Enhancing capacity and rechargeability of lithium-air batteries by precise control of reaction zone dimensions and mediators

• Applicant: Professor Dr. Axel Groß
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces ; Solid State and Surface Chemistry, Material Synthesis
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405821363

• Final Report Year: 2022

Final Report Abstract

The original goal of this joint German-Russian project was to improve the reversibility of Li-air batteries by preventing the deposition of the electrically insulating main discharge product Li2 O2 on the cathode. This should be achieved by controling the dimensions of the reaction zone in which the discharge product Li2 O2 is formed through introducing electrochemically inactive cations to the electrolyte and thus displacing the discharge intermediate LiO2 from the electrode surface. Molecular dynamics simulations had provided some promising results in this respect. However, the experiments performed within this project showed that the Li+ concentration close to the electrode is still high enough to provide the second electron transfer resulting in surface passivation instead of possible LiO2 disproportionation in electrolyte bulk. Therefore we decided to systematically study the details of the formation of the main discharge products of nonaqueous Li-O2 batteries. First we derived the equilibrium shape of the particles formed from the two discharge products Li2 O and Li2 O2. By determining the most prominent surface terminations, possible routes to avoid the passivation of the electrode surfaces might be identified. Furthermore, by performing ab initio molecular dynamics simulations in the Blue Moon ensemble, we derived the free energies along the reaction paths in the LiO2 dissociation and disproportionation reactions, showing that these reactions should occur spontaneously in typical electrolytes used in Li-air batteries. These studies represent first steps towards a more complete first-principles based understanding of the crucial processes occurring in Li-air batteries which is needed to overcome obstacles in their reversible operation.

Publications

• First-Principles Study of the Surfaces and Equilibrium Shape of Discharge Products in Li–Air Batteries. ACS Applied Materials & Interfaces, 13(21), 24984-24994.
  Didar, Behnaz Rahmani; Yashina, Lada & Groß, Axel
  
• Impact of Cathodic Electric Double Layer Composition on the Performance of Aprotic Li-O2 Batteries. Journal of The Electrochemical Society, 168(3), 030520.
  Isaev, Valerii V.; Sergeev, Artem V.; Zakharchenko, Tatiana K.; Itkis, Daniil M.; Groß, Axel & Yashina, Lada V.
  
• Solvation structure and dynamics of Li and LiO2 and their transformation in non-aqueous organic electrolyte solvents from first-principles simulations. Chinese Journal of Catalysis, 43(11), 2850-2857.
  Didar, Behnaz Rahmani & Groß, Axel