Don’t hold your breath for lithium-air cells
- 著者:Ella Cai
- 公開：:2017-08-18
Rechargeable lithium air batteries could save a lot of weight, if only they could be made to work.
Now MIT has proved another hopeful additive is flawed, although the understanding developed could help in the search for others.
Like zinc-air non-rechargeables, the idea is to replace one energy-containing electrode material with oxygen, which is breathed in from the atmosphere.
“But that theoretical promise has been limited in practice because of three issues: the need for high voltages for charging, a low efficiency with regard to getting back the amount of energy put in, and low cycle lifetimes, which result from instability in the battery’s oxygen electrode,” said the Massachusetts Institute of technology.
Organic additives to the electrolyte have been proposed to sort some of these issues, except they are not themselves stable, according to MIT. A lithium iodide additive, which is inorganic and more likely to remain stable, has also be proposed to address the problems, but published findings have been contradictory, with some showing LiI does improve the cycling life, and some that LiI leads to irreversible reactions and therefore short cycle life.
The university set out to at least find out what is happening with LiI. “We explored in detail how lithium iodide affects the process, with and without water,” said scientist Michal Tulodziecki.
The team looked at the role of LiI on lithium-air battery discharge, with one set of experiments conducted with the components outside of the battery, allowing the reaction to be examined bit by bit, and the set done a battery to help explain the overall process.
Techniques including ultra-violet and visible-light spectroscopy revealed that compounds such as LiOH (lithium hydroxide) are forming, instead of the desired Li2O2 (lithium peroxide).
LiI can enhance water’s reactivity and make it lose protons easily, which promotes the formation of LiOH, and this interferes with the charging process.
So either an alternative to LiI has to be found, or some way to suppress the formation of LiOH is needed.
The findings “help get to the bottom of this existing controversy on the role of LiI on discharge. We believe this clarifies and brings together all these different points of view,” said Professor Yang Shao-Horn.
The work was supported by Toyota Motor Europe and the Skoltech Center for Electrochemical Energy Storage, and used facilities supported by the National Science Foundation. It appears in the journal Energy and Environmental Science as ‘The role of iodide in the formation of lithium hydroxide in lithium–oxygen batteries‘.
Image: The reaction that occurs during the charging of a lithium oxygen battery using lithium iodide as an additive. Credit: Jose-Luis Olivares MIT
Now MIT has proved another hopeful additive is flawed, although the understanding developed could help in the search for others.
Like zinc-air non-rechargeables, the idea is to replace one energy-containing electrode material with oxygen, which is breathed in from the atmosphere.
“But that theoretical promise has been limited in practice because of three issues: the need for high voltages for charging, a low efficiency with regard to getting back the amount of energy put in, and low cycle lifetimes, which result from instability in the battery’s oxygen electrode,” said the Massachusetts Institute of technology.
Organic additives to the electrolyte have been proposed to sort some of these issues, except they are not themselves stable, according to MIT. A lithium iodide additive, which is inorganic and more likely to remain stable, has also be proposed to address the problems, but published findings have been contradictory, with some showing LiI does improve the cycling life, and some that LiI leads to irreversible reactions and therefore short cycle life.
The university set out to at least find out what is happening with LiI. “We explored in detail how lithium iodide affects the process, with and without water,” said scientist Michal Tulodziecki.
The team looked at the role of LiI on lithium-air battery discharge, with one set of experiments conducted with the components outside of the battery, allowing the reaction to be examined bit by bit, and the set done a battery to help explain the overall process.
Techniques including ultra-violet and visible-light spectroscopy revealed that compounds such as LiOH (lithium hydroxide) are forming, instead of the desired Li2O2 (lithium peroxide).
LiI can enhance water’s reactivity and make it lose protons easily, which promotes the formation of LiOH, and this interferes with the charging process.
So either an alternative to LiI has to be found, or some way to suppress the formation of LiOH is needed.
The findings “help get to the bottom of this existing controversy on the role of LiI on discharge. We believe this clarifies and brings together all these different points of view,” said Professor Yang Shao-Horn.
The work was supported by Toyota Motor Europe and the Skoltech Center for Electrochemical Energy Storage, and used facilities supported by the National Science Foundation. It appears in the journal Energy and Environmental Science as ‘The role of iodide in the formation of lithium hydroxide in lithium–oxygen batteries‘.
Image: The reaction that occurs during the charging of a lithium oxygen battery using lithium iodide as an additive. Credit: Jose-Luis Olivares MIT
