Oxidation of Ethylene Carbonate on Li Metal Oxide Surfaces

Thomas Mandal Østergaard, Livia Giordano, Ivano Eligio Castelli, Filippo Maglia, Byron Antonopoulos, Yang Shao-Horn, Jan Rossmeisl
Accepted for publication in Journal of Physical Chemistry C.

Abstract:

Understanding the reactivity of the cathode surface is of key importance to the
development of batteries. Here Density Functional Theory is applied to investigate
the oxidative decomposition of the electrolyte component, ethylene carbonate (EC),
on layered LixMO2 oxide surfaces. We compare adsorption energy trends of atoms
and small molecules, on both surface oxygen and metal sites, as function of the Li
content of the surface. The oxygen sites are identified as the reactive site for the
electrolyte oxidation reaction (EOR). We report reaction energies and NEB-calculated
kinetic barriers for the initial oxidative decomposition of EC, and correlate both with
the reaction energy of hydrogen adsorption on oxygen. The hydrogen adsorption energy
scales with the distance between the Fermi level and the O-2p band center. We expect
this model of the EOR to be valid for other organic electrolytes and other Li metal
oxide surfaces, due to its simplicity, and the model leads to simple design principles for
protective coatings.

Download database files with structures and energetics, and scripts for plotting figures

database keywords:
Database: DB.db:
keyword=surf  :  [ 'LiVO2', 'Li05VO2', 'VO2', 'LiCrO2', 'Li05CrO2', 'CrO2', 'LiMnO2', 'Li05MnO2', 'MnO2', 'LiFeO2', 'Li05FeO2', 'FeO2', 'LiCoO2', 'Li05CoO2', 'CoO2', 'LiNiO2', 'Li05NiO2', 'NiO2' ]

keyword=ads  : ['M_H', 'O', 'OH', 'CO', 'H', 'vac', 'slab', 'EC_rmH', 'EC_chemi', '4H_2vac', 'NEBai', 'NEBa1', 'NEBa2', 'NEBa3', 'NEBa4', 'NEBaf', 'NEBbi', 'NEBb1', 'NEBb2', 'NEBb3', 'NEBb4', 'NEBb5', 'NEBb6', 'NEBb7', 'NEBbf', 'NEBci', 'NEBc1', 'NEBc2', 'NEBc3', 'NEBc4', 'NEBc5', 'NEBc6', 'NEBc7', 'NEBc8', 'NEBc9', 'NEBc10', 'NEBcf' ]

keyword=TS  : ['TSb']

explaination: M_H is hydrogen on the metal site, H is hydrogen on the oxygen site, vac is an oxygen vacancy, 4H_2vac is oxidation state 1 in figure 8 of the paper, EC_chemi is the chemisorbed state of EC (not used), EC_rmH is the oxidized state of EC, NEBax is image x of the NEB-calculated reaction pathway where EC chemisorbs from a physisorbed state. NEBb is the subsequent proton transfer and vacancy formation pathway, and NEBc contains the direct proton transfer pathway (found in SI of the paper).

TS='TSb' is used as an extra marker for the transition state between the chemisorbed and the oxidized state (TS2 in figure 2 of the paper),

Not all keywords are available for all surfaces. And overview of the database can be generated with this script.

Database: DB_mol.db:
keyword=mol  :  ['EC', 'H2', 'H2O', 'CO', 'CO2']