1,002 research outputs found
How Voltage Drops are Manifested by Lithium Ion Configurations at Interfaces and in Thin Films on Battery Electrodes
Battery electrode surfaces are generally coated with electronically
insulating solid films of thickness 1-50 nm. Both electrons and Li+ can move at
the electrode-surface film interface in response to the voltage, which adds
complexity to the "electric double layer" (EDL). We apply Density Functional
Theory (DFT) to investigate how the applied voltage is manifested as changes in
the EDL at atomic lengthscales, including charge separation and interfacial
dipole moments. Illustrating examples include Li(3)PO(4), Li(2)CO(3), and
Li(x)Mn(2)O(4) thin-films on Au(111) surfaces under ultrahigh vacuum
conditions. Adsorbed organic solvent molecules can strongly reduce voltages
predicted in vacuum. We propose that manipulating surface dipoles, seldom
discussed in battery studies, may be a viable strategy to improve electrode
passivation. We also distinguish the computed potential governing electrons,
which is the actual or instantaneous voltage, and the "lithium cohesive energy"
based voltage governing Li content widely reported in DFT calculations, which
is a slower-responding self-consistency criterion at interfaces. This
distinction is critical for a comprehensive description of electrochemical
activities on electrode surfaces, including Li+ insertion dynamics, parasitic
electrolyte decomposition, and electrodeposition at overpotentials.Comment: 35 pages. 10 figure
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