Title

Development of high performance air-cathodes for solid state lithium-air cells

Date of Award

2010

Degree Name

M.S. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Dr. Binod Kumar

Abstract

A solid state lithium-air battery is receiving considerable attention by the battery community recently. A challenging part of making a solid state lithium-air battery is to develop a solid state air-cathode. The present study relates to the development of the air-cathode. The air-cathode consists of a lithium ion conducting material, electron conducting material, metal substrate, binder and dispersant. For lithium ion conduction Lithium aluminum germanium phosphate (LAGP) glass-ceramic powder was used. For electron conduction two types of carbon were used. One type of carbon help in providing better electron conductivity and the other type of carbon helps in pore formation in the cathode. Nickel mesh/foam was used for structural support and current collection. Polytetrafluoroethylene (PTFE) was used to bind LAGP and carbon. Dispersant was used for preventing LAGP and carbon powders from agglomerating. The investigation includes evaluation of processing parameters including the effect of LAGP or dispersant concentration on the rate capacity. LAGP glass was prepared at 1350⁰C and crystallized at 850⁰C for 12 hours to transform it into a glass- ceramic. The cathodes prepared from the batch materials and processed were characterized to determine porosity, surface area, pore size and volume. To evaluate the electrochemical properties of these cathodes twelve lithium-air cells were fabricated and tested in the temperature range 45 - 115⁰C and were characterized using a Solartron 1260 impedance analyzer with 1287 electrochemical interface in oxygen atmosphere under 1 kPa pressure.It was determined that the use of dispersant helped the cathode obtain a porosity of 22% which is due to the proper dispersion of LAGP in cathode. A dispersant concentration of 5.92 wt% helped the cell discharge at a voltage of 2.5 V for 35 hours and achieved a capacity of 14.1 mAh at 75⁰C. LAGP concentration of 90 wt% helped in discharging the cell with a current of 0.50 mA for 13 hours at 75⁰C. The enhanced capacity of the cell is attributed to the catalyzing effect of LAGP for oxygen reduction. A capacity of 8.76 mAh was obtained at 67⁰C by having nickel foam side exposed to oxygen flow. The capacity was obtained because of the better oxygen transport inside the cathode.

Keywords

Cathodes Design and construction, Solid state batteries, Lithium cells

Rights Statement

Copyright 2010, author

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