Bi-functional electrolyte promises longer-life batteries

In a study published in the Journal of the American Chemical Society, ORNL researchers are said to have challenged a long-held assumption that a battery’s positive cathode, negative anode and ion-conducting electrolyte can play only one role in the device.

The electrolyte in the team’s new battery design serves as an ion conductor and also as a cathode supplement. This cooperative chemistry, enabled by the use of an ORNL-developed solid electrolyte, is claimed to deliver an extra boost to the battery’s capacity and extends the lifespan of the device.

’This bi-functional electrolyte revolutionizes the concept of conventional batteries and opens a new avenue for the design of batteries with unprecedented energy density,’ said ORNL’s Chengdu Liang.

According to ORNL, the team demonstrated the new concept in a lithium carbon fluoride battery, considered one of the best single-use batteries because of its high energy density, stability and long shelf life.

When ORNL researchers incorporated a solid lithium thiophosphate electrolyte, the battery generated a 26 per cent higher capacity than what would be its theoretical maximum if each component acted independently. The increase, Liang said in a statement, is caused by the cooperative interactions between the electrolyte and cathode.

‘As the battery discharges, it generates a lithium fluoride salt that further catalyses the electrochemical activity of the electrolyte,’ Liang said. ‘This relationship converts the electrolyte - conventionally an inactive component in capacity - to an active one.’

The improvement in capacity could translate into years or even decades of extra life, depending on how the battery is engineered and used. Longer-lived disposable batteries are in demand for applications such as such as artificial cardiac pacemakers, RFID devices, remote keyless system, and sensors, where replacing or recharging a battery is not possible or desirable.

‘If you have a pacemaker, you don’t want to undergo surgery every 10 years to replace the battery,’ Liang said. ‘What if a battery could last 30 to 50 years? Our fundamental research is opening up that possibility through a new design mechanism.’

The study is published as “Pushing the Theoretical Limit of Li-CFx Batteries: A Tale of Bi-functional Electrolyte.” Co-authors are ORNL’s Ezhiylmurugan Rangasamy, Juchuan Li, Gayatri Sahu, Nancy Dudney and Chengdu Liang. The work was sponsored by the Division of Materials Sciences and Engineering in DOE’s Office of Science.