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Lecture

WEB The growth of Li2O2 crystal in electrolyte solution of Li-Air batteries by ab initio simulations

Thursday (24.09.2020)
09:30 - 09:45 M: Modelling and Simulation 1
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Li-air batteries are widely investigated due to their ultra-high theoretical energy capacity (~3500 Wh kg-1), which roots in the formation of oxides (Li2O2 or Li2O) in the cathode. However, the insulating nature of the oxides leads to serious problems in the long-term stability of energy and rate capacity, which significantly hinders the practical application of the device. For Li-air batteries with aprotic solvents in the electrolyte, Li2O2 as the product of O2 reduction in the discharging process is generated via surface and/or solution-mediated pathway, mainly depending on the donor number of electrolytes. Formation of Li2O2 crystal with a toroidal shape yields high energy-density batteries and is associated with the solution-mediated disproportionation mechanim. However, the specific mechanism in electrolyte solution and the influence of solvents with different donor numbers remains unclear, in particular at atomistic resolution. In this work, we examine the growth of Li2O2 via the solution-mediated pathway in three common solvents with wide range of donor number by ab initio simulations. Thermodynamic analysis indicates the growth could take place on O-termianted Li2O2(001) and O-termianted Li2O2(100) with a layer by layer type and on both surfaces the growth process involves not only the chemical adsorption of LiO2 on Li2O2, but also the transfer of Li+ induced by electrostatic interaction. Ab initio molecular dynamics (AIMD) simulations with a LiO2 solvation model in three typical solvents (DMSO, DME and PC) show that the different interaction forces between the solvents and LiO2 induces different geometries of solvated LiO2. LiO2 with single Li-O bonds perfectly fits the lattice of (001), while the growth along (001) surface demands LiO2 both with single and double Li-O bonds. AIMD also pointed out the geometry of LiO2 generated on the catalyst surface will not influence the growth process due to the instant change of the geometries in solution by solvation. Our findings clarified the solution-mediated pathway for Li2O2 crystal growth and provided underpinning opinion for further modification of the solvent system and therefore a better battery.

 

Speaker:
Dr. Hongjiao Li
Karlsruhe Institute of Technology (KIT)
Additional Authors:
  • Prof. Dr. Wolfgang Wenzel
    KIT

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