Figure 2. Characterization of TzG/Si@Cu electrodes usinga , X-ray photoelectron spectroscopy (XPS) data from the Si 2p
region, b , transmission electron microscopy (TEM), andc , scanning electron microscopy (SEM). Data is presented for
TzG/Si@Cu electrodes in the pristine state (i), after the first
lithiation (ii), after the first delithiation (iii) and after the
100th delithiation (iv). Cycling was performed using
constant current mode at C/8 within a voltage range of 0.01-1.2 V vs.
Li+/Li.
Ex-situ TEM and SEM imaging of TzG/Si@Cu electrodes at different cycling
stages (Figure 2b and c) reveal that prior to cycling, the TzG polymer
acts as a binder that joins Si NPs into a porous TzG/Si composite (i).
After the first lithiation, individual particles of increased size can
be discerned that correspond to lithiated and volumetrically expanded
domains of LixSi, all embedded in a fabric of polymer
and SEI (ii). After the first delithiation, the size of the spherical Si
domains decreases (iii), and after the 100th-cycle
delithiation, all that can be said is that the TzG/Si composite shows no
discernible large cracks or deformations (iv) (Figure S11 and S12).
A comprehensive discussion of these findings is presented in
Supplementary Information section S2.2. For now, we conclude that: (i)
the alloying reaction between lithium and Si NPs takes place unhindered,
hence, the TzG polymer matrix allows lithium to diffuse, (ii) the
conductivity enhancing additive in TzG/Si/CB@Cu has no positive effect
on the performance of TzG-based electrodes, hence, the initial, modest
conductivity of undoped TzG is no impediment for its use in electrodes;
and (iii) the TzG polymer does not participate in the detrimental
depletion of lithium or electrolyte on its own, and SEI formation occurs
exclusively in the presence of Si NPs. It is particularly surprising
that TzG-based electrodes perform as well as they do, given their