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U Waterloo team shows four-electron conversion for Li-O2 batteries for high energy density; inorganic molten salt electrolyte, high temperature

Chemists from the University of Waterloo have successfully resolved two of the most challenging issues surrounding lithium-oxygen batteries, and in the process created a working battery with near 100% coulombic efficiency.

The new work, published in Science, shows that four-electron conversion for lithium-oxygen electrochemistry is highly reversible. The Waterloo team is the first to achieve four-electron conversion, which doubles the electron storage of lithium-oxygen, also known as lithium-air, batteries.

Xia

Thermodynamics and configuration of the Li-O2 cell. (A) Gibbs reaction energy for formation of Li2O and Li2O2 as a function of temperature. The thermodynamic data were calculated according to the database of HSC chemistry version 5. (B) Configuration of the inorganic electrolyte Li-O2 cell and schematic illustration of Li2O formation during discharge. Xia et al.

There are limitations based on thermodynamics. Nevertheless, our work has addressed fundamental issues that people have been trying to resolve for a long time.

—Linda Nazar, Canada Research Chair of Solid State Energy Materials and senior author

The high theoretical-energy density of lithium-oxygen (Li-O2) batteries and their relatively light weight have made them a key focus for R&D for next-generation battery systems, especially for EVs. However, long-standing issues with the battery’s chemistry and stability have kept them in the realm of academia.

Two of the more serious issues involve the intermediate of the cell chemistry (superoxide, LiO2) and the peroxide product (Li2O2) reacting with the porous carbon cathode, degrading the cell from within. In addition, the superoxide consumes the organic electrolyte in the process, which greatly limits the cycle life.

Nazar and her colleagues switched the organic electrolyte to a more stable inorganic molten salt and the porous carbon cathode to a bifunctional metal oxide catalyst.

We demonstrate that by increasing the operating temperature and exploiting stable inorganic electrolytes and ORR catalysts, the reversible formation of Li2O leads to a highly rechargeable Li-O2 cell with high capacity, low overpotential with transfer of 4 e/O2, and excellent cycling performance.

—Xia et al.

By operating the battery at 150 ˚C (302 ˚F), they found that the more stable product Li2O is formed instead of Li2O2. This results in a highly reversible Li-oxygen battery with coulombic efficiency approaching 100 per cent.

By storing O2 as lithium oxide (Li2O) instead of lithium peroxide (Li2O2), the battery not only maintained excellent charging characteristics, it achieved the maximum four-electron transfer in the system, thereby increasing the theoretical energy storage by 50%.

By swapping out the electrolyte and the electrode host and raising the temperature, we show the system performs remarkably well.

—Linda Nazar

Resources

  • C. Xia, C. Y. Kwok, L. F. Nazar (2018) “A high-energy-density lithium-oxygen battery based on a reversible four-electron conversion to lithium oxide” Science Vol. 361, Issue 6404, pp. 777-781 doi: 10.1126/science.aas9343

Comments

As Aha

perfect chemistry for Leafs cookbox :D

Engineer-Poet

It sounds like similar operating conditions as the Zebra battery, but with much improved performance.  Let's hope this one goes places.

Davemart

This is a much lower and more practical temperature than the zebra battery:

' The ZEBRA battery must be heated to 270–350°C (518–662°F), a temperature that is lower than the original sodium-sulfur battery. Even with special insulation that minimizes heat loss, heating consumes 14 percent of the battery’s energy per day. Since the energy to keep the battery hot is taken from the battery, the resulting parasitic load amounts to 18 percent. This can be compared with the high self-discharge of a battery. A cool down takes 3 to 4 days; depending on SoC, reheating is about 2 days.'
https://batteryuniversity.com/index.php/learn/article/bu_210a_why_does_sodium_sulfur_need_to_be_heated

Its a lot higher than the 60-80 C that the Bollore Blue car ran at, and that did not work out and has been discontinued:
https://www.blue-solutions.com/wp-content/uploads/2014/09/BLUESOLUTIONS_RA_GB_MEL-01072014.pdf

gryf

Also the ZEBRA battery has been used in vehicle applications. For example, the Irizar 12e 376 kWh Electric Bus or an experimental 1993 Mercedes-Benz C-Class (W 202).

Paroway

If the manufacturing cost is reasonable this could well begin life as a stationary storage battery. With that kind of density they should be saving on the expensive components. At 150C you also have the cogen capabilities of heating water.

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