Deep eutectic solvents
(DESs) have attracted extensive research
for their potential applications as leaching solvent to recycle valuable
metal elements from spent lithium ion batteries (LIBs). Despite various
advantages like being economical and green, the full potential of
conventional binary DES has not yet been harnessed because of the
kinetics during leaching. Herein, we consider the fundamental rate-determining-step
(RDS) in conventional binary DES and attempt to design ternary DES,
within which the chemical reaction kinetics and diffusion kinetics
can be regulated to maximize the overall leaching rate. As a proof
of concept, we show that the ternary choline chloride/succinic acid/ethylene
glycol (ChCl/SA/EG) type ternary DES can completely dissolve LCO powder
at 140 °C in 16 h. By systematically studying the leaching process
at various conditions, the energy barrier during leaching can be calculated
to be 11.77 kJ/mol. Furthermore, we demonstrate that the extraction
of the cobalt ions from the leaching solution can be directly achieved
by adding oxalic ions without neutralizing the solution. The precipitate
can be used to regenerate LCO with high purity. The recycled materials
show comparable electrochemical performance with commercial LCO. Our
design strategy of ternary DES with regulated RDS is expected to have
both scientific and technological significance in the field of hydrometallurgical
recycling of LIBs.
The further development of fast electrochemical devices
is hindered
by self-discharge. Current strategies for suppressing self-discharge
are mainly focused on the extrinsic and general mechanisms, including
Faradaic reactions, charge redistribution, and Ohmic leakage. However,
the self-discharge process is still severe for conventional supercapacitors.
Herein, we unravel the deterministic effect of a solid-state diffusion
energy barrier by constructing conjugately configured supercapacitors
based on pairs of prelithiated niobium oxides with similar intercalation
pseudocapacitive processes but different phases. This device works
with a single type of charge carrier, while materials with various
diffusion barriers can be implanted, thus serving as an ideal platform
to illustrate the influence of diffusion barrier. The results show
that the comprehensive effect of the solid-state diffusion barrier
and extrinsic effects drives the self-discharge process. It is worth
noting that the diffusion barrier presents an exponential form, which
governs the self-discharge of supercapacitors. This work provides
a general guidance for suppressing self-discharge for supercapacitors.
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