The morphologies
that metal electrodeposits form during the earliest
stages of electrodeposition are known to play a critical role in the
recharge of electrochemical cells that use metals as anodes. Here
we report results from a combined theoretical and experimental study
of the early stage nucleation and growth of electrodeposited lithium
at liquid–solid interfaces. The spatial characteristics of
lithium electrodeposits are studied via scanning electron microscopy
(SEM) in tandem with image analysis. Comparisons of Li nucleation
and growth in multiple electrolytes provide a comprehensive picture
of the initial nucleation and growth dynamics. We report that ion
diffusion in the bulk electrolyte and through the solid electrolyte
interphase (SEI) formed spontaneously on the metal play equally important
roles in regulating Li nucleation and growth. We show further
that the underlying physics dictating bulk and surface diffusion are
similar across a range of electrolyte chemistries and measurement
conditions, and that fluorinated electrolytes produce a distinct flattening
of Li electrodeposits at low rates. These observations are rationalized
using X-ray photoelectron spectroscopy (XPS), electrochemical
impedance spectroscopy (EIS), and contact angle goniometry to probe
the interfacial chemistry and dynamics. Our results show that high
interfacial energy and high surface ion diffusivity are necessary
for uniform Li plating.
Solid‐state batteries enabled by solid‐state polymer electrolytes (SPEs) are under active consideration for their promise as cost‐effective platforms that simultaneously support high‐energy and safe electrochemical energy storage. The limited oxidative stability and poor interfacial charge transport in conventional polymer electrolytes are well known, but difficult challenges must be addressed if high‐voltage intercalating cathodes are to be used in such batteries. Here, ether‐based electrolytes are in situ polymerized by a ring‐opening reaction in the presence of aluminum fluoride (AlF3) to create SPEs inside LiNi0.6Co0.2 Mn0.2O2 (NCM) || Li batteries that are able to overcome both challenges. AlF3 plays a dual role as a Lewis acid catalyst and for the building of fluoridized cathode–electrolyte interphases, protecting both the electrolyte and aluminum current collector from degradation reactions. The solid‐state NCM || Li metal batteries exhibit enhanced specific capacity of 153 mAh g−1 under high areal capacity of 3.0 mAh cm−2. This work offers an important pathway toward solid‐state polymer electrolytes for high‐voltage solid‐state batteries.
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