posted on 2020-07-22, 21:09authored byYuta Kimura, Mahunnop Fakkao, Takashi Nakamura, Toyoki Okumura, Nozomu Ishiguro, Oki Sekizawa, Kiyofumi Nitta, Tomoya Uruga, Mizuki Tada, Yoshiharu Uchimoto, Koji Amezawa
Designing
composite electrodes with optimal microstructure, composition,
and choice of active material (AM) as well as solid electrolyte (SE)
is critically important for the development of high-performance solid-state
batteries (SSBs). To optimize AM loading, which includes loading amount,
composition, and dispersion state, and to maximize AM utilization
in composite SSB electrodes, we need to precisely understand how the
AM loading affects electrochemical reactions taking place in the electrodes.
Here, using computed tomography combined with X-ray absorption near
edge structure spectroscopy (CT-XANES), we performed operando three-dimensional (3D) observations of electrochemical reactions
in composite SSB electrodes with different AM loading amounts to understand
the influence of the AM loading on the electrochemical reactions.
In the composite electrode with higher AM loading amount, the lower
reacted regions were mainly found at the inner parts of the aggregated
AM regions. It was suggested that such a reaction distribution resulted
from the slow intergranular ion transport between AM particles. In
the composite electrode with lower AM loading amount, the electrochemical
reaction progressed more homogeneously compared to the one with higher
loading. This is probably because the lower AM loading mitigated the
AM aggregation and decreased the number of high-resistance AM–AM
interfaces that Li ions must pass through. Such a reaction distribution
formation due to the slow ion transport between the AM particles can
be a serious restriction in composite SSB electrodes. This is in marked
contrast to conventional liquid-based lithium ion battery (LIB) electrodes,
in which a majority of AM particles can directly exchange Li ions
with the surrounding liquid electrolyte. Therefore, the optimal design
for composite SSB electrodes can significantly differ from that for
liquid-based LIBs. Our analysis technique can provide valuable information
to rationally design optimal composite electrodes, and hence we expect
that this technique contributes to the further development of high-performance
SSBs.