Precipitated silica as filler for polymer electrolyte based on poly(acrylonitrile)/sulfolane
Beata Kurc
0
) Faculty of Chemical Technology, Pozna University of Technology
, 60 965 Pozna,
Poland
The aim of the present work was to perform a preliminary study of the physicochemical properties of hybrid organic-inorganic gel electrolytes for Li-ion batteries based on the PAN/TMS - poly(acrylonitrile)/sulfolane - polymeric matrix and surface-modified precipitated silicas. Modifications were done by means of the so-called dry method using silane U-511 3-methacryloxypropyltrimetoxysilane. Scanning electron microscopy (SEM), noninvasive back scattering method (NIBS), specific surface area (BET), the degree of modification of the silica fillersFourier-transform infrared spectroscopy (FT-IR), impedance analysis, and charging/ discharging were carried out. It is found that the silica fillers were homogeneously dispersed in the polymeric matrix, which enhanced conductivity and electrochemical stability of porous polymer electrolytes. Applicability of the prepared gel electrolytes for the Li-ion technology was estimated on the basis of specific conductivity measurements. It was shown that modification of the silica surface by the silane causes an increase in the gel-specific conductivity by about 2 orders of magnitude as compared to gel with unmodified silica.
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In recent years, much attention has been focused on the
development of new inorganicorganic composite materials
of prospective use in many areas [14]. Among the inorganic
substances, silicon dioxide has become greatly important as an
active filler of polymers [57]. Its importance follows from the
possibility of controlling its physical properties (by method of
synthesis) [8, 9] and chemical properties (by surface
modification) [10].
Gel-type electrolytes are regarded as a prospective
alternative for traditional liquid electrolytes as far as lithium-ion
(Liion) batteries are considered. Gel electrolytes are obtained by
placing some amount of liquid plasticizer and/or solvent in a
polymer matrix. This idea was first demonstrated in 1975 by
Feuillade and Perche [11] who studied the process of
plasticizing a polymer (host matrix) with an aprotic solution
containing an alkali metal salt. Since then, many different
polymers were examined as possible gel matrices, including
poly(vinylidene fluoride) (PVdF) [12], poly(acrylonitrile)
(PAN) [13, 14], poly(methyl methacrylate) (PMMA) [15],
and others.
The advantage of gel electrolytes over liquid electrolytes
lies in the fact that the risk of leakages in the battery systems
containing gels is reduced, since in principle, no free liquid is
present in such systems. In addition to that, their specific
conductivities are close to those exhibited by purely liquid
electrolytes.
As was demonstrated in the works of Gozdz and Tarascon
[16, 17], some gel electrolytes can have processing properties
that enable successful application in large-scale production
processes. One of the important findings of Gozdz and
Tarascon was that the addition of highly dispersed silica to
the PVdFHFP matrix significantly enhances the solvent
absorption ability, thus leading to a considerable increase in the
measured conductivities. The positive effect of various
ceramic particles (also Al2O3, TiO2, and others) on the
conductivities of dry polymer electrolytes is also well-documented in the
literature [1823]. The key factors responsible for the
performance of these ceramic additives are believed to be particle
size and surface chemistry. Caillon-Caravanier et al. [24]
found that the addition of unmodified silica provided better
mechanical stability and improved the solvent absorption
ability of membranes, thus enhancing the conductivities. In
more recent works, Lee et al. studied the possibility of
generating in situ fine silica particles dispersed in the PEO matrix
[21] as well as of functionalization of silica surface with glycol
chains [25]. Application of crosslinkable silicas modified with
certain methacrylate monomers was also reported [26].
Currently, the most widely used separators in lithium-ion
batteries are manufactured from polyolefins, predominantly
polyethylene (PE) or polypropylene (PP), due to their suitable
chemical stability, thickness, and mechanical strength [27].
However, several intrinsic factors such as low porosity, poor
thermal stability, and insufficient electrolyte wettability and
large difference of polarity between the highly polar liquid
electrolyte and the nonpolar polyolefin separator lead to high
cell resistance, low rate capability, and even internal short
circuits of LIBs [2830], which severely restricts the
electrochemical performance of the LIBs, especially affects the
safety performance of the LIBs. Therefore, the development of
new separators possessing high porosity, good thermal
stability, and high ionic conductivity is strongly demanded,
especially in the thermal stability which seriously influences the
practical application of LIBs.
In many studies, the fluorinated polymer poly(vinylidene
flu (...truncated)