Chemical and Biological Engineering ETDs

Kyle Fenton

Publication Date

2-8-2011

Abstract

Printable lithium iron phosphate (LiFePO4) cathodes and porous aerogel / polymer separators have been designed, constructed, and tested. The cathodes consist of LiFePO4, PVDF binder, and conductive carbon which was developed for robocast deposition (printing) onto carbon coated aluminum substrates to form 60 \uf06dm thick cathodes. Electrochemical and physical evaluation of these printed cathodes was performed to determine capacity, rate capability, and lifetime performance of the printed cathodes. Cells were constructed using a standard 2032 coin cell to ensure uniform electrode size and pressure on the layers of the battery. Cathodes printed exhibited up to 115 mAh/g capacity with a commercial separator and have 89% retention of capacity after 60 continuous charge / discharge cycles. The physical characteristics for the printed cathodes were evaluated using SEM and EDS techniques to determine the morphology of the cathodes as printed. Several polymers were evaluated to identify applicability for a printed separator. In order to allow for the resulting printed separator to remain porous, an aerogel material was added to the printing slurry before deposition. The materials were evaluated for rheological properties and printing results to identify an optimal material for a printable separator. The polypropylene/polyethylene material identified as a suitable printed separator was printed directly onto printed cathodes and electrochemical and physical evaluations were conducted on the resulting battery material to determine ability to cycle and rate capability. The printed cathode and separator exhibited up to 60 mAh/g capacity. An optimal ratio between the polymer binder and the aerogel porous component was established based upon testing in a 2032 coin cell using liquid electrolytes. The ratio of binder to aerogel which exhibited the highest electrochemical performance in a full cell was predicted to have the lowest performance. This unexpected relationship was explored based upon impedance measurements of the cells. The performance of these battery components printed using the robocasting technique was compared to current alternative technologies. The resulting comparison indicates that printed battery constituents using the robocasting technique is a viable method for developing printed lithium battery systems which exhibit similar performance to alternative techniques. Additionally, the robocasting technique for battery development allows for printing of battery materials in nearly any geometry in both planar and three dimensional systems depending on the application needs.

Keywords

lithium battery, lithium iron phosphate, direct write, printable, separator, robocasting; Lithium cells--Design and construction.

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Apblett, Chris

Second Committee Member

Petsev, Dimiter

Third Committee Member

Ward, Tim

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