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DateDate: 25-08-2018, 07:29

Chemists from the University of Waterloo have successfully solved two main problems in the way of creating a lithium-oxygen battery. In the process they developed a battery with Coulomb efficiency of almost 100%. The study confirms the high reversibility of four-electron conversion in the electrochemistry of lithium-oxygen devices, sciencedaily.com reports. Conclusions of the project are presented in Science. The team was the first to achieve four-electron conversion, doubling the capacity of lithium-oxygen (air) batteries.
"There are thermodynamic limitations," explained Professor Linda Nazar, senior author of the work. "Nevertheless, our project is devoted to fundamental problems that people have been trying to solve for a long time."
The main difficulty was the reaction of intermediate and peroxide products (LiO2 and Li2O2) with a porous carbon cathode. The first compound, superoxide, also absorbs the organic electrolyte in the process, which greatly limits the life of the battery.
Nazar and his colleagues decided to replace the latter compound with a more stable inorganic molten salt. Instead of a carbon anode, a bifunctional metal oxide catalyst was used. Running the battery at 150 ° C, scientists observed the formation of a more stable Li2O instead of Li2O2. As a result, a highly reversible lithium-air battery with a Coulomb efficiency of almost 100% was obtained.
Replacement of peroxide with oxide provided not only the preservation of high charge characteristics, but also a four-electron transfer, increasing the theoretical energy intensity by 50%.
"A new electrode, electrolyte and a rise in temperature led to a good work of the system," concluded Professor Nazar.
Put more energy into batteries is the key to creating electric vehicles with a longer run, smartphones with "eternal" charge and cheap electronics around and everywhere. Lithium-oxygen batteries are one of the most promising ways of development in this direction.
They can increase the energy density by several orders of magnitude in comparison with traditional lithium-ion batteries - at least in theory.
In a paper published yesterday in the journal Science, scientists from the University of Waterloo figured out how to solve the biggest obstacles to the formation of these batteries in the role of commercial reality.
What was the catch? Most importantly: when lithium-oxygen batteries were discharged, oxygen was converted to superoxide and then into lithium peroxide, reactive components that corroded the battery over time.
This, in turn, limited its ability to recharge - and possible useful application.
When will we have better batteries?
What changed? To solve this problem, scientists have moved from a carbon cathode to a nickel oxide cathode with the support of a stainless steel mesh.
Also, the electrolyte used was a fused salt - the electrolyte allows the positively charged ions to move between the electrodes - and raised the operating temperature of the battery to 150 degrees Celsius.
This allowed us to increase the number of charge cycles by almost three times compared to conventional lithium-oxygen variants.
Scientists also managed to increase the energy content per unit mass by more than 50%.