2.1. Preparation of electroactive LTO-separator
A slurry of 90 wt.% Li4Ti5O12 (LTO), 7 wt.% polymeric binder (polyvinylidenfluorid
hexafluoropropylene copolymer (PVDF-HFP),
KYNAR FLEX PPA 2801), 3 wt.% carbon black (Super P-Li, Timcal) in
N-ethyl-2-pyrrolidon (NEP) was prepared by stirring over night with
a magnetic stirrer. This slurry was coated on a PET non-woven by
doctor blading which was then dried in a vacuum furnace at 120 C
over night. A typical loading of 8.5 mg cm2 LTO was achieved. Subsequently,
this ‘LTO-separator’ was lithiated by immersing it over
night in 10ml of n-butyl-lithium(15wt.% in n-hexane). This stepwas
done in an argon filled glovebox. During lithiation the LTO-separator
changed its color fromgray to black. Pristine LTO is white, but due to
the carbon black content of the coated layer, the appearance is gray,
which easily allows determining the quality of the LTO layer on the
white non-woven prior to lithiation. The carbon black furthermore
ensures a good electronic conductivity within the LTO layer which
was found to be essential for a proper functioning. After lithiation, the
sheet was thoroughly washed in n-hexane (>99% purity, BASF) in
order to remove the n-butyl-lithium, which would otherwise react
with the carbonate components of the electrolyte. The n-hexanewas
removed by washing in ethyl methyl carbonate. Additional lithium
loading was gravimetrically determined to be around 0.14 mg cm2.
As the theoretical capacity of LTO is 175 mAh g1, resulting in a
maximum lithium storage capability of w0.34 mg cm2 for a separatorwith
LTOloading of 8.5mgcm2, it can be assumed, that the LTO
was only partially lithiated, despite the over night soaking in n-butyllithiumand
the final composition of the lithiated LTOin the separator
was Li4þxTi5O12.
2.1. Preparation of electroactive LTO-separatorA slurry of 90 wt.% Li4Ti5O12 (LTO), 7 wt.% polymeric binder (polyvinylidenfluoridhexafluoropropylene copolymer (PVDF-HFP),KYNAR FLEX PPA 2801), 3 wt.% carbon black (Super P-Li, Timcal) inN-ethyl-2-pyrrolidon (NEP) was prepared by stirring over night witha magnetic stirrer. This slurry was coated on a PET non-woven bydoctor blading which was then dried in a vacuum furnace at 120 Cover night. A typical loading of 8.5 mg cm2 LTO was achieved. Subsequently,this ‘LTO-separator’ was lithiated by immersing it overnight in 10ml of n-butyl-lithium(15wt.% in n-hexane). This stepwasdone in an argon filled glovebox. During lithiation the LTO-separatorchanged its color fromgray to black. Pristine LTO is white, but due tothe carbon black content of the coated layer, the appearance is gray,which easily allows determining the quality of the LTO layer on thewhite non-woven prior to lithiation. The carbon black furthermoreensures a good electronic conductivity within the LTO layer whichwas found to be essential for a proper functioning. After lithiation, thesheet was thoroughly washed in n-hexane (>99% purity, BASF) inorder to remove the n-butyl-lithium, which would otherwise reactwith the carbonate components of the electrolyte. The n-hexanewasremoved by washing in ethyl methyl carbonate. Additional lithiumloading was gravimetrically determined to be around 0.14 mg cm2.As the theoretical capacity of LTO is 175 mAh g1, resulting in amaximum lithium storage capability of w0.34 mg cm2 for a separatorwithLTOloading of 8.5mgcm2, it can be assumed, that the LTOwas only partially lithiated, despite the over night soaking in n-butyllithiumandthe final composition of the lithiated LTOin the separatorwas Li4þxTi5O12.
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