Researchers improve stability in lithium–oxygen batteries

Researchers from the University of Liverpool and Loughborough University have been working with British company Johnson Matthey — a developer of sustainable technologies — to create stable and practical electrolytes for lithium–oxygen (Li–O₂) batteries.

The lithium–oxygen (or lithium–air) battery, consisting of lithium metal and a porous conductive framework as its electrode, releases energy from the reaction of oxygen from the air and lithium. The technology is currently in its infancy, but in theory could provide much greater energy storage than the conventional lithium-ion battery.

In a new paper, published in the journal Advanced Functional Materials, the team has designed a blend of materials that are stable with a lithium metal anode — the negative part of a cell. And while work still needs to be done to improve the stability of materials at the cathode (the positive part), the breakthrough marks a significant milestone in the future of energy storage, with Li–O₂ cells expected to have up to 10 times the charge capacity of current batteries.

Professor Laurence Hardwick from the University of Liverpool’s Stephenson Institute for Renewable Energy (SIRE) and colleagues meticulously characterised and developed electrolyte formulations that significantly minimise side reactions within the battery to enable improved longer cycle stability. According to lead author Dr Alex Neale, who is also with SIRE, the research demonstrates that the reactivity of certain electrolyte components can be switched off by precise control of component ratios.

“The ability to precisely formulate the electrolyte using readily available, low-volatility components enabled us to specially tailor an electrolyte for the needs of metal–air battery technology that delivered greatly improved cycle stability and functionality,” Dr Neale said.

“The outcomes from our study really show that by understanding the precise coordination environment of the lithium ion within our electrolytes, we can link this directly to achieving significant gains in electrolyte stability at the lithium metal electrode interface and, consequently, enhancements in actual cell performance.”

Study co-author Dr Pooja Goddard, from Loughborough University, said, “The Li–O₂ battery remains an important and desirable target towards improving energy storage capacity for next-generation battery devices.

“Li–O₂ batteries have remarkably high theoretical specific energy (the amount of energy stored per unit weight), and therefore the realisation of a practical and truly rechargeable Li–O₂ device with even a fraction of the theoretical capacity could outperform state-of-the-art lithium-ion cells.

“Through the use of both calculations and experimental data, we were able to identify the key physical parameters that enabled the formulations to become stable against the lithium metal electrode interface.

“If the stability and performance of Li–O₂ batteries can be optimised, Li–O₂ devices could enhance, for example, driving range capacity significantly for electric vehicles.”

The designed electrolytes provide new benchmark formulations that will support ongoing investigations within the university research groups to understand and develop new, and practically viable, cathode architectures to reduce round-trip inefficiencies and further extend cycle lifetimes.

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