posted on 2021-07-27, 11:38authored bySvetlana Menkin, Christopher A. O’Keefe, Anna B. Gunnarsdóttir, Sunita Dey, Federico M. Pesci, Zonghao Shen, Ainara Aguadero, Clare P. Grey
“Anode-free”
batteries present a significant advantage
due to their substantially higher energy density and ease of assembly
in a dry air atmosphere. However, issues involving lithium dendrite
growth and low cycling Coulombic efficiencies during operation remain
to be solved. Solid electrolyte interphase (SEI) formation on Cu and
its effect on Li plating are studied here to understand the interplay
between the Cu current collector surface chemistry and plated Li morphology.
A native interphase layer (N-SEI) on the Cu current collector was
observed with solid-state nuclear magnetic resonance spectroscopy
(ssNMR) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry
(CV) and time-of-flight secondary ion mass spectrometry (ToF-SIMS)
studies showed that the nature of the N-SEI is affected by the copper
interface composition. An X-ray photoelectron spectroscopy (XPS) study
identified a relationship between the applied voltage and SEI composition.
In addition to the typical SEI components, the SEI contains copper
oxides (CuxO) and their reduction reaction
products. Parasitic electrochemical reactions were observed via in situ NMR measurements of Li plating efficiency. Scanning
electron microscopy (SEM) studies revealed a correlation between the
morphology of the plated Li and the SEI homogeneity, current density,
and rest time in the electrolyte before plating. Via ToF-SIMS, we
found that the preferential plating of Li on Cu is governed by the
distribution of ionically conducting rather than electronic conducting
compounds. The results together suggest strategies for mitigating
dendrite formation by current collector pretreatment and controlled
SEI formation during the first battery charge.