anodes exceeds that of the best-performing multi-component systems with
and without conductivity-enhancing additives that are reported to date
(Table S3).36-45 We tuned mass-loading of TzG/Si@Cu
electrodes that lead to similar excellent performance (Supplementary
information Table S2, Section S2.6, Figure S17-S19). For example,
we were able to increase the Si
mass-loading of the electrode beyond 1 mg cm-2 by a
two rounds of polymerisation on top of a TzG/Si@Cu electrode in the
presence of small quantities of Cu(OAc)2 as an
additional source of Cu(II) species (Supplementary Information Section
S1.6, Table S2). The obtained electrodes show a stable cycling
performance and comparably high capacities as electrodes obtained in a
one-step growth process (Figure S19).
TzG is a thermally stable polymer with a decomposition onset above
400 °C under air.10 Hence, we tested the performance
of the TzG/Si@Cu half-cell after a heat treatment of 80 °C for 6 h,
above temperatures experienced by Li-ion batteries in some industrial
and military settings. The overall performance of the TzG/Si@Cu
half-cell after the thermal-stress test remains at
~3000 mA h g-1 in the second cycle
comparable to the performance of untreated electrodes. The difference in
overall capacity and in capacity retention can be attributed to partial
decomposition of LiPF6 during the extended heat
treatment (Figure S20). As a proof of concept, we assembled a full cell
using TzG/Si@Cu as the anode and the commercially available standard
NCM811 as the cathode (Figure S21 and S22). The NCM811 cathode was
selected over three commercial options (NCM532, NCM622, and NCA) as the
one with the highest specific capacity and most stable cycling
performance. We believe that full-cell assemblies with better coulombic
efficiencies can be achieved using cathodes that (i) match the high
capacity of our anode better, and (ii) have similar diffusion kinetics.
Conclusion
We present here a one-pot synthetic protocol that yields
high-performance silicon anodes within one hour of reaction time. These
anodes consist of silicon nanoparticles that are fully encapsulated by a
semi-conducting, porous triazine-based graphdiyne (TzG) polymer that
grows directly on the Cu current collector. Cu foil plays three roles in
this paradigm-changing method of anode fabrication: it acts (i) as a
source of Cu species for a Glaser‐type oxidative coupling
polymerization, (ii) as templating substrate for the polymer film, and
(iii) as the current collector of the electrode. The porous ,
semi-conducting TzG polymer acts (i) as a strong, flexible binder that
envelops Si NPs with a matrix of covalent bonds that can sustain the
dramatic volume changes of silicon in repeated de-/lithiation cycles and
prevents detrimental abrasion and reformation of the solid electrolyte
interface, (ii) as a facilitator of charge transport along its
π-conjugated polymer backbone, and (iii) as a medium for mass transport
of lithium ions and electrolyte through its microporous channels. The
resulting anodes achieve stable electrochemical cycling performance and
an extraordinarily high capacity close to the theoretical limit of
electrochemical storage using silicon. The reported process uses raw
materials and methods common in industrial electrode manufacture and can
be transferred and scaled up with ease. Half-cell electrode assemblies
in the off-state retain key performance parameters even after thermal
stress, and full-cell cycling tests using commercial cathodes
demonstrate the viability of this technology in commercial applications.
Acknowledgements
We thank Dr. Martin Dračínský for
solid-state NMR measurements, Dr. Petr Formánek for TEM imaging and
mapping, Prof. Dr. Jürgen P. Rabe for access to Raman spectroscopy. J.H.
thanks Dr. Mathias Trunk for providing monomer materials, Weimiao Wang
for Raman spectra discussion and analysis. M.J.B. thanks the European
Research Council (ERC) for funding under the Starting Grant Scheme
(BEGMAT-678462) and the Proof of Concept Grant Scheme (LiAnMat-957534).
Keywords: graphdiyne • glaser-coupling • Li-ion battery •
silicon anode • one-pot
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