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Abstract :
[en] The emerging market of the Internet of Things, smart objects and others increase
the demand for micro energy sources. Rechargeable Li-ion batteries are a well-known technology
for energy storage. However, safety issues and high production costs constrain progress. Research
on solid electrolytes, such as LiPON, was performed to evade leakage. But LiPON suffers from low
ionic conductivity and a cost and time intensive production process. Another approach is the
substitution of volatile and flammable organic electrolyte solvents with ionic liquids (IL), which
display negligible vapor pressure and wide chemical, electrochemical, and thermal stability.
Electrolyte solution based on ILs can be confined into inorganic porous networks forming so-called
ionogels (IG), which are investigated as solid electrolyte materials. IGs combine low hazard and good
ionic conductivity [1].
Silica-based IGs compatible with Li/LiCoO2 systems were prepared in a one-pot sol-gel
process. The composition of the IG precursor solution and the influence of trifluoroacetic acid as
catalyst were studied to obtain a fast condensation. Homogeneous and transparent IGs were
obtained with a gelation time of less than 4 h. The physical properties of the host matrix were
characterized by N2 sorption, Hg porosimetry and SEM. The silica host matrices were 3D networks
predominantly built from 3-fold condensed silicon centres.
The influence of its structural changes on the electrochemical behaviour was studied by
varying the catalyst amount and by increasing the IL amount in the gel. The electrochemical
performances of the IG were measured with complex impedance spectroscopy and galvanostatic
cycling. Results show that IGs with IL amounts nIL/nSiO2~3 may be successfully used as solid
electrolyte in Li/LiCoO2 cells. Batteries were prepared, which cycle more than 100 cycles at a rate of
C/2 with no evidence of dendritic growth. Impedance characterization reveals the high internal
resistivity of these batteries due to the dense structure of the silica matrix.
