Ac impedance: A tool for interrogation of lithium and lithium ion battery cathodes
Multani, Kuldeep Singh
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My thesis project involves study of EIS, electrochemical impedance spectroscopy, which is a unique method of interpreting the electrochemistry of lithium ion batteries in the form of an electrical circuit in order to improve its electrochemical properties. EIS is done by applying a sinusoidal voltage to the electrochemical cell in a fixed frequency range and its response is collected in the form of sinusoidal current which is latter analyzed using Z-View software. We can select various frequency ranges from 0.001 Hz to 10 5 Hz, depending on the active material and testing conditions. I used this novel technique in my projects; such as the storage time study, in which I studied the maximum storage time of the non-discharged, partially discharged and complete discharged Li/Ag 2 VO 2 PO 4 , silver vanadium oxide cells by correlating the AC impedance resistance with its DC internal resistance. The next study involves the optimal synthesis of different polymer binders for the coatings which are then used as cathode in lithium ion batteries. Basically, I used 3 different categories of binders; PVDF, Poly-acrylic acid with polyethylene oxide (filler) neutralized by LiOH.H 2 O and by NaOH. I used LiCoO 2 , a rechargeable cathode material to test these binders by doing cycling, discharge, pulse test and using ac impedance technique.