Unusual improvement of pseudocapacitance of nanocomposite electrodes: Three-dimensional amorphous carbon frameworks triggered by TiO2 nanocrystals
writer：王海
keywords：TiO2, amorphous carbon, pseudocapacitance, lithium-ion batteries, anode materials
source：期刊
specific source：ACS Applied Materials & Interfaces
Issue time：2019年
Both nanocrystals and carbon materials have attracted considerable
attention in the field of lithium-ion batteries (LIBs), due to their fast
kinetics for lithium storage or long-life cycles. However, the easy aggregation
of nanocrystals and high-temperature doping process of carbon materials
seriously hindered their application in LIBs. Here we report the development of
unprecedented TiO2-x@C nanocomposite electrodes through a unique
"melting-low temperature pyrolysis" strategy. It is found that in
this composite structure, the continuous and interconnected three-dimensional
amorphous carbon framework (3DCF) was closely connected by TiO2
nanocrystals by Ti-O-C covalent bonding, forming robust 3D network
architectures. Interestingly, we found that TiO2 nanocrystals can
greatly improve the pseudocapacitance of TiO2-x@C nanocomposite
electrodes with increasing cycles, which significantly exceeded previously
reported TiO2-based anodes and carbon materials. Furthermore, for
the first time, the unusual improvement of pseudocapacitance of TiO2-x@C
electrodes were carefully investigated by means of dQ/dV curves and electrochemical
kinetic analysis to reveal the extra contribution of lithium storage. 3DCF, a
“lithium ion reservoir”, possesses an unexpected capacity enhancement behavior
that is triggered by TiO2 nanocystals, and exhibited bicontinuous
pathways for both rapid ions and electrons transport. In this case, TiO2 nanocrystals
stabilizing 3DCF acted as a conductive agent during charge and discharge. Our findings
confirm that 3DCF triggered by TiO2 nanocrystals boosted electrochemical
performance of TiO2-x@C nanocomposite electrodes, especially the
pseudocapacitance enhancement. The unique characteristics of ingenious
combination of TiO2 nanocrystals and amorphous carbon materials make
them obtain superior electrochemical properties in all known TiO2-x
and carbon-based anodes (289 mAh g-1 at 5 A g-1 after
4000 cycles). Above all, our findings reveal previously ignored fundamental
aspects of pseudocapacitance improvement of nanocomposite electrodes, and offer
new hope for structural design and carbon coating process of high-performance
anode materials.