The original poly(ethylene
oxide)-based polymer electrolytes normally
show low ionic conductivity and inferior mechanical property, which
greatly restrict their practical application in all-solid-state lithium-ion
batteries (LIBs). In this work, a hyperbranched star polymer with
poly(ethylene glycol) methyl ether methacrylate flexible chain segments
is embedded into a three-dimensional (3D) interpenetrating cross-linking
network created by the rapid one-step UV-derived photopolymerization
of the cross-linker (ethoxylated trimethylolpropane triacrylate) in
the presence of lithium salt. The rigid 3D network framework provides
the polymer electrolyte with not only enhanced mechanical behavior,
including film-forming and dendrite-inhibiting capabilities, but also
nanoconfinement effects, which can speed up polymer chain segmental
dynamics and reduce the crystallinity of the polymer. Depending on
this unique rigid–flexible coupling network, the prepared solid
polymer electrolyte shows enhanced ionic conductivity (6.8 ×
10–5 S cm–1 at 50 °C), widened
electrochemical stability window (5.1 V vs Li/Li+), and
enough mechanical stability to suppress the growth of uneven Li dendrite
(the Li symmetrical cells can operate steadily at both current densities
of 0.05 and 0.1 mA cm–2 for 1000 h). Moreover, the
assembled LiFePO4//Li cell also exhibited good cycle performance
at 50 °C, making the hyperbranched star polymer electrolyte with
a nanoconfined cross-linking structure to have potential application
in high-safety and high-performance LIBs.
Lignin
is an eco-friendly, low-cost, and abundant natural biopolymer.
However, few studies have explored the potential application
of lignin as electrolyte matrix for lithium-ion batteries or obtained
excellent cell performance using lignin-based electrolyte. In this
paper, lignin and poly(N-vinylimidazole)-co-poly(poly(ethylene glycol) methyl ether methacrylate)
are mixed thoroughly in water, then a free-standing lignin-based film
is obtained by casting and drying. The resulting film shows obviously
higher mechanical strength (over 10 times) than that of the pure lignin
film due to the construction of internal physical cross-linking network.
Through activation of the prepared film by organic electrolyte, the
membrane exhibits superior electrochemical performances (such as outstanding
lithium-ion transfer number (0.63) and the ability to inhibit the
growth of lithium dendrites). As a result, the LiFePO4/lignin-based
electrolyte/Li cell presents excellent long cycle performance (∼150
mAh g–1 at 1 C more than 450 cycles) and rate capacity
(110 mAh g–1 at 10 C) at room temperature (RT),
which is better than that of the cells using a commercial separator.
Moreover, the LiCoO2/lignin-based electrolyte/Li cell also
shows superior cell performance at RT. Thus, the lignin-based electrolyte
with the outstanding comprehensive property has the potential to replace
separator and to be widely applied in high-performance and high-safety
LIBs.
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