Commercial
lithium-ion batteries are vulnerable to fire accidents,
mainly due to volatile and flammable liquid electrolytes. Although
solid polymer electrolytes (SPEs) are considered promising alternatives
with antiflammability and processability for roll-to-roll mass production,
several requirements have not yet been fulfilled for a viable lithium
polymer battery. Such requirements include ionic conductivity, electrochemical
stability, and interfacial resistance. In this work, the ionic conductivity
of the SPEs is optimized by controlling the molecular weight and structural
morphology of the plasticizers as well as introducing propylene oxide
(PO) groups. Electrochemical stability is also enhanced using ethylene
oxide (EO)/PO copolymer electrolytes, making the SPEs compatible with
high-Ni LiNi
x
Co
y
Mn1–x–y
O2 cathodes. The in situ cross-linking method, in
which a liquid precursor first wets the electrode and is then solidified
by a subsequent thermal treatment, enables the SPEs to soak into the
60 μm thick electrode with a high loading density of more than
8 mg cm–2. Thus, interfacial resistance between
the SPE and the electrode is minimized. By using the in situ cross-linked
EO/PO copolymer electrolytes, we successfully demonstrate a 4 V class
lithium polymer battery, which performs stable cycling with a marginal
capacity fading even over 100 cycles.
Recently,
the development of silicon-based anodes for lithium-ion batteries
has attracted tremendous attention for overcoming the disadvantages
of commercial graphite-based anodes. In this work, we suggest a chemical
methodology of synthesizing silicon–carbon composite anodes,
with capacity values of 763 and 182 mAh/g at current densities of
0.1 and 5 A/g, respectively. An electrostatic assembly technique is
designed to be triggered by a cationic polyelectrolyte, poly(ethylenimine),
for negatively charged silicon nanoparticles and graphene oxides.
Amine-functionalized carbon nanotubes are synthesized in a nondestructive
fashion and incorporated additionally to provide intraconnected conductive
pathways between neighboring composite materials. It is revealed that
the electrochemical performance of intraconnected composite materials
is determined by the chemical/physical factors of constituent compartments.
The applicability toward all-solid-state batteries is also suggested
with usage of a solid polymer electrolyte synthesized from a mixture
of bisphenol A ethoxylate diacrylate, polyethylene glycol dimethyl
ether, tert-butyl peroxypivalate, and bis(trifluoromethane)sulfonimide
lithium salt.
The volatility of liquid electrolytes
is a major obstacle in the
fabrication of efficient lithium-ion batteries that are safe. Solid-state
electrolytes such as solid polymer electrolytes have been studied
as a potential substitute for liquid electrolytes. However, their
practical application is impeded owing to their low ionic conductivity
and high interfacial resistance between the electrolyte and electrodes.
Herein, we synthesize a novel ionic liquid crosslinker and use thermal
crosslinking to prepare a gel polymer electrolyte (GPE), which shows
a higher thermal stability than that of liquid electrolytes and a
better ionic conductivity than that of solid electrolytes. The crosslinker,
IL2, is designed to have a pyrrolidinium-bis(trifluoromethyl sulfonyl)amide
structure and an acrylate terminal group with an ethylene oxide spacer
connected between them. IL2-GPE, which is prepared by in situ thermal
crosslinking, shows an ionic conductivity up to 5.37 mS cm–1 and high thermal and electrochemical stabilities. A cell with IL2-GPE
sandwiched between a LiFePO4 cathode and lithium anode
exhibits a capacity above 160 mA h g–1 and a high
rate capability. By combining a crosslinker having four acrylate terminals
with the IL2 crosslinker, we obtain HIL2-GPE, whose ionic conductivity
is 20% higher than that of IL2-GPE. The HIL2-GPE cell exhibits capacities
of 165 and 146 mA h g–1 at 0.1 and 1.0 C, respectively,
thereby demonstrating better performance than that of the cell with
IL2-GPE. We also prepared a cell using high-voltage cathode LiNi0.6Co0.2Mn0.2O2 (NCM622).
The result suggested that the cell based on the GPEs maintained superior
long-term stability even with high-voltage cathode materials over
100 cycles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.