Despite
the important role of carboxymethyl cellulose (CMC) and
styrene–butadiene rubber (SBR) binders in graphite electrodes
for Li-ion batteries, the direct analysis of these binders remains
challenging, particularly at very low concentrations as in practical
graphite anodes. In this paper, we report the systematic investigation
of the physiochemical behavior of the CMC and SBR binders and direct
observations of their distributions in practical graphite electrodes.
The key to this unprecedented capability is combining the advantages
of several analytic techniques, including laser-ablation laser-induced
break-down spectroscopy, time of flight secondary ion mass spectrometry,
and a surface and interfacial cutting analysis system. By correlating
the vertical distribution with the adsorption behaviors of the CMC,
our study reveals that the CMC migration toward the surface during
the drying process depends on the degree of cross-linked binder-graphite
network generation, which is determined by the surface property of
graphite and CMC materials. The suggested analytical techniques enable
the independent tracing of CMC and SBR, disclosing the different vertical
distribution of SBR from that of the CMC binder in our practical graphite
anodes. This achievement provides additional opportunity to analyze
the correlation between the binder distribution and mechanical properties
of the electrodes.
To
realize the potential high capacity of lithium–oxygen
(Li–O2) batteries, a double oxygen supply system
for cells with high-loading cathodes is devised in this study. High-loading
thick electrodes can achieve exceptionally high capacities, but this
promise has been plagued by partial utilization of thick electrodes
in Li–O2 cells due to the kinetic limitation imposed
by oxygen transport. The proposed double oxygen supply system provides
oxygen gas to the cathode not only from the cathode opening but also
from the separator side to ensure sufficient oxygen supply to the
whole high-loading electrode. Subsequently, the entire region of the
high-loading cathode is rendered active, resulting in a uniform vertical
distribution of discharge products. The maximum utilization of the
high-loading electrodes is, thus, achieved, along with a remarkably
increased capacity, low overpotential, and cycle life. By this strategy,
CNT cathodes can be cycled with a capacity of 5 mAh cm–2, without using any additional catalyst.
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