamental properties of a promising material.

Such a high carrier mobility has already been verified in other lithium-based chemical combinations. However, many of these materials are not only ion conductors but also electron conductors which disqualifies them for the use as solid-state electrolyte.

At first sight, the principle of electrochemical energy storage in a lithium-ion battery seems to be simple: During the process of charging and discharging a battery, the ions move between the battery poles and during this journey they cross materials which are different in structure. In a solid-state lithium-ion battery, a solid matter such as an oxide that contains lithium or a sulphide, assume the task of the conduction electrolyte. "The